Processing kodak motion picture films, module 3 analytical procedures

Procedure
Preparation of 10 g/L Iron Stock Solution.
1. Measure 200 mL of concentrated nitric acid into a
250-mL graduated cylinder. Slowly pour the acid into
a 1-L beaker containing 300 mL of reagent water and
a magnetic stir bar. Mix thoroughly.
2. Weigh 2.50 g of iron wire and record the weight to the
nearest 0.1 mg. Wear white cotton gloves to keep
finger oils and moisture from the wire. Use complete
packs of wire to avoid contamination from wire cutting
devices. Two or three of the 0.75-g packs will contain
a weight close to the stated amount (each typically
contains more than the nominal 0.75 g).
3. Place the iron wire into a 1-L beaker with a magnetic
stirring bar. Place the beaker on a warm, hot-plate/
stirrer.
4. Slowly add about 125 mL of the diluted nitric acid
(prepared in step 1) to the iron wire in the beaker. The
iron wire will begin to dissolve and the acid will begin
to boil.
5. Once the wire has totally dissolved, immediately allow
the solution to cool to room temperature.
Quantitatively transfer the cooled solution into a
250-mL volumetric flask.
6. Fill the volumetric flask to the mark with reagent
water. Invert the flask 6–10 times to mix.
Note: This solution is stable for six months and should be
stored in either plastic or colorless glass bottles (do not store
in brown glass bottles as extraneous iron will be extracted
from the glass).
Calculations
Conc. of 10 g/L stock
standard solution
Where:
= weight from step 2 x 0.9999 x 4
250 x 4
0.9999 = assay value of iron wire supplied by Aldrich
4 = factor to convert 250 mL to 1 L
250 = volume of stock solution (mL)
Absorptivity of Iron-Thiocyanate Complex
1. Zero the spectrophotometer as described in the Zero
the Spectrophotometer Procedure of the above
method. Prepare and record the absorbance of a
reagent blank described in the Blank Procedure of the
above method (ABSblk ).
2. Pipette 3.0 mL of the 10 g/L iron stock solution into a
1-L volumetric flask containing 500 mL of 0.5 N
nitric acid. Dilute to volume with 0.5 N nitric acid,
stopper, and invert several times (6-10) to mix.
This is the absorptivity stock solution (approximately
30 mg/L Fe).
3. To a 100-mL volumetric flask, add 10 mL of 5 N nitric
acid and 1 mL 40 g/L potassium persulfate. Swirl to
mix.
4. Pipette 3.0 mL of the stock solution from step 2, into
the flask in step 3, with swirling.
5. Add 25 mL of 200 g/L ammonium thiocyanate to the
flask (step 4) with swirling. Dilute to volume with
reagent water. Stopper and invert 6–10 times to mix.
This is Std 1.
6. Rinse the 1-cm silica spectrophotometer cell several
times with the sample. Fill the cell and rinse the outer
surfaces with reagent water. Wipe dry with a soft
tissue and place the cell into the sample beam cell
holder of the spectrophotometer.
7. Record the absorbance of Std 1 at 477 nm as ABSstd 1 .
Absorbance should be recorded within 2 minutes of
sample preparation.
8. Repeat steps 3 to 7, two more times.
9. Repeat steps 2 to 8, substituting the following pipette
sizes into step 4 (see the following table). Record
absorbances with the corresponding Std #.
Pipette Size (mL) Std #
5.0 Std 2
10.0 Std 3
15.0 Std 4
10. The linear nature of the relationship between
absorbance at 477 nm and iron concentration is shown
in the Typical Absorptivity Table with the
accompanying Figure, Calibration of Total Iron in
ECN-2 or ECP-2 “KUL” Bleach.
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03 5