415
Interferences
Soluble Sulfides
Determine soluble sulfides by centrifuging the sample in
completely filled, capped tubes and analyzing the supernatant.
Insoluble sulfides are then estimated by subtracting the soluble
sulfide concentration from the total sulfide result.
Summary of Method
Hydrogen sulfide and acid-soluble metal sulfides react with
N, N-dimethyl-p-phenylenediamine oxalate to form methylene
blue. The intensity of the blue color is proportional to the sulfide
concentration. High sulfide levels in oil field waters may be
determined after dilution.
Pollution Prevention and Waste Management
Sulfide 2 Reagent contains potassium dichromate. The final
solution will contain hexavalent chromium (D007) at a
concentration regulated as a hazardous waste by Federal RCRA.
See Section 3 for more information on proper disposal of these
materials.
Interfering
Substance
Interference Levels and Treatments
Strong reducing
substances (sulfite,
thiosulfate and
hydrosulfite)
Interfere by reducing the blue color or preventing
its development.
Sulfide, high levels High concentrations of sulfide may inhibit full color
development and require sample dilution. Some sulfide loss
may occur when the sample is diluted.
Turbidity For turbid samples, prepare a sulfide-free blank as follows. Use
it in place of the deionized water blank in the procedure.
1. Measure 25 mL of sample into a 50-mL erlenmeyer flask.
2. Add Bromine Water dropwise with constant swirling until a
permanent yellow color just appears.
3. Add Phenol Solution dropwise until the yellow color just
disappears. Use this solution in Step 4 in place of deionized
water.
SULFIDE, continued
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