The characterization of atmospheric pressure ionization/tandem mass spectrometry for direct atmospheric analysis

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Title:
The characterization of atmospheric pressure ionization/tandem mass spectrometry for direct atmospheric analysis
Physical Description:
viii, 117 leaves : ill. ; 28 cm.
Language:
English
Creator:
Matuszak, Kenneth Paul, 1961-
Publication Date:

Subjects

Subjects / Keywords:
Atmospheric ionization   ( lcsh )
Atmospheric pressure   ( lcsh )
Mass spectrometry   ( lcsh )
Chemistry thesis Ph. D
Dissertations, Academic -- Chemistry -- UF
Genre:
bibliography   ( marcgt )
non-fiction   ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1988.
Bibliography:
Includes bibliographical references.
Statement of Responsibility:
by Kenneth Paul Matuszak.
General Note:
Typescript.
General Note:
Vita.

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Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 001115795
oclc - 19956069
notis - AFL2518
System ID:
AA00002145:00001

Full Text















CHARACTERIZATION OF
MASS SPECTROMETRY


ATMOSPHERIC
FOR DIRECT


PRESSURE IONIZATION/TANDEM
ATMOSPHERIC ANALYSIS


KENNETH


PAUL MATUSZAK


A DISSERTATION PRESENTED TO
OF THE UNIVERSITY
IN PARTIAL FULFILLMENT OF THE
DEGREE OF DOCTOR OF


THE GRADUATE
OF FLORIDA
REQUIREMENTS
PHILOSOPHY


UNIVERSITY


OF FLORIDA


1988


SCHOOL




































my parents


with


love.














ACKNOWLEDGEMENTS


wish


express


sincere


appreciation


Richard


Yost


for his


guidance


direction


during


the completion


of this


work.


would


also


like


acknowledge


thank


the members


graduate


committee


John


Eyler,


Hoflund,


John


Dorsey,


Cliff


Johnston.


acknowledge


at Tyndall,


the U


, which


.Air


provided


Force


Engineering


the entire


support


Services


for this


Center,


work.


Many


thanks


to the departmental


machine,


electronics


glass


shops


, including


Russ


Pierce


of the electronics


shop


bailed


me out


several


times


with


insights


knowledge,


ability


explain


electronics


refined


level;


design


Steve


oversaw


Miles


electronics


construction


corona


shop


discharge


current-regulated


power


supply;


Chester


Eastman,


Vern


Cook,


Dailey


Burch


of the machine


shop


constructed


almost


the entire


source


took


time


of their


schedules


for last


minute


changes


during


crunch-


time;


and Dr


. Sam


Colgate


for his


advice


on vacuum


system


design.


thank


fellow


researchers,


especially


Mark


Hail


helped


extensively


early


this


project,


Jodie


Johns on


for his


mass


spectrometry


advice,


Mark


Bolgar who


assisted on


the project,


fellow


group


members,


especially


Mike


,my


roommates


Bryan


Hearn


Mike








especially


Paul


Anne


McCaslin,


Regina


Cheong,


little


bro'


Jeff


Keaffaber.


Sincere


thanks


family


, especially


Dad,


have


been


so supportive


friends


back


home


in Chicago


the members


Augustine


Catholic


Church


Inter-Varsity


Christian


Fellowship


for uplifting me


in their


prayers.


most


special


thanks


person


held


me up


here


at the


end,


wouldn't


me quit,


took


care


me when


needed


with


even


when


was


a jerk,


made


my days


bright


even


when


were


dark,


never


ceased


to shower


me with


love


, my very


soon-


to-be


wife


, Laura


Elizabeth


Boudreaux


love


that


name).


Last

because


but

it was


not

only


least,


thank


grace


that


Lord

had t


Jesus


Christ


:he ability


Savior,


strength


finish.















TABLE


OF CONTENTS


PAGE


ACKNOWLEDGEMENTS... . . . . . . . . .


ABSTRACT. . . . .aa a . . . a


CHAPTER


INTRODUCTION. .. .. .. ... .. . ...


Analytica
Overview
Overview


Scenario


of API/MS.
of Thesis


Organi


zation.


S. .. .. .. . 13


DESIGN


Overall
Initial


OF THE API


System Des


Source


SOURCE. .. ... ... ... ... .. .


. a .. a. .. . a. a a a...a a
* a a a a a a a a a a e O 1 6 4 Q 4 4


Design.


Source
Source


Configuration
Configuration


Finnigan
Finnigan


4500
TSQ


EXPERIMENTAL RESULTS


SOURCE


Results


with API


Finnigan


450


Source
0 Mass


Configuration f
Spectrometer...


Adaptation


of the API


Source


to the


Finnigan
Experimental
and Mass


70 Mass


Physical


Spectrometer.


Parameters


of API


Spectrometer


Clustering/Declustering.


Source


. .. 58
.. .. 74


Experimental


Methods


Direct Atmospheric


Monitoring


80


Sampling Methodology...


S... .. 81


ANALYTICAL PERFORMANCE. .... . ... .... ... ... .. ...


Characterization


of the API/MS/MS


Instrument


....4 ... ... 82


Analytical

CONCLUSIONS


Potential..


FUTURE WORK.. ... . . . .....


C, 4. 1,. F D I* 1


DEVELOPMENT..............


C lr iw ftia.







LITERATURE CITED . . . . . . a . . . . 114

BIOGRAPHICAL SKETCH. . . ............ .. . . . . 117














Abstract
University


Dissertation


Florida


Presented


in Partial


the Degree


Characterization


to the Graduate


Fulfillment


Doctor


of Atmospheric


Philo


Pressure


School


of the


f the Requirements
sophy


lonization/Tandem


Mass


Spectrometry


Direct


Atmospheric


Analysis


Kenneth


Paul


Matuszak


April,


1988


Chairman:


Major


Richard A.


Department:


Yost


Chemistry


Atmospheric


pressure


ionization


(API)


been


shown


to be


very


useful


when


combined


with


tandem mass


spectrometry


in performing


direct


atmospheric


monitoring


trace


compounds.


design


development


a new


source


that


been


developed


compatible


with


commercial,


turbomolecularly-pumped


triple


stage


quadruple


(TSQ)


tandem


mass


instrument


spectrometer


been


used


(MS/MS)


study


presented.


direct


This


atmospheric


API/MS/MS


sampling


mass


spectrometry,


production


ions


the atmosphere,


effects


supersonic


expansion


clustering


these


ions


with


neutral


species


, (4)


effectiveness


declustering


these


r, n 1 n n: rr an 1


nrti ni 4 r,,r117 1 x


i rvn G 'h


a-h 4 1 4 ttrr


maarrric


Tn -


Tr n


i^n







groundwork


the development


an instrument


capable


of performing


trace


analysis


while


performing


direct


atmospheric


monitoring.


This


source


utilizes


a corona


discharge


primary


ionization


atmospheric


molecules


orifice


system


selectively


leak


ions


into


mass


analysis


region.


It has


been


constructed


that


interchangeable


with


a standard


electron


ionization


(EI)/chemical


ionization


(CI)


source


on a Finnigan-MAT


triple


quadruple


tandem


mass


spectrometer.


developing


this


source


, a program


to model


the ion optics


(SIMION)


been


used


to aid


in the design


of the post-orifice


lens


configuration.


design


this


source


such


that


memory


effects


have


been


essentially


eliminated


the clustering


of ions


with


molecules


in the


post-orifice


region


been


significantly


reduced.


Samples


that


have


been


studied


include


a variety


of laboratory


solvents.


These


solvents


have


been


inj ected


into


streams


pure


nitrogen


carrier


have


been


analyzed


under


direct


atmospheric


conditions


bringing


caps


of the solvent


bottles


near


the sampling


region


of the API


source.


Recommendations


are


made


overcoming


limitations


present


source


design


lens


system.


These


include


consideration


of supersonic


expansion


theory


to redesign


post-


orifice


lens


system


additional


modifications


discharge


needle


system.












CHAPTER


INTRODUCTION


purpose


develop,


this


a new


work


atmospheric


twofold:


pressure


first


ionization


design,


(API)


construct,


source


turbomolecularly-pumped


triple


stage


quadruple


(TSQ)


tandem


mass


spectrometer


/MS)


, and


second,


characterize


apply


this


new


source


study


direct


atmospheric


sampling


mass


spectrometry,


production


ions


atmosphere,


effects


supersonic


expansion


clustering


these


ions


with


neutral


species,


collisional


effectiveness


means


declustering


ability


these


qualitatively


ions


identify


atmospheric


gases.


These


studies


will


serve


to lay


the groundwork


development


an instrument


capable


of performing


trace


analysis


while


could


performing


be used


direct


an airport


atmospheric


"sniffer"


monitoring.


drugs


Such


instrument


explosives


or as


an on-line


vapor


detector


in the microchip,


incineration,


or chemical


production


industries.


maj or


use


of such


an instrument,


however,


anticipated


an environmental


monitor


chemical


waste


spills


chemical


dump


sites


or other


forms


of environmental


contamination.


Scenario


Analytical









commercial


tandem


mas s


spectrometer,


one


such


use


would


preliminary


pollution


detection


device,


that


to use


this


instrument


to perform


direct


atmospheric


analysis


, sampling


at various


locations


determining


possible


contamination


each


area


analysis.


Thus


, the instrument


in that


configuration


would


be able


perform


preliminary


identification


the pollutants


present,


as well


quantitation


to determine


extent


contamination.


Once


site


of contamination


was


found,


source


could


interchanged


with

could


the standard


be used


EI/CI


to analyze


source

soil


and

and


the

water


instrument

samples i


in this


configuration


n the surrounding


area


with


ionization


techniques


which


are


already


established


standardized


these


forms


sample


matter.


this


way,


extent


of contamination


could


be mapped


full


environmental


scheme


of air


, water,


soil.


Overview


of API/MS


Background


History


of API/MS


perform


the analysis


of atmospheric


gases


mass


spectrometry


there


are


two basic


approaches.


Because


a mass


spectrometer


operates


under


high


vacuum,


case


a quadruple


instrument


torr,


pressure


atmospheric


sample


must


vastly


reduced.


first


approach


(Figure


1.1)


to bleed


the atmospheric


sample


through


orifice


membrane


use


high-vacuum


pumps












cuum


Arm


ospner


Inte fa


B
B8

B


B
B

B
3 B8
A
8B


B A888
BA B B
B B


Ion


Pump


Ana


yz,


Figure


An atmospheric


mass


sampling


spectrometric


press


methodology i:
ures and then


n which g
ionized.


is reduced


:o normal


I
I









analyte


is pumped


away


with


excess


gas.


trace


analysis


this


obviously


undesirable.


second


method


(Figure


to somehow


ionize


the analyte


atmospheric


pressure


focus


the ions


through


a small


orifice


into


mass


analysis


region


means


electrostatic


fields,


while


pumping


away


excess


gas.


unique


ionization


technique


mass


spectrometry.


Ionization


mass


occurs outside

spectrometer at


of the

L the


mass

ions


analysis


are


(high


permitted


vacuum)


region


enter


high


vacuum


region,


usually


sub-millimeter


orifice


thin


diaphragm.


Molecules


an atmospheric


pressure


can


be ionized


passing


high


energy


electrons


through


allowing,


molecules


collide


with


these


electrons.


This


ionization


process


can


produce


both


positive


negative


ions.


Positive


ions


are formed


when


an electron


collides


with


a gaseous


molecule


causes


a second


electron


to be ejected,


as in Equation


(1.1)


Negative


ions


are


generated


when


a low


energy


(near


thermal)


electron


absorbed


a molecule


gas,


Equation


This


is called


electron


capture


ionization.









cuum


Int


tmospher


e rfa


8
B

B


B 3+


SB-"


n


B+
B- B


B
B
B

A
B
B


So
R^ c


B+
3 B+
81


Ion


Ana


yz


Pump


Figure


I
i


B


3 A









These


ions


can


further


react


with


background


molecular


species


form


background


analysis


, positive


reagent


ions


ions.


are formed


when


case


direct


molecules


atmospheric


in the


air


react


with


the high


energy


electrons


(Equations


1.4).


These


reactions


ions


can


through


further


collisions


react


with


char


other


ge exchange


background


proton


molecules


transfer


(Equations


to form


reagent


ions.


+ +


H2O+


HO+O


H30+


Sample


molecules


can


react


with


these


reagent


ions


proton


transfer


or charge


exchange


to form


molecular


(M+)


or pseudo-molecular


(M+H+)


ions


(Equations


H30+


M+H+


(1.8)


clusters


can


also


formed


when


ions


associate


with


neutral


species


before


the orifice


or in the supersonic


expansion


in the


post-


orifice


region.


molecular


weight


molecules


readily


form


clusters


HoO+


HoO+








(1.9)


M+H+

H30+


M+H2O+

M+H30+


H(H20)


(1.11)


.12)


preliminary


studies


with


a commercially


developed


never


marketed


source


an attempt


to perform


direct


atmospheric


monitoring,


as many


as 20


water


molecules


have


been


observed


cluster


with


a hydronium


(Equation


1.13)


form


a distribution


water


cluster


ions


(Figure


H3O+


nH20


H(H20)n+l+


where


- 1-20


(1.13)


At atmospheric


pressure,


molecules


will


undergo


multiple


collisions


those


with


highest


proton


affinity


(for


positive


ions)


highest


electron


affinity


(for


negative


ions)


will


quickly


become


ionized


means


of charge


or proton


transfer


with


ions


from


bulk


gas.


Because


this


a collisional


energy


transfer


, API


a low


energy


process


therefore


little


fragmentation


molecular


analyte


will


occur.


Also


, due to the multiple


collisions


, chemical


thermal


equilibria


will


established


thus


there


should


nearly


100%


ionization


efficiency


analyte


molecules


that


very


possess


high


these


sensitivity.


characteristics.


High


These


selectivity


factors


is also


should


obtained


lead


certain


classes


of compounds


because


of this


non-democratic


process.


C~~~ ~ ~ ~ nea 4n. aI C n- ---


C? ---- r:-


,P t,,,


n,,


1



















0N
N


IN


asoupunqy


Saf3AT 0T1









Knews tubb


Sudgen


[2-5].


They


used


a 50


jpm sampling


orifice


thin


platinum


foil


attached


a water-cooled


block,


sampling


ions


produced


in an atmospheric


flame


, to study


the combustion


chemistry


flames.


Their


system


utilized


three


stages


of differential


pump ing


reduce


pressure


from


atmospheric


down


to less


than


torr


in the


analyzer


region


of their magnetic


deflection mass


spectrometer.


Kebarle


chemistry


co-workers


ionization


used a-particle


processes


radiation


to study


"spectroscopically


pure"


gases


near


atmospheric


pressure.


Their


system


utilized


a 75


orifice


sample


ions


from


these


pure


gases


into


differentially


pumped


magnetic


deflection mass


spectrometer


at pressures


less


than


10-6


torr,


a similar


instrument


that


used


Knewstubb


Sudgen.


They


found


that


spectra


from


gases


were


dominated


ions


from


trace


impurities


in the


gases,


especially


from water.


Kebarle


used


these


findings


production


study


water


kinetics


cluster


ions


ionization


of the form


(H20)nH+


process

. former


and the

d in the


post-orifice


adiabatic


expansion


from


atmospheric


pressure


source


to the high


vacuum


of the


mass


spectrometer.


At about


same


time,


Shahin


developed


a system


mass


spectrometric


study


corona


discharges


atmospheric


pressures.


products


were


sampled


using


pm aperture


into


differentially


pumped


region.


This


analyzer


region


quadruple


mass


analyzer)


was


maintained


at about


x 10-


torr.


major


positive


ions


that


observed


were


(H20)nH+


(H20)nNO+


clusters


10-6


[6-8]


I


*








Analytical


API/MS


excellent


API/MS


articles


the currently


[11-12]


available


review


API/MS


detail


technology.


history


Because


soft"


ionization


technique,


maj or


positive


ions


formed


detected


with


mass


spectrometry


are


molecular


pseudo-


molecular


((M+H)+)


, and


cluster


, (Mx+H)


[M(H


ions.


In the API


source


chemical


thermal


equilibria


are establish


owing


large


number


collisions


occurring


atmospheric


pressure.


This


leads


a nearly


100%


ionization


efficiency


compounds


with


either


high


proton


electron


affinities


absolute


ionization


efficiency


a normal


source


is approximately


ion for


every


molecules


a CI


source


be 10


or 100


times


greater


than


this


[11.


Therefore


an API


source


great


potential


a very


sensitive


ionization


source.


Many


researchers


have


taken


advantage


of this


used


sources


conj unction


(LC)


with


supercritical


articles


-15],


chromatography


fluid


Horning,


(GC)


chromatography


al. ,


liquid


(SFC).


reported


chromatography


a series


development


API/MS


system


for analysis


of GC effluents.


In 1973


they


demonstrated


detection


nicotine,


cocaine,


methadone,


of caffeine


in 1


of chloroform


GC/API/MS


using


negative


ions.


Also


analyzed


were


barbiturates


extracted


from


urine


, in


p/g/mL


concentration


range.


Mitchum


[16-17]


used


Extranuclear


API/MS


instrument


detect


((M)+),


((Mx)+


O)x+H


[11].









Tsuchiya


Taira


[18],


Carroll


19 ,


Scott


et al.


Arpino


have


developed


LC/API/MS


systems


applied


them


a variety


of sample


types.


Because


the design


sources


described


above,


cleanliness


of the


source


these


instrument


instruments


were


was


extremely


characteristically


important.


very


Source


small


regions


cm3)


this


lead


contamination


memory


effects.


These


sources


also


suffered

problems


from

would


orifice


have


clogging


been


even


and

more


clustering


evident


problem

these


sources


these

had


two

been


used as


direct


atmospheric


monitors.


While


performing


direct


atmospheric


analyses,


energy


method


values


likely


from


produce


components


ions


same


same


molecular


mass to-charge


weight.


(m/z


order


distinguish


fragments


such


these


compounds


compounds.


therefore


However,


necessary


fragmentation


look


caused


without


first


isolating


the ion


of interest,


it would


be impossible


tell


which


ions


were


fragments


merely


ions


formed


from


other


compounds.


Thus,


perform


direct


atmospheric


analysis


with


an API


source,


a separation


step


is needed


before


mass


analysis.


API/Tandem Mass


Soectrometry


Much


work


been


performed


showing


that


a mass


spectrometer


used


mass


separation


technique


followed


second


mass


spectrometer


sample


analysis


22].


Presently,


only


three


examples


have


been


reported


sources


being


installed


tandem


mass


20] ,


can









Corporation


reported


installing


its commercially


available


source


on a tandem mass


spectrometer


as of this


writing


that


system


is not


commercially


available.


Sciex


Inc.


developed


a API/MS/MS


system


with


liquid


helium


cryogenic


pumping.


This


system


seen


most


analytical


system


date,


although


conventional


mass


spectrometric


ionization


techniques


cannot


be used


with


this


mass


spectrometer.


This


instrument


been


shown


Bruins


et al.


to be applicable


to LC


[26-


means


an "ion


spray"


interface


for the analysis


of sulfonated


azo dyes


to SFC


the analysis


of anabolic


steroids


20-30


concentration


level.


Snyder


have


used


Sciex


API/MS/MS


instrument


with


pyrolysis


probe


analyze


various


pharmaceuticals


in commercial


polymer


matrices


mobile


Sciex


TAGA


6000


been


applied


dioxin


analysis


detection


of explosives


in airports


31].


While


the Sciex


instrument


seen


a wide


spectrum


use


most


analyses


performed


with


can


more


easil


performed


with


conventional,


true


standardized


advantage


methods


source.


utilizing


However,


EI/CI


ionization.


because


liquid


helium


cryopumping


vacuum


system,


this


instrument


cannot


operated


near


appreciable


levels


of hydrogen


or helium


gas,


vacuum


system has


essentially


no pumping


speed


for those


gases.


other


tandem


mass


spectrometer


system


direct


atmospheric


analysis


that


needs


addressed


that


built


Glish


usa









tandem


quadrupole/time-of-flight


mass


spectrometer


for analysis.


This


source


been


used


to analyze


the head


space


vapor


of drinking water


with


trichloroethylene,


head


space


vapor


over


trinitrotoluene


(saturated


head


space


vapor


concentration


trinitrotoluene


is approximately


Overview


ppb).


of Thesis


Organization


This


thesis


is divided


into


chapters.


This


introductory


chapter


provides


background


material


on atmospheric


pressure


ionization


(API)


marriage


with


mass


spectrometry


(MS)


help


reader


understand


the research


described


in succeeding


chapters.


Chapter


constructed


describes


this


design


work


interfacing


source


which


been


different


mass


spectrometers


Problems


and characteristics


of other


early


sources


are described


to.emphasize


some


the features


of this


source.


third


chapter


describes


experimental


results


obtained


during


development


API/MS/MS


instrument


use


these


results


to guide


the development


of the API


source


to its final


form.


Included


this


chapter


are


descriptions


computerized


optic


modeling


which


was


used


to help


source


development


as an aid


gaining


an understanding


into


some


of the results


that


were


obtained.


description


analytical


performance


API/MS/MS


instrument


as a direct


atmospheric


monitor


can


be found


in Chapter









direct


atmospheric


analyses


proposes


future


work


that


should


help


attain


that


goal.











CHAPTER


DESIGN


OF THE API


SOURCE


In designing


a new


source


type


a mass


spectrometer,


design


mass


spectrometer


component


parts


must


taken


into


consideration.


source


this


work


was


developed


and modified


to work


with


two different mass


spectrometers.


Overall


System


Design


Even


though


the API


source


this


work was


eventually modified


be compatible


with


a Finnigan-MAT TSQ


70 triple-stage


quadrupole


tandem


mass


spectrometer,


inception


this


work


that


instrument


itself,


still


design


stages.


Initial


source


design


work


therefore


performed


Finnigan-MAT


4500


single


quadruple


mass


spectrometer


with


goal


of obtaining


a functional


source


that


could


later


be adapted


the specifications


mass


spectrometer


at hand.


Early


attempts


developing


sources


performing


direct


atmospheric


analyses


suffered


from


many


problems


, not


least


which


were


severe


memory


effects


from


previously


analyzed


samples,


clogging


of the orifice,


and clustering


of the sample


ions


with


neutral


was


was









required


clean


these


sources,


including


electropolishing


stainless


acetone


steel


surfaces,


methanol,


boiling


baking


deionized


temperatures


water,

greater


washing


with


than


Indeed,


an API


source


developed


(but


never


marketed)


Finnigan


that


generated


water


cluster


spectrum


in Chapter


(Figure


demonstrated many


of these


problems.


Figure


a schematic


drawing


this


source


which


similar


design


many


early


sources.


characteristics


of this


source


include


a small


source


region


(approximately


in volume),


a discharge


needle


high


energy


electron


supply,


adjustable


needle-to-orifice


distance,


sample


inlet


outlet


made


out


1/16"


stainless


steel


tubing,


single


orifice


interface


between


atmospheric


vacuum


regions.


During


operation


source


was


heated


ca.


in order


to reduce


memory


effects.


can


surmised


from


viewing


Figure


this


source


little


use


a direct


atmospheric


monitor


because


severe


clustering


problems.


To be fair


this


source


was


developed


as a


GC-detector


not


an atmospheric


monitor


even


a GC-detector


it suffered


from memory


effects


(because


of the small


source


region).


goals


of the development


aspect


of this


work


were


to develop


source


that


would


able


perform


real-time


atmospheric


monitoring,


amount


minimize


of clustering,


memory


achieve


interference


a high


effects,


sensitivity


minimize


compounds


interest.


Both


Finnigan-MAT


4500


quadrupole


triple






17









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regions.


Because


these


instruments


are


pumped


differentially,


a much


lower


vacuum


pumping


speed


required


maintain


anal


yzer


regions


at a sufficiently


pressure


that


performance


of the


analyzer


not


degraded)


than


a mass


spectrometer


which


is pumped


normal


means.


These


pumping


speeds


are


significantly


lower


than


those


used


previously


developed


API/MS/MS


instruments.


Sciex


reported


extremely


high


pumping


speeds


high


as 60.000


its cryo


much


genically


larger


pumped


orifice


instrument.


diameter


These


(>100


pumping


than


speeds


previously


allow


developed


instruments


(<20


Sciex


also


claims


that


the large


pumping


speeds


allow


very


quick,


large


drop


pressure


after


orifice


to avoid


the gas dynamics


problem


of shock


waves


at the end


the supersonic


expansion


of the


in this


region


However


differential


orifice


pump ing


diameters


of the Finnigan


order


instruments


of 70


also


this


allows


for larger


design.


since


each


two


Finnigan


instruments


easily


interchangeable


sources


lens


assemblies,


potential


developing


interchangeable


source


for these


instruments


was


good.


Initial


Source


Design


Initial


that


was


source


compatible


design


with


efforts


began


Finnigan-MAT


developing


4500


single


an API


quadrupole


source


mass


spectrometer


while


waiting


for the new TSQ


70 tandem mass


spectrometer.


[34].









stainless


steel


conflat


flange.


The Finnigan


EI/CI


source


assembly


mounted


onto


a similar


flange,


with


associated


electrical


feedthroughs


also


mounted


in this


flange.


In order


to reduce


interference


sample


memory


effects,


was


necessary


ionization region


To minimize


orifice


start


with


(Figure


the number


(a))


of lenses


quadruple


much


than


needed


entrance,


larger


used


internal


volume


the Finnigan API


for focusing


was


the ions


desirable


source.


from

have


orifice


close


possible


the pre-quadrupole


focusing


lenses.


Because


the distance


between


the face


of the flange


on the front


of the


instrument


entrance


to the quadrupoles


was


greater


than


source


held


canister


in place


was


designed


an o-ring.


inserted


limited


through


the outside


this


diameter


flange


of the


flange


less


than


, which


defined


inside


diameter


approximately


2.6"


significant


increase


over


diameter


source


region


of the old Finnigan API


source.


next


step


designing


source


direct


atmospheric


monitoring was


to develop


a system


to efficiently


draw


sample


into


source


past


discharge


region,


then


out


source


again.


This


was


accomplished


drawing


sample


through


concentric


glass


tubes


(Figure


.2(b))


, past


the discharge


region,


out


a side


port


attached


source


canister,


means


a common


laboratory


blower


instead


that


was


of blowing


modified


out,


draw


inner


sample


of the


(=100


two concentric


glass


mL/min)


tubes


was


, the



























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-4
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'-
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have


been


of high

a 63Ni


energy


foil


electrons


emitter


two most


a corona


common methods


discharge.


radioactive


continually


foil


advantages


emitting


steady


of using


flux


no external


electrons.


power


However,


electrons


it emits


have


a wide


energy


distribution


(the


most


probable


energy


being


ca.


keV),


this


energy


distribution


significant


tail


high


energies


[11].


a result,


spatial


distribution


reactant


ions


not


well


defined


the path


length


of the electrons


ions


vary


over


a wide


range


[11].


alternative


source


of high


energy


electrons


in API


a corona


discharge


from


the tip


a metal


needle


(often


a common


sewing


needle)


a planar


discharge


surface

provides


(usually


more


the plat

well


containing


defined


the diaphragm).


This


electrons


as well


as a much


higher


electron


flux.


other


advantage


the ability


to select


the needle to orifice


distance


which


used


to alter


the relative


intensity


distribution


of ions


produced


source.


However,


should


pointed


out


that


in order


obtain


true


corona


dischar


, a current-regulated,


high


voltage


to 10 kV)


current


limited


power


supply


is required.


Later


this


chapter,


the design


of such


a power


supply


is discussed


(there


presently


such


supplies


commercially


available)


however,


preliminary


work


was


performed


using


Bertan


205A-05R


voltage-


regulated


power


supply


which


provided


to 5000


35].


Because


this


a voltage-regulated


supply


, the


discharge


was


unstable


, and


this


a source


in API


spatial


distribution


was


are








lifetimes


(because


of sputtering


of the needle


tip)


an ion


signal


which


was


extremely


noisy.


provide


a supply


electrons


this


source


discharge


needle


was


mounted


in a teflon


ring which


threaded


into


outer


glass


tube


(Figure


2.2(c


attaching


the needle


to the tube


in this


way,


rough


control


needle


position


needle-to-orifice


distance


could


be accomplished


rotating


the glass


tube


or by


sliding


it in


out of the back


plate


of the


source


canister.


Finally,


Figure


shows


a proposed


two-orifice


lens


system


focus


ions


quadrupoles.


Because


clustering


was


such


problem


in the early


sources,


because


it is


clear what


portion


clustering


was


occurring


thermodynamic


cooling


post-orifice


supersonic


expansion,


therefore


desirable


prevent


Sciex


water


uses


a similar


sample

r system


molecules


from


entering


pressurizes


into

the


this

region


region.

between


two apertures


with


a relatively


inert


such


as carbon


dioxide


nitrogen


act


"ion


window"


which


transparent


ions


(because


of potential


fields


which


pull


the ions


through


this


gas)


restrictive


non-ionized


species


sample


which


might


clog


the orifice


or cluster


with


ions


in the


post


orifice


region.


In ion mobility/mass


neutral


spectrometry,


it is


such


common


to have


nitrogen


a backstream


helium


prevent


particulate


matter


from


reaching


the orifice


so this


idea


not


entirely unique


to the Sciex


instrument.


Thus,


was


felt


that


such


IS


nonreactive


,34]


m


1


I








to keep


neutrals,


except


nitrogen


molecules


small


amounts


impurities


from


the nitrogen


supply,


from


entering


the post-orifice


region.


Therefore


, to


provide


this


backstream


nitrogen


, a two-


orifice


system


was


designed


that


could


pressurized


with


nitrogen


gas.


would


flow


out into


the atmospheric


region


of the


source


also


into


vacuum


region


mass


spectrometer.


first


orifice


was


a 500


aperture


drilled


into


a stainless


steel


plate.


This


plate


served


to contain


nitrogen


possibly


provide


some


focusing


ions


electrically


"floating"


relative


ground.


maj or


interface


between


atmospheric


pressure


source


region


vacuum


region


mass


analyzer


was


thin,


replaceable,


stainless


steel


diaphragm


with


laser-drilled


orifice


(20-100


pm diameter)


obtained


from


Precision Aperture


[37]


skimmer


cone


lenses


were


designed


to focus


ions


to divert


excess


away


from


axis


of the


mass


analysis


system


so that


could


more


easily


pumped


turbomolecular


pump


normal


source


region.


region


after


the orifice


before


first


conical


lens


(hereafter


referred


the post-orifice


region)


at relatively


high


pressure.


Shahin


in 1965


noted


the ability


perform


some


declustering


background


water


clusters


accelerating


the ions


through


this


region.


Fite


in 1971


Levy


1984


noted


effect


of multiple


collisions


in a supersonic


thermodynamic


cooling


molecules.


Sciex


applied


similar









energy


spread


This


can


done


creating


potential


difference


between


the diaphragm


first


conical


lens.


If this


potential


difference


sufficiently


large,


can


enough


kinetic


energy


clusters


that


have


formed


cause


collisional


declustering


with


neutral


molecules


in the


supersonic


expansion.


This


ability


should help


reduce


clustering


in the


mass


spectra.


Potentials


provided


fellow


a power


research


idditiona

supply


group


lenses


designed


member.


Finnigan


constructed


voltages


system


Mark


these


were


Hail,


lenses


are


adjustable


by means


ten- turn


potentiometers


from


to 225


V and


monitored


a 3-1/


digit


display.


Source


Confi duration


Finniean


4500


Unfortunately


, discharging


first


orifice


was


not


possible


with


that


lens


floated


because


lens


power


supply


described


above


not


between


provide


the needle


lowest


path


output


another


resistance


impedance.


surface


ground.


When


a discharge


the current will


Thus


seek


power


is created


to follow


supply


this


floated


orifice


would


need


a very


output


impedance.


If the


power


supply


situation


circuitry


can


does


occur


of the


not


have


in which


mass


output


current


spectrometer


seeking


impedance,


passes


a path


through


destructive


electronic


to ground,


this


result


damage


circuit


components.


Sinc e


such


a power


are


[34] .
























0 I







I 1J
= *


I I




' "


II

Cu
QC
Cr)









(circumventing


need


additional


power


supply)


early


studies,


lens

the


a cage


to mimic

problem


electrode


the lens


was


system


orifice


inserted

of the old


clogging


in place


Finnigan API


cluster


of the second


source.


formation


conical


solve


flow


nitrogen


was


directed


stream


from


tube


placed


near


orifice


parallel


plane


diaphragm.


This


design


significantly


reduced


the frequency


of orifice


clogging


when


performing


direct


atmospheric


monitoring.


Source


Configuration


Finniean


interface


this


source


system,


several


modifications


were


made.


Figure


2.4 shows


a schematic


of the


current


source


complicated


design.


This


one-orifice


configuration


system.


However,


again


in this


incorporates


design,


less


seat


the diaphragm


been


machined


directly


into


a standard


iso-K


flange


which


a standard


vacuum


flange


the instrument.


This


flange


divided


into


sections


with


inner


section


(which


contains


diaphragm


seat)


having


electrical


vacuum


isolation


from


outer


ring.


outer


ring


clamps


directly


onto


the TSQ


vacuum


manifold


makes


interchanging


sources


relatively


easy.


first


conical


lens


(CL1


in Figure


2.4)


is mounted


on the flange


with


the diaphragm


seat


The


second


conical


lens


(CL2)


, a lens


directly


behind


(the


back


lens),


cylindrical


lens,


three


pre-quadrupole


focusing






























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normal


EI/CI


source


mounting


plate


associated


lenses.


These


lens


assemblies


can


be switched


loosening


two alien


screws.


source


canister


associated


lens


system


have


been


designed


totally


interchangeable


with


related


Finnigan


components.


Indeed,


the instrument


can


be changed


over


from


its normal


EI/CI


operating


configuration


an API/MS/MS


system,


evacuated,


running


system


about


to be later


minutes.


developed


This


for possible


increases


field


potential


work.


most


recent


addition


source


configuration


development


a current-regulated,


high


voltage


, low


current,


corona


discharge


power


supply.


This


supply


capable


producing


"true"


(stable


invisible)


corona


discharges


5000


with


currents


in the


range


of 0


Figure


a schematic


this


power


supply


with


the appropriate


components


labeled.


system


is centered around an


EMCO


to 6


kV adjustable


high


voltage


dc-dc


converter.


current


from


the discharge


is monitored


used


feedback


loop


to regulate


input


voltage


into


the dc-dc


converter.


Current


voltage


are adjusted


with


two ten-turn


potentiometers.


required


different


voltage


environmental


generate


factors


particular


such


current


as the composition


depends


of the


upon


near


discharge


needle,


flow


rate


past


needle,


needle-to-orifice


distance.


environment


changes,


the voltage


changes


converter


keep


reaches


current


voltage


constant.


limit,


However,

system


dc-dc


will


become


was


I


I _








































































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large


drop


current


will


occur


prevent


erratic


possibly


dangerous


discharge


from


ensuing.


Figure


schematic


power


supply


electrically


floating


orifice


from


+500


based


EMCO


dc-dc


converter.


This


a low


output


impedance


power


supply


that


adj stable


by means


a ten-turn


potentiometer.


parts


of this


source


(except


the normal


Finnigan


pre-quadrupole


focusing


lenses)

orifice


including


potential


power


were


supplies


designed


for the


this


corona


discharge


laboratory


constructed


in the University


of Florida


Chemistry


Department


machine,


electronics,


glass


shops.
















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CHAPTER


EXPERIMENTAL RESULTS


SOURCE


DEVELOPMENT


Results


with


Finnisan


API Source


4500


Mass


Configuration
Spectrometer


stated


in Chapter


the API


source


canister


was


designed


slide


through


a modified


conflat


flange


into


vacuum


region


Finnigan


4500


single


quadruple


mass


spectrometer.


While


this


design


allowed


source


compatible


with


Finnigan


instrument,


it caused


several


problems.


source


was


designed


modular


construction


that


design


changes


could


made


selected


parts


assembly


without


need


re-machine


entire


source


for each


modification


made.


Unfortunately,


at each


junction


between


individual


parts


of the


source


canister,


there


existed


potential


leaks


from


atmospheric


pressure


source


region,


of the


through


mass


junctions


spectrometer.


in the assembly,


source


was


into


designed


vacuum


so that


region


the orifice


plate


was


electrically


isolated


from


source


canister


initial


design,


a second


orifice


flange


was


to be inserted


between,


electrically


isolated


from,


these


two flanges) .


This


concept


was


to be


used


later


in electrically


floating


this


flange.


Electrical


isolation


accomplished


means


of placing


am anodized


aluminum,


ring-shaped


spacer


between


these


two components.


Vacuum


integrity


was


maintained


was


was








assembly


was


held


together


with


nylon


screws.


Because


large


force


of atmospheric


pressure


pushing


on the orifice


flange


nylon


screws


could


induce


a sufficient


counter


pressure


to maintain


vacuum


obtain


integrity.


vacuum


nylon


integrity


screws


some


were


degree


replaced


(although


metal


the metal


screws


screws


not


allow


electrical


isolation),


pressure


analyzer


region


of 1


x 10"


torr


was


eventually


obtained


for a 20


diameter


orifice.


To calculate


the expected


pump -down


pressure


an aperture


this


size,


fluid


dynamics


can


applied


treat


each


stage


differential


pumping


separately.


conductance


(Cvisc)


a 20


diameter


orifice


at atmospheric


pressure


can


be obtained


from


equation


below


[41].


Cvisc


- 76.6


x 50.712


where


- (P2/P1)


(where


are


the respective


pressures


either


side


orifice)


A is


the surface


area


of the orifice


cm2).


then


Cvisc


approaches


limiting


value


in equation


Cvisc


- 20 xA,


in Ls


A 20


pm diameter


orifice


a surface


area


x (1-60.258)0.








Thus


, for this


system,


Cvisc


- 20


cm2)


gas throughput,


qpv,


can


be defined


as in Equation


= Cvisc


x (P1


in torr'Ls


Substituting


Cvisc


torr,


making


approximation


that


throughput


found


torr' Ls


With


as defined


above


s as the pumping


speed


of the


first


turbomolecular


pump


(330


expected


pump down


pressure


first


region


differential


pumping,


can


found


from


equation


" qpv/


- (4.8


x 10"


torr Ls


- 1.5


torr.


Applying


this


calculation


again,


now with


x 10-4


torr


with


an aperture


radius


(for


aperture


between


the first


second


vacuum


chambers)


, r, of approximately


the expected


press


sure


second


region


differential


pumping


7 torr.


Although,


in the calculations


above


the nominal


pumping


speeds


for the


turbomolecular


pumps


were


used


effective


pumping


speeds


somewhat


less


(because


restrictions),


failure


c


are


Ls-1),


x 10-5


x 10-6


10-2


-1)/330


x 10-4









Nevertheless,


even


though


vacuum


integrity


source


poor,

first


these

ions


pressures

generated


were

with


sufficient


this


to perform mass


source,


spectrometry.


one-orifice


ground


potential)


system


with


no nitrogen


jet,


were


cluster


ions


of the form


H(H20)n


- 21


(m/z


109)),


(CH3)


2COH(H20)n


(m/z


= 4


113)


(m/z


189)] ,


(m/z


203)],


generated


(CH3)2COH


inducing


(H20)n


a flow


(m/z


of laboratory


153)


past


the discharge


region


(Figure


acetone


ions


are


from


residual


solvent


left


after


source


cleaning,


which


vaporizes


source


walls


diffuses


discharge


region


because


lack


nitrogen


jet.


These


ions


were


very


intensity,


the lack


cluster


ions


with higher m/


values


probably


results


from


a lens


tuning


effect.


Without


the nitrogen


or an electrically


floated


orifice,


this


source


configuration


only


limited


abilities


declustering.


Figure


shows


the resulting mass


spectra


(all


normalized


to the


same


intensity)


when


the potential


difference


between


grounded


orifice


the first


conical


lens


was


changed


from


to 8


While


the effect


not


dramatic


slight


decrease


cluster


ions


with


higher


values


relative


to those


with


lower m/z


values


apparent.


However,


stream


even

direct


when analyzing vapor


t


atmospheric


samples


monitoring)


injected


into


clustering


was


a nitrogen


still


problem.


Figure


3.3 (a)


- (c)


shows


mass


spectra


obtained


representative


compounds


which


undergo


charge


exchange


ionization


was






































































































A;TSUafUI


"









Potential


Difference


Potential


145 1


Difference


433


Potential


127


Difference


(d)


Potential


Difference


IC3 260 3C9 4C 503


Figure


































Figure


API/MS o
nitrogen


f compounds


stream


that u
carbon


ndergo


charge


disulfide


exchange i
) benzene,


.onization


in a pure
toluene.


, (b











Carbon Disulfide
MW = 76


50.8-










ICT.L -





50.0


Benzene
MW = 78


Toluene
MW = 92


I


I









cluster


ion.


Benzene


toluene


form


both


the Mt


molecular


the M2+


cluster


ions.


Figure


shows


mass


spectra


obtained


representative


compounds


which


undergo


proton


transfer


ionization


in the API


source


acetone


, ethyl


acetate


and methanol


, respectively.


Acetone


ethyl


acetate


form


both


the (M+H)+


pseudo-molecular


(M2+H)+


cluster


ions.


ions


formed


from


methanol


display


severe


clustering


are of the form


[M+H(H20)n


- 5),


- 2),


0)n]+


(M4+H)+


Adaptation


of the


Source


to the


Finnigan


70 Mass


Spectrometer


70 Characteristics


This


which


mas s


have


spectrometer


proven


some


beneficial


unique


performing


characteristics,


source


most


development


This


valves


instrument


, pumps


almost


heaters


totally


and most


under


importantly


microprocessor


lenses


control.


quadrupoles


control


"firmware"


(program


code


stored


erasable,


programable


read-only


memory


(EPROM)


chip


which


accesses


single


board


minicomputers


sophisticated


tuning


located


instrument.


optimization


performed


This

with


allows

relative


ease.


instrument


differentially


pumped


turbomolecular


spectrometry


pumps


in less


, which


than


can


reach


15 minutes


(with


vacuum


suitable


additional


mass


loads


can


.....


[M2+H(H20)n]+


M3+H(H


k


I


..


I


V&&


































Figure


API/MS


nitrogen


of compounds


stream


that undergo


acetone


, (b)


proton
ethyl


transfer


acetate


ionization


, and


a pure


methanol.









117 (M2+H)+


Acetone
MW = 58


(M+H)


Ethyl
MW


Acetate
= 88


(M+H) +

\


(M2+H)+


Methanol
MW = 32


nM+H(H20),]+
[M,+K(HO) ni]


<1>


n 2, 3, 4, 5 n
n -a 0, 1. 2


[M3+H(H20n,] n 0, 1





(M4+H) *
/









differentially


suitable


vacuum.


pumped


flanges


analyzer


sections)


instrument


to maintain


are


standard


diameter


iso-K


flanges


which


clamp


onto


the manifold


using


an o-ring


between


the flange


the manifold


to maintain


vacuum


integrity.


lenses


quadrupoles


are


mounted


optical


rail


easy


maintenance


(and


in this


case


easy


modification)


are each


held


place


only


one or two screws.


normal


EI/CI


source


lens


assembly mounts


to this


optical


rail


in the first


differentially pumped


chamber


mass


spectrometer,


removable


loosening


allen


screws.


Source


Modifications


Optical


Modeling


order


interface


source


canister


vacuum


manifold,


a new


adapter


flange


was


needed


to replace


the conflat


flange


compatible


with


the Finnigan


4500.


Since


vacuum


ports


on the


vacuum


manifold


used


iso-K


type


flanges,


was


necessary


base


the adapter


flange


on this


standard.


With


the freedom


to design


new


flange,


was


also


decided


alter


the design


source


reduce


the problems


with


vacuum


integrity.


This


modified


source


design


moves


junctions


between


source


parts


outside


vacuum


manifold


mas s


spectrometer


machining


diaphragm


seat


directly


into


iso-K


flange.


Thus


the only


possible


locations


leak


are


knife-edge


seal


orifice


o-ring


between


normal


iso-K


ins trument


flange


configuration)


vacuum


The


rest


manifold


(which


of the canister


attaches


Lon source


Vacuum


two









(such


that


from


a can


common


laboratory


freon,


from


compressed


nitrogen,


or air)


can


be used


to clear


the blockage.


Later


flange


was


re-designed


that


final


configuration


divided


into


two concentric


sections


the inner


section


(containing


diaphragm


seat)


being


electrically


isolated


from


outer


section.


test


a 70


vacuum


diameter


earlier


this


integrity


orifice


was


chapter,


of this


installed.


theoretical


source,


Using


pump- down


a diaphragm


containing


equations


pressures,


found


for the


first


second


differentially


pumped-re


ions


of the


mass


spectrometer


are calculated


to be 1.8 x 10-


torr


x 10-6


torr


, respectively.


actual


pump-down


pressures


were


found


to be


10-3


Therefore


appears


that


this


interface


serves


maintain


vacuum


integrity.


optical


modeling


program,


SIMION


, that


been


modified


run


on a PC/AT


microcomputer


was


used


to model


lens


system


the API/MS/MS


instrument


configuration.


This


approach


proven


system


advantageous


interfacing


the

API


design


source


and

ithe


development


mass


spectrometer.


lens

Two


examples


of the


use


of this


program


are given


below,


although


it should


be pointed


out


that


this


program


does


not


take


into


consideration


multiple


inelastic


collisions


that


ions


incur


relatively


high


pressure


post-orifice


region.


Therefore


, the actual


lens


voltages


used


for maximum


transmission


can


very


different


from


the values


that


give


best


transmission


the collision-force


model


used


was








physical


design


lenses


themselves,


rather


than


predicting


actual


lens


potentials.


To simplify


system


facilitate


testing,


source


been


used


in the one-orifice


configuration.


characteristic


mass


spectrometer


which


turned


disadvantage


adaptation

electrically


source


grounded


source


mounting


mass


plate.


spectrometer


Since


the API


was


source


been


installed


front


mass


spectrometer,


this


grounded


plate


resides


between


the API


source


mass


analyzer.


This


plate


holds


normal


EI/CI


source


assembly,


including


pre-


quadrupole


lenses


Since


positioning


these


pre-quadrupole


lenses


is critical,


was


desired


use


this


same


mounting


plate


with


a modified


lens


block which


held only


the pre-quadrupole


lenses


and had


excess


in this


metal


mounting


removed.


plate


Unfortunately,


through


there


which


is only


generated


a 3/4"


ions


aperture


are to be


focused.


Figure


shows


the SIMION


representation


of the


lens


system


for the API


source


interfaced


to the TSQ


mass


spectrometer.


Figure


shows


equipotential


lines


on each


lenses


lens


mounting


block.


Because


lens


mounting


plate


electrically


grounded,


relatively


energy


positive


ions


which


enter


even


slightly


off-axis


are


repulsed


associated


field.


Figure


shows


trajectories


an ion


with


a m/z


value


of 181,


an initial


energy


of 0.2


, and


with


initial


angles


of 0


S10

































Figure


optic


modeling


of lens


configuration


for API


source


on TSQ


mass


spectrometer


showing


the representation


of this


lens


system with


SIMION


program,


with


potential


contours


values


more


positive


than


lens


voltages),


with


representative


trajectories











Orifice
Plate


Lens
Mounting
Plate
I


tIIlIIIIJ


Lens
Block


Pre-Quadrupole
Lenses


"II

"ll~II~ l' I


-160


GRND


GRAND


GRND





























Figure


optic


modeling


of lens


configuration


for API


source


on TSQ


mass


spectrometer with


the addition


of a cylindrical


lens


showing


representation
equipotential


lens
(d)


potential)


with


of this
contours


, (c)


lens


(for


with


representative


system with
potentials


representative
n trajectories


the SIMION


more


program,


positive


trajectories
-30V.


with


than
-5 V,







Cyllndrlcai
Lens


I,,11 '


Lens
Mounti/
Plate


Lens
Block
V


rilmnnnlgtniliuin


Pre-Ouadrupole
Lenses


-160
04-
OI

II,


* I I I
I



i

it
I!
ui


GRND


GRND


GRAND


I


(d)


Orifice
Plate


fl..flsm ii









mounting


plate.


cylindrical


lens


Figure


shows


potential


the equipotential


This


improves


contours


transmission


ions


with


181,


initial


energy


of 0


initial


angles


20 degrees


center


axis.


With


this


potential,


ions


degrees


center


axis


are


focused


through


the lens


system.


In Figure


the potential


on the cylindrical


been


increased


-30 V.


plotting


traj


ectories


for ions


with


same


initial


conditions


above


can


seen


that


ions


with


initial


angles


degrees


center


axis


are focused


through


the lens


system


the quadrupoles.


To aid


in the


focusing


of ions


the pumping


of the


excess


gas,


a second


conical


lens


(CL2)


was


added


design.


order


implement t

cylindrical


SIMION


his

hole


program


lens


a focusing


is required


was


used


directly


to model


lens


element


behind


the effect


the


, a plate

2nd conical


of the


aperture


Lens


with


lens.


size


lens


(the


back


lens)


, immediately


behind


on the focusing


of ions


(now with


a higher


energy


- 10 eV)


after


being


accelerated


through


first


conic


lens)


through


into


cylindrical


lens.


Figure


SIMION


representation


a portion


lens


assembly


consisting


of CL2


the back,


cylindrical


lenses


with


potentials


, and


-150


respectively.


Figure


(b)-


shows


effect


small


(0.25"


diameter),


medium


.50"


diameter)


large


.75"


diameter)


apertures


on ion


trajectories


ions


with


initial


angles


, 15,


degrees


























O )

Cn
U C: 00
0Z 0


c Q
~O 0.
b0 (U
bC 0
-* -f

4J
0


0 r0 C 0


CO O)0
K C rb ar r -1


00 U *C
1M< Tt 'r Ij
aa.-.


,C C
( 40 r C

5 9 <


0 4J G
ou eta

0 0
0 M
C tn C
0 co M &.--













- am
- am


212


- -. .


L ^
co -
I-(
s/-


caa





mmI 1

-I I
~mi





aim
-h
-2


~IL
-i, i


,It
i. i i I .


a


man


m m






I -

---ta--'!! i!/l --
-V
mm






H J


f I
- ap4
- a


-,-
-.


Ii
i!
________ :i!!
_____ i


-~"*
-


*m a










-- a___
a- ------
-m am
Swm
a -


S* -"
0) -__


5a
a,3
ae

a


pj
-'I1


Ii;



Si i



,ii

i t


- -
a
a
a

a


I,1

II
I I i


iii
I,




i-


,clr


b


--L1I*~4


)-.C- am-mmmlm


C. V
U Cb .
F er


P3-J









large


apertures


this


value


improves


to 20 and


25 degrees,


respectively


However


, if


this


back


lens


removed


completely


(not


shown)

cause


the potential


sufficient


field


convergence


the cylindrical


of the ions


lens


to allow


not


capable


transmission


through


the pre-quadrupole


lenses.


re-design


of the


source


with


a new


adapter


flange


the SIMION


program


to model


lens


system


proved


advantageous


developing


operable


source.


moving


junctions


between


source


canister


parts


outside


of the


vacuum


system,


it became


practical


. to


use


diameter


orifice.


optical


modeling


saved


much


effort


time


developing


two new


lenses


for the


system,


a cylindrical


lens


to penetrate


the potential


field


generated


the grounded


source


mounting


plate


the optimum


aperture


size


for the


lens


immediately


following


CL2.


Flows


Using


equations


presented


earlier


this


chapter,


conductance


(Cvisc)


diameter


orifice


calculated


.7x10"4


46.2


mL-min


measure


rate


flow


through

the exhai


the orifice

ust port of


a common


laboratory


the mechanical


backir


bubble

ig pump


metel

for


:r was

the t


hooked


:urbomolecular


pumps.


Since


one


mechanical


pump


serves


the backing


pump


for both


turbomolecular


pumps


, any


gas


that


enters


system


must


exit


through


this


port.


With


the orifice


pm diameter)


plugged,


the flow


rate,


1


mL*min


When


the orifice


was


unplugged,


this


flow rate


a


use


was









error


(the


actual


size


of the orifice


is 70


pm 10%)


the calculated


conductance.


measurement


flow


rate


through


glass


tube


used


direct


atmospheric


sampling,


bubble


meter


was


modified


such


that


was


drawn


through


the bubble


meter


attaching,


with


flexible


tubing,


bubble


meter


the glass


sampling


tube.


Both


orifice


sampling


served


draw


air


through


sampling


tube.


Because


the flow


rates


through


the orifice


through


sampling


are


fixed,


additional


loads


would


reduce


flow


through


sampling


tube.


With


no flow


for the


nitrogen


jet,


sampling


flow


rate


was


found


to be


77.4


mL min


With


nitrogen


flow


was


found


74.8


mL'min


Therefore,


flow


rate


nitrogen


(flowing


out


of a 1/16"


tube)


was


mL"min


This


common


configuration


instrument


while


performing


direct


atmospheric


analysis.


-Discharze


Power


SuDolv


stated


second


chapter,


dischar


power


supply


which


was


used


most


this


work


was


a Bertan


205A-05R


voltage-


regulated


power


supply.


discharge


from


which


ions


were


detected


(with


this


power


supply),


was


visible


(violet


color)


unstable


varying


degrees,


a current


produced


an ion


signal


which


was


extremely


unstable


noisy.


erratic


times


would


this


change


discharge


a bright


would


white


become


color.


very


Since


power


supply


regulated


the voltage


, any


change


in resistance


in the


was









change


intensity.


Tuning


was


performed


scanning


much


slower


rate


s/scan)


than


normally


required


for quadruple


mass


spectrometry


still


was


at best,


difficult.


true


corona


discharge


invisible,


stable


much


lower


current


than


discharge


obtained


above


[341].


second


chapter


discusses


power


supply


that was


designed


built


to generate


such


a discharge.


corona


discharge


obtained


with


this


current-regulated


power


supply


meets


aforementioned


requirements,


with


a stable,


selectable


current


of 0


to 4.5 pA.


voltage


required


to produce


corona


discharge


is dependent


on the


current


desired,


the flow


rate


composition


gases


discharge


region,


needle-to -


orifice


distance,


usually


was


on the order


of 3


to 4.8


With


this


stable


discharge


the ion


signal


was


significantly


less


noisy


, and


therefore


, tuning


could


performed


with


automated


tuning


procedures


at a much


faster


rate.


Orifice


Potential


With


electrically


present


grounded


design


possible


floated


500


have


orifice


low- impedance


power


supply


(see


Chapter


Initial


experiments


were


performed


with


orifice

directly


placed


at instrument

Instrument z


ground


manifold.


connecting


Later,


its electrical


improve


lead


sensitivity,


the orifice


was


electrically


floated at


to +150









ExPerimental


Physical


Parameters


of API Source


and Mass


Spectrometer


Initial


Enerev


Enerzv


Spread


An experiment


was


set up


such


that


intensity


of the ions


generated


the API


source


was


monitored


the voltage


on the second


conical


lens


(CL2)


was


varied,


while


keeping


orifice


ground


potential


the first


conical


lens


(CL1)


-4.4


V relative


to ground.


Figure


"stopping-potential


curve"


a plot


intensity


(scale


left-hand


axis)


vs.


potential


lens


(with


a potential


of CL1


- -4.4


together


with


the first


derivative


this


curve


(intensity


scale


right-hand


axis)


first


derivative


provides


potential


that


will


stop


an ion


with


average


kinetic


energy


the


peak


first


derivative


curve)


kinetic


energy


spread


the ions


the peak


width


half height).


A simple


numerical


method


was


employed


to find


the first


derivative,


relative


plotted


which


difference


. the


average


difference


consecutive


of their


consecutive


axis


corresponding


axis


values


pair


(Ay/Ax


x axis


values


was


values.


difference


curve


that


was


generated


yielded


values


-3.8


V and


eV for


the potential


required


stop


an ion


with


average


kinetic


energy


the ion


kinetic


energy


spread,


respectively.


Since


the orifice


at 0.0


V (ground


potential)


the first


conical


lens


-4.4


positive


ions


were


analyzed,


the ions


should
































































































) 0
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4- CO






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(,A/s unoz) |DIILuJ aNI


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it


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"stop"


ions


(i.e.


decelerate


ions


energy).


A simplistic


model


for this


system


is displayed


in Figure


(a).


ion,


transversing


the potential


field,


can


be thought


as a


ball


rolling


down a


slope.


If the ball


is released


down


the slope


from


resting


position


will


accelerated


gain


kinetic


energy)


to gravity


falling


some


height,


therefore


it will


take


height


equal


to h


to decelerate


the ball


(reduce


kinetic


energy)

indicate


until


stops


situation


more


again.

like


The

Figure


experimental


(b),


results


in which


seem


the ball


stopped


a slope


that


is only


a fraction


of the initial


height;


that


takes


a smaller


decelerating


energy


than


expected


to stop


ball.


Barring


other


factors


if the ball


were


released


from


same


initial


height


in Figure


should


stopped


opposite


(c)).


slope


Likewise,


should


barring


continue


other


on out


factors


, the


system


would


(Figure


be expected


pass


through


stopped.


decelerating


experimentally


field


determine


provided 1

ad voltage


needed


instead

to stop


of being

the ions


found


to be


-3.8


deceleration


of 0.6


eV from


the CL1


to CL2


lenses)


therefore,


the ions


must


have


been


accelerated


only


0.6 eV


on their


the first


conical


lens


This


could


occur


if the ions


were


generated


at a potential


field


more


positive


than


that


the first


conical


lens


(i.e. ,


at -3.8


V with


respect


to ground).


This


is analogous


to the ball


starting at


a very


height.


However


, it is


known


that


formed


on the


atmospheric


side


orifice


, it


was









62




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energy


where


was


being


the friction


retarded.


was


large


ball


the ball'


was


rolling


acceleration


down


would


surface


slowed


friction;


that


friction


would


retard


ball


from


increasing


kinetic


energy.


post-orifice


region,


supersonic


expansion


occurs


the ions


molecules


from


atmospheric


side


orifice


vacuum


side


orifice.


Since


high


near


pressure


(several


the ions


mtorr)


and molecules


, the


bulk


are still


at a relatively


undergo


1 thermodynamic


cooling


their


translational


energy


through


multiple


collisions


with


each


other


supersonic


expansion


39].


ions


exit


the orifice


, they


are


translationally


cooled


along


with


bulk


molecules


inelastic


collisions


ions


have


with


translationally


cool


molecules


also


allows


rotational


vibrational


motion


of the ions


to be transferred


to the translationally


cool


molecules.


Thus,


the ions


experience


the full


accelerating


potential


field


because


of collisional


energy


exchange


with


more


abundant


neutral


molecules


which


remain


unaffected


potential


field.


Further


downstream


in the jet,


the number


of collisions


between


ions


the molecules


decreases


this


collisional


cooling


longer


occurs


Figure


.10 is stopping-potential


its associated differential


curve


(plotted


(plotted on


on the left-hand


the right-hand


determined


with


electrically


floated


orifice


with


potential


+120


with


potential


+81.9


the orifice


molecules


axis


axis)












(A/s unoo)


I oD !m JJ aJ1Q


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0 0 0
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0 0 0
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o Un o


(000 l/swunoo)


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approximately


10 eV


Because


it required


only


to decelerate


average


to rest,


the ion


therefore


could


only


have


been accelerated


from


orifice


despite


38.1


potential


difference


between


these


components


these


higher


voltages


however


, there


a much


greater


spread


in the ion


energies.


Needle-to-orifice


Positioning


For a discharge


provided


a voltage-regulated


power


supply


position


of the needle


was


critical


the production


even


a semi-


stable


discharge


the number


of ions


which


were


detected


mass


spectrometer.


Figure


(all


dimensions


inches)


schematic


representation


of the needle


position


relative


to the orifice


orifice


plate


which


greatest


intensity


ions


were


obtained.


Characteristically,


the discharge


was


formed across


the face


of the orifice


the opposing


sharp


edge


of the orifice


plate.


When


the needle


was


moved


across


the face


of the orifice


towards


center


axis


orifice


(Figure


3.11


intensity


decreased


rapidly


the needle


zero.


A semi-stable


in towards


the orific


discharge

e (Figure


was

3.11


also

(c))


obtained


however,


moving


no ions


were


detected


mass


spectrometer


this


needle-to-orifice


position.


Since


positive


whatever


ions


surface


the needle


will


is serving


at a large


repelle

as the


positive


from


counter


electrode.


potential


celebrated

When th


4000


towards


xe needle


the position


in Figure


3.11


(a),


ions


that


are


created


region between


the needle


center


axis


of the orifice


can


, the


(b)),



































Figure


Schematic
relative


representation
to orifice. P


(not


)sition


to scale,
which g


1/8"


generates


of needle position
a discharge across


face


orifice


from


which


ions


are


detected,


a discharge


similar


detected,


shorter


a discharge


in length ar
to the orifice


which


ions


are

















e. 85


8. 11


8.99


6.85


8.88


e.88


(a)










(b)










(c)


.88


8.89








repelled


into


the diaphragm


or into


source


mounting


plate


will


be directed


through


the orifice.


Likewise


if the needle


is moved


towards


orifice


discharges


orifice


potential


field


lens


system


will


not


strong


enough


direct


ions


through


the orifice


because


the field


generated


the discharge


needle


will


very


strong


in this


region


the close


proximity


needle


to the grounded


surface.


an electrically


floated


orifice,


the position


of the needle


the needle-to-orifice


position


critical


case


above


production


stable


discharge


detection


ions.


Factors


that


affect


discharge


voltage


required


produce


a selected


current


include


flow


rate


composition


in the discharge


region,


the potential


orifice,


needle-to-orifice


positions.


Because


limited


output


voltage


dc-dc


converter


needle- to-


orifice


distance


required


to maintain


a discharge


is limited


to only


few millimeters.


However,


within


this


range


this


discharge


obtainable


always


stable


(unless


needle


was


shorted


surface


of the orifice


plate).


Effect


of Various


Parameters


on the Ethyl


Acetate


Family


While

a positive


orifice,


the potential


potential


also


field


causes


increases


from


electrically


a greater


energy


floating


transmission


of ioi


spread


the orifice

ns through


ions.


ions


with


a very


small


amount


of kinetic


energy


can


cluster


in the


post-orifice


region.


Ions


with


a large


amount


of kinetic


energy


(>7-


not


are


not


was


eas








declustered


form


molecular


(M +)


or pseudo-molecular


(M+H+)


ions


343.


When


ethyl


acetate


- CH3CO


CH2CH3)


is ionized


in the API


source


ions


with m/z


values


of 177 (M


+H +)


[M+H(H20)2+


(M+H30+)


(M+H+)


, 61


(M+H+


- C2H4),


H5+)


are detected.


Because


kinetic


energy


spread


, both


cluster


ions


(m/z


107)


fragment


ions


(m/z


61 and


are


present


with


the pseudo-molecular


(m/z


89).


It is desirable


to limit


the production


of both


cluster


fragment


ions


to increase


amount


the pseudo-molecular


that


is detected.


Therefore


the orifice


potential


the potential


of the


first


conical


lens


were


varied


intensities


of members


of the


"ion


family"


ethyl


acetate


z 177, 107,


were


plotted


these


values.


Figure


3.12


shows


intensities


of these


ions


plotted


(m/z


shown)


vs.


orifice


potential,


while


holding


the potential


of CL1


at +40


At approximately


100 V (a


V potential


difference


in the


supersonic


expansion


region)


greatest


ions


potential


intensity


achieved.


difference


of m/z


lower


between


relative


values


the orifice


intensities


orifice


CL1)


of the


potential


clustering


other


(lower


increases,


higher


values


(higher


potential


difference)


fragmentation


increases.


These


same


ions


are plotted


vs. the potential


of the first


conical


lens


while


holding


the orifice


at 100 V in Figure


greatest


intensity


relative


intensities


other


ions




























0


0~
*



60
Q ^
Co
"O


do
OOj


r r. r.


0
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(s;unoo)


0
o re
o
o
ON


A^Is ua^ul

























01
Co
N
E 9
NO


1p


0 |s
o 0
o C,


02
0 C
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:0


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C
0

ndJ
M u
U)


<- 0
o *


*0

0P


(s;unoo)


A;!S U&;ul








tons


increase


steadily


in intensity


until


a potential


of about


70 V


the conical


lens


at which


time


the intensity


of the fragment


ion,


drops


off.


other


ions


increase


intensity


until


approximately


when


intensities


ions


begins


decrease.


It is apparent


that,


with


the floated


orifice


both


clusters


fragments


will


observed


because


kinetic


energy


spread;


however


this


seems


to be


a worthwhile


tradeoff


the increase


intensity


that


the floated


orifice


provides.


intensities


of members


of the ion family


of ethyl


acetate


(m/z


177,


107,


were


plotted


relative


discharge


current


(Figure


determine


what


effect


current


upon


processes


clustering


fragmentation,


well


intensities


ions.


From


these


data,


appears


that


highest


intensities


ions


the highest


ratio


the pseudo-


molecular


intensity


that


of the cluster


fragment


ions


occur


regions,


from


from


lowest


discharge


current


that


can


is 0


because


below


this


value


it becomes


very


difficult


to regulate


current.


Between


1.2 and


the intensity


of the protonated


dimer


increases


significantly,


while


intensities


intensities


other


of all the ions


ions


decrease


decrease.

rapidly.


Above al

Currently,


bout


the effect


current


relative


intensities


these


ions


understood.


two


not















































-o
- .0
I-


- . S SSai lai SI ST I N I


* I


S S I *


S N I


ITlillIll
j I I I I I l l i l l l I I I I I I I I I


Si l


t1 IlI


O
0
0
0
+
O
O
0
*


(sCunoo)


A isua ul


qn


N

E<


N
N


00
C
+
O
0
0


9-






74

Clusterine/Declustering


clustering


of ions


with


molecules


supersonic


expansion


post-orifice


development


region

API


source


been

for


one of the

direct a


maj or


problems


atmospheric


monitoring.


Indeed,


only


source


that


successfully


overcomes


this


problem


been


built


Sciex


25].


This


problem


can


minimized


three


ways.


first


to start


with


a sample


that


contains


no water


vapor,


such


effluent


from


a GC.


Unfortunately,


direct


atmospheric

A second


other


monitoring

method to


neutral


removing


reduce


impurities


water


clustering


from


vapor


is nearly


to prevent


entering


water:


post-orifice


impossible.

r molecules


region.


Sciex


accomplishes


this


drawing


ions


that


are


formed


through


pre-orifice


region


(enclosed


aperture


plate,


which


dischar


is struck,


the orifice


plate)


which


been


pressurized


(slightly


carbon


pumping)


referred


this


atm)


dioxide


or nitrogen


this


instrument,


with


(for


(for


region

with


a pure


liquid


liquid


a "gas


a less


, relatively


inert,


nitrogen


helium


cryopumpab le


liquid


cryogenic


curtain"


complicated


helium


pumping).


"ion


window"


one-orifice


system,


such


cryogenic


Sciex


[33].


a gas


"jet"


been


produced


introducing


a gas through


aperture


1/16"


tube


positioned


near


the orifice.


With


an electrically


grounded


orifice,


this


appreciable


effect


amount


clustering


that


occurs.


Figure


shows


mass


spectra


water


one







75




(H20) nH+


- 4


i 53
129 23237 ?


S180 1SO 2B0 255 328 35


=4 -22





Z53
235

199 271
1 217 I


56 I S 150


Figure


20) nH









nitrogen


intensities


large


cluster


ions


are


reduced


while


intensities


small


cluster


ions


are


increased


orders


of magnitude


relative


to their


intensities


with


the nitrogen


off.


third


induced


method


declustering


reduce


clustering


in the post-orifice


perform


region.


Sciex


collision-


performed


this


applying


potential


field


this


region


impart


enough


kinetic


energy


allow


cluster


ions


occur


[34].


theinstrument


developed


in this


, this


same


effect


can


be observed.


Figure


.16 shows


mass


spectra


obtained


(orifice


potential


- +100


V and


a dry


compressed


air jet


flow


rate


of approximately


mL'min


for (a)


a potential


difference


between


the orifice


first


conical


lens


potential


difference


(both


mass


spectra


plotted


same


intensity


scale).


While


cluster


ions


with


large


values


are reduced


, the cluster


with


small


values


increased


factor


Furthermore,


with


a floated


orifice


a potential


difference


high


enough


cause


declustering)


appears


have


effect.


Figure


floated orifice


, respectively.


show


(potential


This


difference


same


mass


- 50 V)


effect


spectra


and a


observed


attained


nitrogen


sample


with


on and


cluster


ions.


Figure


.18 shows


that


having


on or (b)


off has


little


effect


spectra


obtained


when


ethyl


acetate


analyzed


direct


atmospheric


monitoring


this


source


with


a floated


are




















































































































0 o
- *C


* 0 0 0 <
* a is w i
ESes


A


























rCC




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.4




rH





wi"'"
w
i r


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'a .9 *


a-'


4-


A isu9}ul


_a









79







*h
"r


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IN N --
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-, U
-
e Ll








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o 0


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*1 0
e *











MA
rs rt r^

o P, o






UU
a -l *




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"ee
t a



e

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rs rl ir








'Ia- 0




a a


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00












--t W i


_ _____ $5__ 'U


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-** a .* *t -,
Ca'
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a 0 0 0 a0










4' 0*- <;
'4 2 '4 B
-4 -% I



AjISUQjuI









to employ


to prevent


orifice


clogging


to reduce


memory


effects.


Experimental


Methods


for Direct


Atmospheric


Monitoring


Mass


Calibration


of API/MS/MS


Instrument


order


instrument


employ


mus t


have


mass


spectrometer


accurately


assign


mass


analysis,


values


signals

tuning


it is obtaining.


a mass


This


spectrometer


process

usually


is called mass


refers


calibration.


the adjustment


of lens


quadruple


offset


voltages


that


maximum


intensity


obtained.


In the


case


of a quadruple


mass


spectrometer,


a calibration


compound


which


produces


ions


of known m/z


values


is analyzed


(for


EI/CI


this


typically


perflurotributylamine


(FC43))


calibration


table


then


generated


which


relates


the scanning


voltage


of the quadruple


to the


correct


value.


These


values


can


be compared


to the voltages


needed


pass


ions,


of otherwise


unknown


mass,


from


other


samples


calculate


their


values.


Although


mass


calibration


this


instrument


does


change


while


switching


between


installation


the need


of this


source


re calibrate


requires


re- tun(


a new

e for


lens

API.


system

Since


which


results


background


ions


abundant


in API/MS


water


cluster


ions


ions


were


detected


for FC43)


are


used


to calibrate


the ins tnrunent


perform


lens


tuning,


after


which


sample


gases


be analyzed.


can


be ascertained


from


are









calibration


proved


efficient


unit


mass


resolution


quadrupole


mass


analyzers.


SamDline Methodologe


vapors


analyzed by


direct


atmospheric


monitoring were


generated


drawing


across


caps


from


bottles


of liquid


compounds.


studies


which


required


a steady


concentration


sample


long


periods


time


(such


calibration


tuning),


drops


compound


were


placed


in the bottle


was


placed


in front


of the 1


diameter


glass


sampling


tube


of the API


source.


Although


vapor


pressure


liquid


samples


can


estimated,


amount


sample


introduced


not


accurately


known,


absolute


determination


API/MS/MS


instrumental


sensitivity


therefore


possible.


not









CHAPTER


ANALYTICAL


PERFORMANCE


evaluate


performance


analytical


instrument,


several


factors


considered;


however,


not


factors


are


necessarily


important


for all


types


instruments.


an instrument


which


performs


direct


atmospheric


analysis


these


factors


include


ability


instrument


identify


sample


analyzing,


the ability


of the


instrument


detect


trace


amounts


sample,


ability


instrument


to distinguish


between


compounds


in the


same


sample


, memory


interference


effects


analysis,


ease


instrument,


time


required


sample


analysis


(including


equilibration


time


between


samples).


Characterization


of an API/MS/MS


Instrument


Analyses


of Pure


Compounds


With


source


spectrometer,


configuration


clustering


proved


for t

such


:he Finnigan


large


4500

problem


quadruple

!m that d


mass


irect


atmospheric


monitoring


was


nearly


impossible.


Indeed,


even


solvent


vapors


inj ected


into


a pure


nitrogen


stream


displayed


cluster


ions


predominant


ions


design


detected


70 with


(Figures


a nitrogen


source


the instrument


can


be tuned


significantly


minimize


the clustering,


even


while


performing


direct


use


































Figure


Direct


exchange


atmospheric


ionization


monitoring/API/MS


carbon


compounds


disulfide,


that


benzene


undergo


, and


charge


toluene.












Carbon


Disulfide


MN


15115


enzen


92 +


Toluene


se 100


'-(a)









(with


grounded


orifice


a voltage-regulated


power


supply)


while


performing


direct


atmospheric


monitoring


representative


compounds


which


undergo


charge


exchange


ionization


source,


carbon


disulfide


benzene


toluene


, respectively.


These

carbon


compounds

disulfide


each


form almost


forming


a small


exclusively

amount of


the M+


the M2+


molecular


dimer


ion,


ion.


with


Figure


- (c)


shows


mass


spectra


obtained


(with


a grounded


orifice)


while


performing


direct


atmospheric


monitoring


representative


compounds


which


undergo


proton


transfer


ionization


in the API


source,


acetone


58),


ethyl


acetate


88),


methanol


32),


respectively.


Acetone


ethyl


acetate


both


form


almost


exclusively


the (M+H)+


pseudo-molecular


ion.


most


predominant


for methanol


(M2+H)+


protonated


dimer


ion.


While


the signal


obtained


under


these


mass


conditions


spectrometry


these


(MS/MS)


samples


these


was


not


results


sufficient


demonstrate


to perform


that


tandem


this


source can


reduce


clustering


significantly.


Figure


shows


the reconstructed


current


(RIC)


traces


for the


two most


predominant


background


ions


(when


the instrument


is tuned


large


amounts


declustering


analysis


performed


bringing


caps


of solvent


bottles


near


sampling


tube


of API


source)


(H20)2H+


(m/z


(H20)3H+


(m/z


, two representative


sample


ions


(CH3CO2C2Hs) H


the ions.


In normal


mass


spectrometry,


sample


ionization occurs


the bombardment


of the sample


molecules


with


electrons


from


filament.


positive


mass


C6H6+
































Figure


Direct


atmospheric


monitoring/API/MS


compounds


that


undergo


proton


transfer


ionization


acetone,


ethyl


acetate,


methanol.













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reagent


ions


are low in m/z


value


mass


spectrometer


pass


only


ions


a greater


mass.


Ionization


mass


spectrometry


occurs


a similar


fashion


to CI


mass


spectrometry


Chapter


In direct


atmospheric


monitoring


mass


spectrometry,


serves


reagent


(equations


- 1.5)


gas,


Sample


generating


molecules


can


H2O+


react


H30+


with


ions


reagent


ions


through


charge


exchange


or proton


transfer


reactions


form


molecular


M+H+


pseudo-molecular


ions.


kinetics


production


Ions


discharges


atmospheric


pressures


been


studied


atmospheric


water


Shahin


and Kebarle


sampling


vapor)


samples


production


H2O+


Shahin


with


stated


even


charge


that


a small


exchange


for direct


quantity


with


initial


case


ions)


of either


H30+


charge


ions


would


or proton


the dominant


transfer


ionization


reactions.


reactions


intensity


reagent


ions


reduced


sample


ionized.


Samples


that


undergo


proton


transfer


ionization may


totally


deplete


population


background


ions


while


samples


that


undergo


charge


transfer


ionization


reduce


not


deplete


that


population.


Figure


shows


relationship


between


intensity


reagent


ions


with


respect


time


allowed


reaction.


Equations


give


rate


constants


production


H20O


, H3O+


H(H20)n


+ H20+


1.9 x 10-9


cm3.molecule


(4.1)


can


see


[44].




















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