Processing kodak motion picture films, module 3 analytical procedures

Titrimetric Determination of Persulfate in Persulfate Bleach
ECR-1125B
Process ECN-2 ECP-2D VNF-1/LC RVNP
Formulas — — SR-45 SR-45
INTRODUCTION
This method is based upon the oxidation of ferrous ion by
persulfate in an acid solution at room temperature. A known
excess of ferrous ion is added to the sample and the residual
ferrous ion is titrated with standardized sulfato cerate. A
blank determination should be run daily because ferrous
solutions are slowly oxidized by air during use.
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
The 95 percent confidence limits for an individual
determination are expected to be ± 0.24 g/L of total
oxidizing compounds reported as potassium persulfate.
REAGENTS
Use reagents that are ACS Reagent Grade unless specified
otherwise.
7.0 N Sulfuric Acid, H 2 SO 4
0.25 N Ferrous Ammonium Sulfate,
Fe(NH 4 ) 2 (SO 4 ) 2 6H 2 O
0.05 N Sulfato Cerate (standardized to 4 decimal places)
Ferroin Indicator
PROCEDURE
Persulfate Determination
1. Pipet (wipe the pipet before leveling) the indicated
sample size into a 250-mL conical flask equipped with
a magnetic stir bar.
Process Sample Size
VNF-1/LC 1.00 mL
RVNP 1.00 mL
2. Add 50 mL of distilled water from a tip-up pipet.
Warning
ACID. Avoid contact with skin and eyes. In case of
contact, flush with water.
3. Add 15 mL of 7.0 N sulfuric acid from a tip-up pipet.
4. Pipet 10.0 mL of 0.25 N ferrous ammonium sulfate
into the flask. Using a squeeze bottle, wash down the
sides of the flask with distilled water.
5. Swirl the solution to mix, stopper the flask and let it
stand for 3 minutes.
Note: Longer standing times do not adversely affect
the titration providing the solution is protected
from air.
6. Add 4 drops of Ferroin indicator and from a 50-mL
buret, titrate with standardized 0.05 N sulfato cerate to
the first light cyan color.
7. Record the end point as mL A.
Reagent Blank Determination
Note: A reagent blank should be run at least once per day
because the 0.25 N ferrous ammonium sulfate will slowly
change with usage.
1. Add 50 mL of distilled water, with a tip-up pipet, to a
250-mL conical flask equipped with a magnetic
stir bar.
2. Repeat Steps 3 through 6 of the Persulfate
Determination section.
3. Record the end point as mL B.
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03 1