Millipore Spectroquant Multy Operating Manual page 220

Standard solution of sulfite
Preparation of a stock solution:
Dissolve 1.57 g of sodium sulfite and 0.4 g of Titriplex
with distilled water in a calibrated or conformity-checked
1000-ml volu metric flask and make up to the mark with
distilled water.
The standard solution prepared according to this procedure has
a concentration of approx. 1000 mg/l sulfite.
Precise assay of the stock solution:
Place 50.0 ml (full pipette) of the sulfite stock solution and
5.0 ml (full pipette) of hydrochloric acid 25 % in a 300-ml
conical flask.
To this solution add 25.0 ml (full pipette) of iodine solu tion
0.05 mol/l and process immediately. After mixing the contents
of the flask, sub sequently titrate with sodium thiosulfate so-
lution 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
from blue to colorless.
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 sulfite = (C2 – C1) x 80.06
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 and buffer solution pH 9.00.
This is done in the following manner:
Withdraw the desired aliquot from the stock solution, place in
a calibrated or conformity-approved 1000-ml volumetric flask,
add 20 ml of buffer solution pH 9.00, make up to the mark
with distilled water, and mix.
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:
1.06657.0500 Sodium sulfite anhy-
III GR
®
1.08418.0100 Titriplex
1.09099.1000 Iodine solution
1.09147.1000 Sodium thiosulfate
1.00316.1000 Hydrochloric acid
1.05445.0500 Zinc iodide-starch
1.09461.1000 Buffer solution
1.16754.9010 Water for analysis
Chapter 5.2 | Page 20 of 23
drous for analysis
EMSURE®
III GR for
®
analysis
0.05 mol/l Titripur®
solution 0.1 mol/l
Titripur®
25 % for analysis
EMSURE®
solution GR for
analysis
pH 9.00 Certipur
®
EMSURE®