| Material Information
||Using A D.P.D. (N,N. Diethyl-P-Phenylenediamine) test kit for measuring free chlorine residual
||Lake Alfred AREC reseach report
||2 p. : ; 28 cm.
||Ford, Harry W., 1922-
Agricultural Research and Education Center (Lake Alfred, Fla.)
||University of Florida, IFAS, Agricultural Research and Education Center
||Place of Publication:
||Lake Alfred FL
||Irrigation -- Equipment and supplies -- Maintenance and repair -- Florida ( lcsh )
||government publication (state, provincial, terriorial, dependent) ( marcgt )
non-fiction ( marcgt )
||Statement of Responsibility:
||Harry W. Ford.
| Record Information
||University of Florida
||All rights reserved by the source institution and holding location.
||oclc - 76805123
1 3 Lake Alfred AREC Research Report-CS79-l
-/ USING A D.P.D. (N,N.DIETHYL-P-PHENYLENEDIAMINE) T T
KIT FOR MEASURING FREE CHLORINE RESIDUAL JN 12 1979
Harry W. Ford Ui of ori
University of Florida, IFAS Ui.of Forida
Agricultural Research and Education Center
Lake Alfred, Florida 33850
Liquid sodium hypochlorite (NaOCI) is the only biocide that has
an EPA approved 24(c) label for use in low pressure irrigation
systems in Florida.
The D.P.D. test kit is essential when using liquid chlorine as a
bactericide and algacide biocidee) in low pressure irrigation systems.
Chlorine, either as a gas (C12) or as liquid sodium hypochlorite (NaOCI),
is excellent but it must be monitored carefully and correctly. 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 (40 minutes of actual injection) and a minimum
free residual 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 residual 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. It 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 chloroamine, a weak biocide. Chlorine also reacts with organic
matter and organic compounds although the change is often 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 which is part of
the free chlorine residual. The exact reaction with bacteria is not entirely
clear but hypochlorous acid levels must be increased at pH levels above 7.5.
Above pH 8.0, hydrochloric acid must be used to reduce the pH so that
hypochlorous acid will be effective.
The orthotolidine (yellow color)-type test kit, that is often used
for swimming pools,is unsatisfactory with low pressure irrigation systems.
The swimming pool kits measure only total chlorine but not the free chlorine
A good quality D.P.D. test kit will read both total chlorine and free
chlorine residual. 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
Using a D.P.D. (N,N.Diethyl-P-Phenylenediamine)
Test Kit for Measuring Free Chlorine Residual
in ppm (mg/1). 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
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 residual, even though chlorine has been injected into
the system, bacteria will continue to grow and the treatment will have
The kits are available from chemical supply sources specializing
in water problems and also from some low pressure irrigation supply
sources in Florida. Some swimming pool companies may be stocking the
kits but very few have the total and free residual color wheel type.