Processing kodak motion picture films, module 3 analytical procedures

PROCEDURE
A. Spectrophotometer Zeroing
1. Adjust the spectrophotometer wavelength to 477 nm.
2. Zero the spectrophotometer versus air.
B. Blank Determination
1. Add 25 mL of 2.5 N sulfuric acid, 10 mL of 40 g/L
potassium persulfate, and 25 mL of 200 g/L
ammonium thiocyanate to a 100-mL volumetric flask.
2. Swirl to mix the reagents and dilute to the mark with
reagent water. Invert the flask 6 to 10 times to mix.
3. Rinse a clean 1-cm silica cell 3 to 5 times with blank
solution from Step 2 and fill the silica cell with the
blank solution. Rinse the outer surfaces of the cell with
reagent water and wipe dry with a tissue. Place the cell
into the spectrophotometer sample cell holder.
4. Record absorbance of blank at 477 nm as Ablk .
C. Sample Treatment
1. Add approximately 200 mL of reagent water to a
250-mL volumetric flask.
2. Pipet 5.00 mL of the sample into the 250-mL flask. Fill
to volume with reagent water. Invert flask 6 to 10
times to mix.
3. Add 25 mL of 2.5 N sulfuric acid and 10 mL of
40 g/L potassium persulfate to a 100 mL volumetric
flask. Swirl to mix.
4. Pipet 3.00 mL of diluted sample from Step 2, into a
l00-mL volumetric flask.
5. Add 25 mL of 200 g/L ammonium thiocyanate to the
l00-mL volumetric flask while swirling the flask. Fill
to volume with reagent water. Invert the flask 6 to 10
times to mix.
6. Rinse the 1-cm silica cell 3 to 5 times with sample
from Step 5, and then fill the silica cell with the
sample. Rinse the outer surfaces of the cell with
reagent water and wipe dry with a tissue. Place the cell
into the spectrophotometer sample cell holder.
7. Record absorbance of sample at 477 nm as Aspl. Note: If using a single-beam spectrophotometer (as opposed
to a double-beam spectrophotometer) the procedure is the
same.
Calculations
∆A 477 = A spl – A blk
g/L Fe =
Where:
(∆A 477 )(DF)
(Absorptivity)
DF = Dilution
factor
Note: Use APPENDIX 1 to determine the absorptivity of the
iron-thiocyanate complex. Each spectrophotometer may
yield a different absorptivity value.
Example Calculation:
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03 3
=
=
(250 mL)(100 mL) =1666
(5.00 mL)(3.00 mL)
250 mL = volume of first dilution
5.00 mL = volume of sample pipeted into first
volumetric flask
100 mL = volume of second dilution
3.00 mL = volume of first dilution pipeted into second
volumetric flask
Absorptivity = 196 L/g-cm)
∆A 477 = A spl – A blk
∆A 477 = 0.479 – 0.043 = 0.436
g/L Fe =
(∆A 477)(DF)
(Absorptivity)
=
(0.436)(1666) =3.7
(196)