Processing kodak motion picture films, module 3 analytical procedures

Potentiometric Determination of Silver in Fixing Baths
1208E
Process ECN-2 ECP-2D VNF-1/LC RVNP
Formulas — — F-36 F-38
INTRODUCTION
The sample is made alkaline to prevent the decomposition of
sodium thiosulfate, which occurs in acid solutions.
Ethylenedinitrilo tetraacetic acid (EDTA) is added to
minimize interference of other metal ions. The EDTA
reagent does not prevent interference from zinc ions. Gelatin
is added to prevent the coagulation of the silver sulfide that
is formed. This prevents the coagulated silver sulfide from
occluding the silver ions.
The sample containing silver is titrated potentiometrically
with standardized sodium sulfide using a silver billet/double
junction electrode pair. Changes in the volume of sample and
of sodium hydroxide/EDTA reagent affect the silver results.
If a small amount of sample is used, the sample volume must
be adjusted to about 300 mL with 1.0 M sodium thiosulfate.
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.
RELIABILITY
Four fixing baths containing 0.100 to 1.00 g/L silver (Ag)
were analyzed by two analysts. The 95 percent confidence
limits for an individual determination are ± 0.01 g/L silver.
SPECIAL APPARATUS
pH Meter or Automatic Titrator
Reference Electrode, Double Junction, Orion No. 900200
or equivalent (filled with 10 percent potassium nitrate
bridge solution in outer chamber)
Indicator Electrode, Silver Billet, Beckman No. 39261 or
equivalent
Note: Use pipets and volumetric glassware meeting the
“Class A” definition by the National Institute of Standards
and Technology (NIST).
REAGENTS
Use ACS Reagent Grade reagents unless specified
otherwise.
1.0 M Sodium Thiosulfate, Na 2 S 2 O 3
1 N Sodium Hydroxide/Ethylenedinitrilo Tetraacetic Acid
(EDTA) Reagent, 1 N NaOH/EDTA
4 g/L Gelatin
0.06 N Sodium Sulfide, Na 2 S
(standardized to 4 decimal places)
PROCEDURE
Sample Treatment
1. Pipet (wipe the pipet before leveling) sample into a
600-mL beaker according to the table below.
2. From a 250-mL graduated cylinder, add to the 600-mL
beaker the amount of 1.0 M sodium thiosulfate
indicated in the table.
Silver
Concentration
g/L
Sample,
mL
Less than 1 300 *
1.0 M Sodium
Thiosulfate,
mL
1 to 3 100.0 200
More than 3 50.0 250
* Use a graduated cylinder.
3. Add 100 mL of 1 N NaOH/EDTA reagent from a
50-mL tip-up pipet.
4. Add 10 mL of 4 g/L gelatin from a tip-up pipet.
Titration
Titrate the sample with standardized 0.06 N sodium sulfide
using a silver billet/double junction electrode pair. For
instructions, see Method ULM-0003-01, Potentiometric
Titrations for Photoprocessing Solutions, (or subsequent
revision).
Note: Avoid unnecessary exposure of the standardized
sodium sulfide to air. The reagent should be standardized
each week. Discard all unused reagent remaining in any open
bottles at the end of each day (60 mL reagent bottles are
suggested for storage of 0.06 N sodium sulfide).
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03 1
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