LaMotte SMART3 Colorimeter - Manual (Page 280)

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.
SULFIDE, Low Range SMART3 Test Procedures 11.10
Test P
rocedures