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NIOXIME-A REAGENT FOR NICKEL
By Roger C. Voter, Charles V. Banks, and Harvey Diehl
The compound, 1,2-cyclohexanedionedioxime, designated Nioxime, is similar to dimethyl-
glyoxime in yielding scarlet and yellow precipitates with nickel and palladium, which can be used for
the gravimetric determination of these metals. It is soluble in water, in contrast to dimethylglyoxime,
so that its use is theoretically unaccompanied by danger of contaminating the precipitates with excess
reagent or of solubility loss by the addition of alcohol. On the other hand, nioxime is a more power-
ful reducing agent than dimethylglyoxime, which introduces some complications in its use.
iiii II. '
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One part of nickel in ten million may be detected with the reagent.
The precipitation of nickel
nioxime is complete at pH values of three ard greater, and the precipitation may be made from a
solution of various anions, chloride, sulfate, perchlorate, nitrate, acetate, tartrate, and sulfo-
salicylate. The precipitation effectively separates nickel from a variety of metals including zinc,
beryllium, uranium, aluminum, the alkali and alkaline earth metals, manganese, cadmium, antimony,
and arsenic. Attempts to separate nickel from iron failed, as no suitable completing agent for the
latter was found which would prevent the precipitation of the iron and not interfere in the determi-
nation of the nickel.
The unique and useful applications of the 1,2-dioximes to analytical chemistry were extensively
reviewed in 1940.1 That 1,2-cyclohexanedionedioxime yielded a scarlet precipitate with nickel and
in fact was a very sensitive qualitative test for nickel was early discovered by Wallach. Feigl2
pointed out that 1,2-cyclohexanedionedioxime should be the ideal reagent for nickel, inasmuch as
its solubility in water would be a significant advantage over dimethylglyoxime, which must be made
up in alcohol or acetone. Although this attracted the attention of various analytical chemists, the
great difficulty in synthesizing 1,2-cyclohexanedionedioxime precluded a detailed study of its prop-
erties and uses as an analytical reagent; indeed, numerous, unreported attempts to prepare the rea-
gent met with signal failure, and it was only in 1945 that Rauh, Smith, Banks, and Diehl7 succeeded
in obtaining sufficient of the material to make possible its investigation. One of their methods of
preparation was later greatly improved by Hach,4 so that the compound is now available at moderate
price.* A command name, Nioxime, has been proposed for the reagent.
The uses of nioxime in the analytical chemistry of nickel and palladium were investigated as
part of the thesis for the MS degree by Banks. This work and also some by Voter, both interrupted
for war service, have now been continued and form the subject matter of this paper. In the meantime
work was done at Purdue University by Nellon and Griffing3 on the use of the reagent in the colori-
metric determination of nickel and iron. Publication of this work was unfortunately obstructed and
during the ensuing delay a short paper by certain English workers,5 dealing with the gravimetric
and colorimetric uses of nioxime, has appeared.
Ach Chemical and Oxygen Company, Ames, Iowa.
MDDC- 985 [ 1
is a white, crystalline material, melting at 189 to 1900, which, when properly prepared,
is free from any pink coloration due to contamination by iron, and which remains white indefinitely.
Its molecular weight
The solubility of nioxime in water
was determined by precipitatinga measured volume of a sat-
urated solution with an
of nickel: 0.82 g per 100 ml water at 21.50.
A 0.8 per cent aqueous solution of nioxime was used.
This solution keeps indefinitely.
A standard nickel solution was prepared from Mond nickel obtained from the International Nickel
Company. This nickel was analyzed spectrographically and found to be free from iron and cobalt. A
weighed amount of this nickel was dissolved in aqua regia and the solution evaporated to dryness five
times with concentrated hydrochloric acid to eliminate nitrate ions. By weighing the diluted nickel
chloride solution, the weight of nickel per weight of solution was found. This nickel concentration was
checked by an electrolytic determination of the nickel, the sample being measured by a weight buret.
The residual liquid was tested with nioxime to insure the complete deposition of the nickel. The
nickel content of the solution, as determined by the two methods, agreed well. (See Table 1.) The
value obtained by electrolysis
A 20 per cent solution of ammonium acetate
was prepared from reagent-grade salt and filtered.
Table 1. Standardization of nickel solution.
Weighing nickel and solution
g Ni/g solution
g Ni/g solution
Ten nickel solutions were made up in 100-ml volumetric flasks, with concentrations ranging
from one to ten parts in ten million.
To each solution were added three drops of 0.8 per cent nioxime
solution, followed by vigorous shaking. Observations made less than two minutes after the addition
of the reagent showed that each solution exhibited a color ranging from red for the more concen-
treated to pink for the one part in ten million. At the end of one hour, a red precipitate
in each flask.
The pH of the solutions as determined with
a glass electrode
A comparative test was performed using dimethylglyoxime (1 per cent in ethanol) on solutions
of like concentrations at a pH of 8. No visible coloration was detected until thirty minutes after
addition of the reagent and then only in those solutions of higher concentration. The sensitivity
of the nioxime for nickel determined this way
is greater than that reported by Wallach9 and the
English workers, swho reported one part in two million and one part in five million, respectively.
GRAVIMETRIC DETERMINATION OF NICKEL
Since hydrogen ions are liberated on the formation of the nickel derivatives of the 1,2-dioximes,
it is necessary to buffer the solution or otherwise control the pH by the addition of ammonia. Whereas
nickel dimethylglyoxime is generally precipitated from a mildly ammoniacal medium, it was found
best to precipitate nickel nioxime- from a slightly acid solution. This is an advantage, because it
.makes possible the separation of nickel from certain metallic ions without the use of completing
agents. Quantitative precipitation of nickel was obtained at a pH of 3 or higher.
SThe rate of precipitation and the pH of the solution determine the ease of filtration of the nickel
nioxime precipitate. If the nickel was precipitated by the dropwise addition of the nioxime solution
fto the buffered nickel solution, the precipitate formed clogged the filtering crucible and filtration
Swas quite difficult. If the pH of the solution was slowly raised from a point where the nickel nioxime
would not precipitate to a pH of about 4.5, the precipitate was filtered without trouble. This slow
precipitation was effected by the dropwise addition of a 20 per cent solution of ammonium acetate
with constant stirring. Precipitates formed at pH values above 7 were somewhat gelatinous, were
exceedingly difficult to filter, and exhibited a bluish coloration. The best results with respect to
accuracy and precision were obtained when precipitation was made from a slightly acid solution.
Nickel nioxime is formed by the union of one nickel atom with two molecules of nioxime with the
: liberation of two hydrogen ions, and the nickel derivative, Ni(C6H902N)2, molecular weight 340.99,
should contain 17.21 per cent nickel. The results of nearly a hundred determinations indicate,
however, that the nickel content is slightly lower than the theoretical. It has been shown that this
departure is independent of the anion present in the solution, of any foreign cations present, and in
general of any diverse ions present in the solution. The various reagents and distilled water were
ecked as possible sources of contamination and found to be without fault. A determination made on
the nickel chloride in water without the addition of acetate gave the same results. The data all indi-
cated that the positive error was caused by the coprecipitation of the reagent.
Results from a series of determinations in which the per cent excess of the nioxime was varied
showed that the error was nearly a linear function of the concentration of the excess nioxime for a
given weight of nickel (Figure 1).
0.1 0.2 0.3 0.4
qj MDDC 985
Since the volume of the solution was constant in these determinations, the per cent excess was
proportional to the nioxime concentration and thus determined the amount of nioxime coprecipitated
by the nickel nioxime precipitate. Washing the nickel nioxime precipitate with 95 per cent ethanol,
in which nioxime is fairly soluble and the precipitate insoluble, did not free the precipitate of the
reagent; nor did precipitation from 10 per cent alcohol solution change the result.
Since the magnitude of this error was a linear function of the
nioxime, an empirical
equation was easily developed by which the correct results for nickel could be calculated from the
weight of the precipitate and the total reagent added. The weight of nioxime used is the weight of
the nickel precipitate multiplied by the factor 0.834. The volume of 0.8 per cent solution used is then
0834 (Wt 'Ni nioxime ppt)
Vol used= -..........
with the volume added known, the per cent
Correction in g of Ni =
- --F__ _--r -,y
= 104 (Wt Ni nioxime ppt)
reagent is calculated. The correction is calcu-
nioxime) (Wt Ni nioxime ppt) (0.1721).
The result of the analysis is then calculated in the usual way
(Wt Ni nioxime) (0.1721)-(Corr in g Ni) x 00.
= Wt sample
The factor 5000 results from the observation that each 20 per cent excess nioxime caused a positive
error of one part in 250.
As the correction
is quite small, the per cent
of nioxime need only
be approximately known, and it
in a graduated cylinder.
is sufficient merely to measure the volume of nioxime solution added
Determinations conducted on a series of samples of different
size indicated that amounts of
5 to 25 mg could be successfully determined. The correction for the reagent carried
down need only be applied for amounts of nickel above 15 mg. The precipitation of small amounts
of nickel, less than 2 or 3 mg,
is slow. In determination 1 of Table
2 the solution
after two hours through the filter crucible containing the first precipitate.
Determination of various amounts of nickel.
Nickel Weight of Nickel
Determination taken precipitate. found Error
(gram) (gram) (gram) (milligram)
The nickel nioxime precipitate
was dried at various temperatures from 1000 to 1550. No further
loss in weight occurred at the higher temperatures. At temperatures above 1550, however, the pre-
cipitate turned brown and lost weight rapidly. The precipitate could not be ignited to the oxide for
as sublimation occurred before the decomposition could be effected.
Adjust the.volume of the solution containing about 25 mg of nickel to approximately 250 ml.
If a completing agent is needed to prevent the precipitation of other metals, it should be added before
continuing with the procedure. Add 8 ml of a solution of 0.8 per cent nioxime for each 10 mg of nickel
present, measuring with a graduated cylinder the volume of reagent added. Slowly add with stirring
enough concentrated hydrochloric acid to cause any red precipitate of nickel nioxime to dissolve.
Then add ammonia dropwise until a faint red coloration persists. Heat the solution to about 60.
From a buret add dropwise and with constant stirring 25 ml of the 20 per cent ammonium acetate.
Digest the solution with occasional stirring for 30 to 40 minutes at 60. Filter through a weighed
filter crucible of medium porosity, and wash with five portions of hot water. Dry at 110 for one
hour and weigh. Calculate the results as previously described. The pH of the solution just before
filtration will be between 4 and 5, if the procedure is carefully followed.
Table 3. Effect of various anions upon the determination of nickel.
Anion Anion Nickel taken precipitate Nickel found Error
present (grams) (gram) (gram) (gram) (mg)
*Small amount of chloride present
The effect of various anions upon the determination of nickel was studied. The weighed nickel
chloride solution was evaporated with sulfuric acid, nitric acid, or perchloric acid to eliminate the
chloride. The nickel nioxime was precipitated by the addition of the nioxime reagent to the acid
solution and neutralized with a 20 per cent solution of ammonium acetate. As shown in Table 3,
satisfactory results are obtained from chloride, nitrate, sulfate, and perchlorate solutions. Further
determinations in which tartrate, acetate, and sulfosalicylate were added
as the ammonium salts
to the nickel chloride solution showed that these anions do not affect the determination.
The determination of nickel in the presence of beryllium was studied. The separation was
effected both with and without sulfosalicylic acid
as a completing agent for the beryllium ion. As
beryllium hydroxide does not precipitate below a pH of 5.7,10 the completing agent is not necessary
when the determination
is conducted in the manner suggested. Table 4 summarizes the data obtained.
The precipitate from determination "three" was decomposed with nitric acid and ignited to the oxide.
Spectrographic analysis revealed the presence of less than 100 ppm beryllium, indicating a
Table 4. Determination of nickel in the presence of beryllium.
Beryllium Nickel Weight of Nickel
Determination present taken precipitate found Error
(gram) (gram) (gram) (gram) (mg)
1"* 0.2 0.0212 0.1243 0.0212 0.0
2* 0.2 0.0210 0.1232 0.0211 0.1
3 0.1 0.0242 0.1409 0.0241 0.1
4 0.2 0.0252 0.1482 0.0253 0.1
5 0.2 0.0270 0.1578 0.0270 0.0
6 0.3 0.0233 0.1363 0.0233 0.0
7 0.3 0.0241 0.1390 0.0238 0.3
* Contained 6
.5 grams of
Table 5 shows results that were obtained in separating nickel from various amounts of zinc.
There was no evidence of coprecipitation of zinc hydroxide with the nickel nioxime.
5. Determination of nickel in the presence of zinc.
Zinc Nickel Weight of Nickel
Determination present taken precipitate found Error
(gram) (gram) (gram) (gram) (mg)
1 1.0 0.0252 0.1474 0.0252 0.0
2 0.8 0.0234 0.1371 0.0234 0.0
3 0.5 0.0272 0.1595 0.0272 0.0
4 0.3 0.0239 0.1401 0.0239 0.0
5 0.1 0.0210 0.1226 0.0210 0.0
was determined in the presence
of uranyl, manganous, sodium, potassium, lithium,
barium, calcium, strontium, magnesium, cadmium, and arsenite ions.
ions are present with the nickel, tartrate must be added
When aluminum and antimonite
as a completing agent to prevent copre-
cipitation of aluminum hydroxide and antimonous hydroxide with the nickel nioxime. The data from
these separations are also shown in Table 6.
Table 6. Determination of nickel in the presence of various cations.
SNickel Weight of Nickel
Cation Cation taken precipitate found Error
present (gram) (gram) (gram) (gram) (mg)
Uranyl 0.55 0.0236 0.1385 0.0237 +0.1
Uranyl 0.23 0.0234 0.1368 0.0234 0.0
Manganous 0.50 0.0236 0.1381 0.0236 0.0
Manganous 0.10 0.0231 0.1351 0.0231 0.0
Potassium 0.10 each 0.0235 0.1375 0.0235 0.0
Calcium 3 0.10 each 0.0255 0.1491 0.0255 0.0
Magnesium 0.20 each 0.0220 0.1291 0.0221 +0.1
Antimonite* 0.14 0.0221 0.1301 0.0222 +0.1
Aluminum 0.20 0.0233 0.1362 0.0233 0.0
Arsenite 0.34 0.0234 0.1373 0.0235 +0.1
*Complexed with 0.2 gram of tartrate.
tComplexed with 1.2 grams of tartrate.
A method for the satisfactory quantitative separation of nickel from iron was not found. The
difficulty lay in finding a completing agent for the ferric iron. The possibility of using tartrate and
citrate was exhaustively investigated. However, these anions are known to reduce iron to the ferrous
state,8 which forms a very stable complex with nioxime, and incomplete precipitation of the nickel
results. Nioxime will also reduce ferric to ferrous iron. Ferric sulfosalicylate complex inhibits
the precipitation of the nickel nioxime, and postprecipitation occurs
as twenty four hours
Fluoride, phosphate, and pyrophosphate precipitate ferric iron, whereas dextrose, glycerine,
salicylate, d-mannitol and thiocyanate do not prevent hydrous ferric oxide from precipitating under
the conditions of the recommended procedure. Ferrocyanide was ruled out, since nickel ferrocyanide
-Bipyridine complexes nickel
as well as ferrous iron,6 and nickel nioxime
precipitated in its presence.
1. Diehl, H.
"The Application of the Dioximes to Analytical Chemistry,"
G. Frederick Smith
Chemical Company, Columbus, Ohio, 1940.
2. Feigl, F.,
"Qualitative Analyse mit Hilfe von Tipfelreaktionen,
p 73, Akademische Verlags-
gesellschaft M.B.H., Leipsig, 1931.
3. Griffing, M., Ph.D. Thesis,
Purdue University, Lafayette, Ind. 1944.
4. Hach, C. C., C.
5. Johnson, W. C.,
6. Moss, M. L., w
, and H. Diehl, unpublished work.
and M. Simmons, Analyst 71:554
ith M. G. Mellon, Ind. Eng. Chem., Anal. Ed.,
7. Rauh, E. G.,
G. F. Smith, C. V. Banks,
and H. Diehl, 2. Org. Chem. 14:862
8. Schoras, J., Ber. 3:11 (18
9. Wallach, O., Ann. 437:175
10. Willard, H. H. and H. Diehl,
New York, 1943.
"Advanced Quantitative Analysis.
p 45, D. Van Nostrand Co.,
UNIVERSITY OF FLORIDA
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