Processing kodak motion picture films, module 3 analytical procedures

Iodometric Determination of Total Sulfite in Reversal Color Developers Containing KODAK
Reversal Agent, RA-1
ECR-1303
Process ECN-2 ECP-2D VNF-1/LC RVNP
Formulas — — DR-150/151 DR-150
INTRODUCTION
KODAK Reversal Agent, RA-1 contributes a positive
interference to the iodometric determination of the total
sulfite in a color developer. The effect of this interference
can be corrected if the concentration of RA-1 is known. The
iodometric titration and known reversal agent concentration
can then be used to calculate the real concentration of
sodium sulfite in the sample.
PRINCIPLE
For the iodometric titration, the developer sample is added to
an excess of iodine, formed by acidifying standard
potassium iodate solution and adding potassium iodide. Part
of the iodine is reduced to iodide by the sulfite in the sample;
the remaining iodine is measured by titrating it with standard
sodium thiosulfate using starch indicator. Since the quantity
of sulfite is equivalent to the quantity of reduced iodine and
since the quantity of sodium thiosulfate used in the titration
is equivalent to the quantity of remaining iodine, the
difference between the total iodine and the volume of
sodium thiosulfate is a measure of the sodium sulfite
concentration.
In developers containing RA-1, some iodine is also
reduced by the reversal agent and this will erroneously be
calculated as sulfite unless a correction is made. The RA-1 is
analyzed using Method ECR-0001-1 (or subsequent
revision).
This method requires handling potentially hazardous
chemicals. Consult the Material Safety Data Sheet for each
chemical before use. MSDS's are available from your
chemical supplier.
Note: Use pipets and volumetric glassware meeting the
“Class A” definition by the National Institute of Standards
and Technology (NIST).
RELIABILITY
Photographic-grade sodium sulfite (Na 2 SO 3 ) is usually less
than 100 percent pure (minimum assay is 98.5 percent).
Photographic-grade sodium bisulfite (NaHSO 3 ) is a mixture
of sodium bisulfite, sodium metabisulfite (Na 2 S 2 O 5 ), and
water. Its purity, as determined by an iodine titration and
expressed as sodium bisulfite, is approximately
107.5 percent. If it were pure sodium metabisulfite it would
assay 110 percent as sodium bisulfite. One gram of
photographic-grade sodium bisulfite is equivalent to
1.30 grams of sodium sulfite (100 percent).
Correction equations were calculated from ten analyses of
sodium sulfite in color developer with RA-1 concentrations
ranging from 0 to 125 mg/L. The 95 percent confidence
limits are essentially the same for developers with or without
RA-1. The 95 percent confidence limits for an individual
determination are ± 0.05 g/L sodium sulfite.
Reagents
Use ACS Reagent Grade reagents unless otherwise
specified.
0.1 N Potassium Iodate, KIO 3
(standardized to 4 decimal places)
7.0 N Sulfuric Acid, H 2 SO 4
0.60 M Potassium Iodide, KI
0.1 N Sodium Thiosulfate, Na 2 S 2 0 3
(standardized to 4 decimal places)
Starch Indicator
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03 1