Release 06/2014
Spectroquant
®
photometers NOVA 60 and Pharo photometers
Instructions for the Preparation of Standard Solutions
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
water.
The stock solution pre pared according to this procedure has a concen-
tration 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 sulfuric 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 minute, sub sequently titrate with sodium thio-
sulfate 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 0.1 mol/l (ml)
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 procedure 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 thio-
sulfate 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
®
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