Processing kodak motion picture films, module 3 analytical procedures

Absorptivity of Iron-Thiocyanate Complex
1. Zero the spectrophotometer as described in A.
Spectrophotometer Zeroing. Prepare and record the
absorbance of a reagent blank as described in the B.
Blank Determination procedure (Ablk ).
2. Pipet 2.00 mL of the assayed 5 g/L Fe solution into a
500-mL volumetric flask containing 250 mL 0.1 N
nitric acid.
3. Fill the flask to volume with 0.1 N nitric acid. Stopper
and invert the flask 6 to 10 times to mix thoroughly.
4. Add 25 mL 2.5 N sulfuric acid and 10 mL of 40 g/L
potassium persulfate to a 100-mL volumetric flask.
Swirl to mix.
5. Pipet 2.00 mL of the solution (Step 3) into the flask
(Step 4) while swirling.
6. Add 25 mL of 200 g/L ammonium thiocyanate to the
flask while swirling. Dilute to volume with reagent
water. Stopper and invert the flask 6 to 10 times to
mix. Label the flask, STD 1.
7. Rinse the 1-cm silica cell 3 to 5 times with sample
from Step 6, and 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.
8. Record absorbance of sample at 477 nm as Astd 1.
Note: The absorbance should be recorded within
2 minutes of sample preparation.
9. Repeat Steps 4 to 8 and record absorbance of sample
at 477 nm as Astd 2.
10. Repeat Steps 4 to 8, substituting the following sample
sizes in Step 5 and record absorbance of results as
Ast2 1, Ast2 2, Ast3 1, etc.
STD # Sample Size
STD 2 5.0 mL
STD 3 10.0 mL
STD 4 15.0 mL
Calculation of Absorptivity
Absorptivity, L/(g-cm) =
Where:
(∆A477)(DF) Assay
∆A477 = (∆Astd # – ∆Ablk )
∆Astd # = absorbance for each STD measured at
477 nm
∆Ablk = absorbance of the blank measured at 477 nm
Dilution factor
(500)(100)
DF = for each
standard
=
(2.00)
500 mL = volume of first dilution
2.00 mL = volume of sample pipeted into first volumetric
flask
100 mL = volume of second dilution
STD
sample size
= volume of first dilution pipeted into second
volumetric flask
Assay = assay value determined for the 5 g/L STD Fe
solution
Typical Absorptivity
Fe STD # ∆A Absorptivity
STD 1 0.081
0.081
0.081
STD 2 0.200
0.199
0.200
STD 3 0.403
0.395
0.397
STD 4 0.597
0.601
X = 195.9
1s = 1.71
RSD = 0.9%
RSD should be =