LaMotte DC1600 Colorimeter - Manual (Page 17)

CHLORINE - BROMINE - IODINE
DPD METHOD CODE 3643
QUANTITY CONTENTS CODE
2 x 100 *DPD #1 Instrument Grade Tablets *6903-J
100 DPD #3 Instrument Grade Tablets 6197-J
15 mL Glycine Solution 6811-E
1 Tablet Crusher 0175
*WARNING: Reagents marked with a * are considered hazardous substances. Material Safety Data Sheets (MSDS) are supplied for
these reagents. For your safety, read label and accompanying MSDS before using.
NOTE: To distinguish bromine, free chlorine, total chlorine and combined chlorine, order Glycine Solution (Code
6811-E).
CHLORINE
All water for cities and communities must be disinfected; even waters that come from clean sources, protected watersheds,
reservoirs, and deep wells, are commonly disinfected to assure safety. Chlorine is the most commonly used disinfectant for
several reasons: it is effective against a wide range of microorganisms, its cost is low, and the methods of applying it have
been well developed. If chlorine is present in the water for a few minutes, disease producing bacteria will be destroyed. A
number of conditions affect the disinfecting action of chlorine. In municipal systems these can be controlled so that if
chlorine is detectable, it can be assumed that bacteria have been killed. The factors that influence the rate of disinfection
are temperature, pH, presence of other materials that react with chlorine, time, and the concentrations of the various
chlorine combinations that are formed in the water with ammonia and other substances that react with chlorine.
The fact that chlorine can be easily detected and measured makes chlorine a favorite water disinfectant of those concerned
with the public safety of water supplies. Chlorine concentrations in the range of 0.1 to 0.4 milligrams per liter are usually
maintained in municipal supplies.
Chlorine can be added in the form of chlorine gas, liquid sodium hypochlorite (bleach), granular calcium hypochlorite or
as organic chlorine compounds. Chlorine is not present in natural water supplies; if it is present it is the result of
chlorination of a water supply or of chlorinated compounds being discharged as waste from industrial operations. The
presence of chlorine in concentrations above 0.5 parts per million should be considered evidence of pollution from chlorine
treated effluents or from a process in which high concentrations of chlorine are used.
APPLICATION: Drinking, surface, saline waters; swimming pool water; domestic and industrial wastes.
RANGE: 0.00 – 4.0 ppm Chlorine
METHOD: In the absence of iodide, free available chlorine reacts instantly with DPD to produce a red
color. Subsequent addition of potassium iodide evokes a rapid color response from the
combined forms of chlorine (chloramines).
SAMPLE HANDLING
& PRESERVATION: Chlorine in aqueous solutions is not stable, and the chlorine content of samples or solutions,
particularly weak solutions, will rapidly decrease. Exposure to sunlight or agitation will
accelerate the reduction of chlorine present in such solutions. For best results, start analysis
immediately after sampling. Samples to be analyzed for chlorine cannot be preserved or stored.
INTERFERENCE: The only interfering substance likely to be encountered in water is oxidized manganese. The
extent of this interference can be determined by treating a sample with sodium arsenite to
destroy the chlorine present so that the degree of interference can be measured.
Iodine and bromine can give a positive interference, but these are not normally present unless
they have been added as disinfectants.
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