Processing kodak motion picture films, module 3 analytical procedures

APPENDIX 1
Determination of the Absorptivity of the
Iron-Thiocyanate Complex
Note: Use this procedure to recheck the iron thiocyanate
absorptivity at least every six months. Also use it the first
time this method is performed and whenever the
spectrophotometer has been adjusted or repaired.
Reagents
All reagents are ACS Reagent Grade unless otherwise stated.
2.5 N Sulfuric Acid, H 2 SO 4
40 g/L Potassium Persulfate, K 2 S 2 O 8
200 g/L Ammonium Thiocyanate, NH 4 SCN
Ferric Nitrate, 9-hydrate, Fe(NO 3 ) 3 9H 2 O
Potassium Iodide, KI
Hydrochloric Acid, concentrated, HCl
Starch Indicator
0.1 N Sodium Thiosulfate, Na 2 S 2 O 3
(standardized to 4 decimal places)
0.10 N Nitric Acid, HNO 3
Procedure
Standard Iron Solution Preparation
1. Weigh 9.0 ± 0.001 g ferric nitrate, 9-hydrate and
transfer to a 250-mL volumetric flask.
2. Dissolve and dilute to volume with reagent water.
3. Stopper and invert the flask 6 to 10 times to mix. Label
this flask 5 g/L Fe solution.
Solution Assay
1. Pipet 25.0 mL of 5 g/L Fe solution into a 500-mL
glass-stoppered Erlenmeyer flask containing 100 mL
of reagent water.
2. Add 5 mL of concentrated hydrochloric acid and
3 ± 0.1 g of potassium iodide.
3. Stopper and swirl the flask to dissolve the potassium
iodide. Place in a dark area for 30 minutes.
4. After 30 minutes, remove the flask from the dark.
Begin titrating with standardized 0.1 N sodium
thiosulfate until the red color changes to a yellow-red
color.
5. Add 3 mL starch indicator and continue titrating until
the solution changes from blue to colorless and
remains so for 15 seconds. Record the mL of 0.1 N
sodium thiosulfate as mLspl .
6. Repeat Steps 1 to 5 two more times. Record the mL of
0.1 N sodium thiosulfate as stated in Step 5.
7. Then repeat Steps 1 to 5 without the 5 g/L Fe solution
and record the mL of 0.1 N sodium thiosulfate as
mLblk .
Calculation
Note: Calculate the assay result separately for each of the
three sample titrations.
g/L Fe =
Where:
Calculate the mean iron content (Xbar), standard
deviation (s) and RSD of the assay using the data from the
three analyses of the standards. The mean value should have
an RSD < 0.10%.
Where:
(∆mL)(eq wt Fe)(N Na 2 S 2 O 3 )(1000)
(sample size)(1000)
(∆mL)(55.85)(N Na 2 S 2 O 3 )(1000)
(25.0)(1000)
2.23(∆mL)(N Na 2S 2O 3)
∆mL = mL spl – mL blk
1000 = Conversion of millilitres to litres and milligrams to
grams
X = X n
X = individual g/L Fe assay results
n = the number of replicates (3)
4 Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03
s =
RSD* = s
X
(X - X)
n-1
2
x 100%
=
=
F010_0087AC