Group Title: Lake Alfred AREC reseach report - University of Florida Agricultural Research and Education Center ; CS-79-1
Title: Using A D.P.D. (N,N. Diethyl-P-Phenylenediamine) test kit for measuring free available chlorine
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Permanent Link: http://ufdc.ufl.edu/UF00072471/00001
 Material Information
Title: Using A D.P.D. (N,N. Diethyl-P-Phenylenediamine) test kit for measuring free available chlorine
Series Title: Lake Alfred AREC reseach report
Physical Description: 1 leaf : ; 28 cm.
Language: English
Creator: Ford, Harry W., 1922-
Agricultural Research and Education Center (Lake Alfred, Fla.)
Publisher: University of Florida, IFAS, Agricultural Research and Education Center
Place of Publication: Lake Alfred FL
Publication Date: 1980
Edition: Rev. ed.
 Subjects
Subject: Irrigation -- Equipment and supplies -- Maintenance and repair -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: Harry W. Ford.
General Note: Caption title.
General Note: "5/14/79 (Revised 11/15/80)-HWF-100."
 Record Information
Bibliographic ID: UF00072471
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 76883475

Full Text




Lake Alfred AREC Research Report-CS79-1
5/14/79 (Revised 11/15/80)-HWF-100

USING A D.P.D. (N,N-DIETHYL-P-PHENYLENEDIAMINE) TEST KIT FOR MEASURING
FREE AVAILABLE CHLORINE

Harry W. Ford
University of Florida, IFAS
Agricultural Research and Education Center
Lake Alfred, Florida 33850

Liquid sodium hypochlorite (NaOCI), commonly called household
or swimming pool bleach, is the only bactericide that has a
24(c) approved EPA label for use in low volume irrigation systems
in Florida. Chlorine gas and HTH (calcium hypochlorite) do not
have a label.

The D.P.D. test kit is essential when using liquid chlorine as a bactericide and
algacide biocidee) in low volume irrigation systems. Chlorine, either as a gas (C12) or
as liquid sodium hypochlorite (NaOCI), is excellent but both must be carefully monitored.
Dumping excessive amounts of chlorine into an irrigation system can result in injury to
young trees. Inhibiting bacterial growths requires a minimum contact time of 30 minutes
(45 minutes of actual injection) and a miminum free available chlorine concentration of
0.5-1.0 ppm (mg/l) as measured at the end of the line or 2.0-3.0 ppm free chlorine near
the injection site. Free chlorine is excess chlorine in the system and not total chlorine
originally added.

Chlorine used as a biocide should not be confused with chloride that is common in
fertilizers and table salt. Chlorine is a very active and toxic agent at high
concentrations. When injected into irrigation lines, some of the'chlorine reacts with
metals such as iron and is destroyed. Hydrogen sulfide and sulfur dioxide also destroy
chlorine, while ammonia reacts and forms chloroamines. Chlorine also reacts with organic
matter and organic compounds although the change may be one of adsorption rather than a
complete chemical destruction of the active chlorine. Chlorine adsorbed on organic matter
does not kill organisms. The active agent that kills bacteria is the excess hypochlorous
acid molecule (HOC1) which is part of the free available chlorine. The exact reaction
with bacteria is not entirely clear but hypochlorous acid levels must be increased at pH
values above 7.5. Above pH 7.8, hydrochloric acid must be used to reduce the pH so that
hypochlorous acid will be effective.

Test Kits for Chlorine. The orthotolidine (yellow color)-type test kit, that is often
used for swimming pools, is unsatisfactory with low volume irrigation systems. The
swimming pool kits measure only total chlorine but not the free chlorine residual.

A good quality D.P.D. test kit will read both total chlorine and free chlorine.
Different chemicals are used for measuring each type of chlorine. The water turns pink if
chlorine is present. The color is matched against suitable standards--often a color wheel
calibrated to read in ppm (mg/l). Total chlorine readings are helpful when one is first
trying to detect chlorine in the irrigation system. Free chlorine is the value that
determines the biocidal action of the chlorine in the irrigation line. READ FOR FREE
CHLORINE WITHIN 15 SECONDS AFTER ADDING THE REAGENT.

D.P.D. test kits are extremely simple. Directions come with the kit. They should be
used frequently when chlorine is being injected. They will pay for themselves by savings
in chlorine and by indicating the right concentration of chlorine to kill bacteria. If
there is no free chlorine, even though chlorine has been injected into the system,
bacteria will continue to grow and the treatment will have been wasted.

The kits are available from chemical supply sources specializing in water problems and
also from some low volume irrigation supply sources in Florida. Some swimming pool
companies may be stocking the kits but very few have the total and free chlorine color
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