LaMotte COD3 Plus, Operator'S Manual

Page: 106 / 119

APPLICATION: Drinking, surface and saline waters; domestic and industrial
wastes.
RANGE: 0.00–1.50 ppm Sulfi de
MDL: 0.06 ppm
METHOD: Under suitable conditions the sulfi de ion reacts with
p-aminodimethylaniline and ferric chloride to produce
methylene blue in proportion to the sulfi de concentration.
Ammonium phosphate is added to remove the color due to
the ferric iron.
SAMPLE HANDLING &
PRESERVATION: Samples must be taken with a minimum of aeration since
sulfi de is volatilized by aeration and any oxygen which is
taken up will destroy sulfi des by chemical action. Samples
that are used for total sulfi de concentrations may be
preserved by adding 2M zinc acetate solution at a dosage
of 2 mL per liter of sample. This precipitates sulfi de as inert
zinc sulfi de. Determination of dissolved sulfi des in samples
not preserved with zinc acetate must be started within 3
minutes of sampling.
INTERFERENCES: Strong reducing agents such as sulfi te, thiosulfate, and
hydrosulfi te prevent the formation of the color or diminish
its intensity. High concentrations of sulfi de will inhibit
the reaction, but dilution of the sample prior to analysis
eliminates this problem.
Testing
Sulfi de
, Low Range COD3 Plus Colorimeter 10.16