Processing kodak motion picture films, module 3 analytical procedures

Iodometric Determination of Sodium Metabisulfite in Accelerator Solution
ECN-2-1340
ECR-1340A
Process ECN-2 ECP-2D VNF-1/LC RVNP
Formulas AB-2 — AB-3 AB-3
PRINCIPLE
The 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 sodium metabisulfite (Na2S2O5 ) and the KODAK
Bleach Accelerator PBA-1, in the sample. The unreduced
part is measured by titration against standard sodium
thiosulfate with starch as the indicator. Since the quantity of
sodium thiosulfate used in the titration is equivalent to the
quantity of unreduced iodine, the concentration of sodium
metabisulfite is calculated from the difference between the
total iodine and the quantity of sodium thiosulfate used in the
titration. A stoichiometric factor in the calculation corrects
for the KODAK Persulfate Bleach Accelerator PBA-1,
contribution in the titration. KODAK Persulfate Bleach
Accelerator PBA-1 must be analyzed prior to the analysis of
sodium metabisulfite (see Method 2100B, Potentiometric
Determination of Kodak Persulfate Bleach Accelerator
PBA-1 in Accelerator Solution).
The method is accurate in that it measures the amount of
sodium metabisulfite existing in the mix. In some mixes
containing a relatively small amount of sodium
metabisulfite, an appreciable portion of the sodium
metabisulfite is oxidized during mixing, producing results
lower than mix level.
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).
REAGENTS
Use reagents that are ACS Reagent Grade unless specified
otherwise.
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
PROCEDURE
Sample Treatment
1. Pipet (wipe the Pipet before leveling) 50.0 mL of
standardized 0.1 N potassium iodate into a 250-mL
conical flask.
2. Add 25 mL of 7.0 N sulfuric acid from a tip-up pipet.
3. Add 25 mL of 0.60 M potassium iodide from a tip-up
pipet.
4. Pipet (wipe) 10.0 mL of sample into the flask.
Titration
1. Titrate with standardized 0.1 N sodium thiosulfate to a
yellow color.
2. Add approximately 5 mL of starch indicator and
continue the titration until the blue color disappears.
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03 1