Millipore Spectroquant Multy Operating Manual page 219

Standard solution of sulfide
Preparation of a stock solution:
Dissolve 5.0 g of glass-clear, if necessary washed crystals of
sodium sulfide hydrate GR with distilled water in a calibrated
or conformity-checked 1000-ml volumetric flask and make up
to the mark with distilled.
The stock solution pre pared according to this procedure has a
concentration of approx. 1000 mg/l sulfide.
Precise assay of the stock solution:
Place 100 ml of distilled water and 5.0 ml (full pipette) of sul-
furic acid 25 % in a 500-ml ground-glass-stoppered conical
flask. To this solution add 25.0 ml (full pipette) of the sulfide
stock solution and 25.0 ml (full pipette) of iodine solu tion
0.05 mol/l. Shake the contents of the flask thoroughly for about
1 min, sub sequently titrate with sodium thiosulfate solution
0.1 mol/l until the yellow iodine color has disappear ed, add 1 ml
of zinc iodide-starch solution, and con tinue to titrate until a
milky, pure white color emerges.
Calculation and preparation of the standard solution:
C1 = consumption of sodium thiosulfate solution 0.1 mol/l
C2 = quantity of iodine solution 0.05 mol/l (25.0 ml)
mg/l sulfide = (C2 – C1) x 64.13
Further investigational concentrations may be prepared from
the stock solution exactly deter mined according to the pro-
cedure described above by diluting accordingly with distilled
water.
Stability:
When stored in a cool place (refrigerator), the stock solution
of approx. 1000 mg/l remains stable for at most one day. The
diluted standard solutions (investigational concentrations) must
be used immediately.
Reagents required:
Sodium sulfide
hydrate approx. 60 %
GR for analysis
1.09099.1000 Iodine solution
0.05 mol/l Titripur®
1.09147.1000 Sodium thiosulfate
solution 0.1 mol/l
Titripur®
1.00716.1000 Sulfuric acid 25 %
for analysis EMSURE®
1.05445.0500 Zinc iodide-starch
solution GR for
analysis
1.16754.9010 Water for analysis
EMSURE®
Chapter 5.2 | Page 19 of 23