Download ECN-2-3263-2

Spectrophotometric Determination of Total Iron in “UL” Bleach
ECN-2-3263-2
INTRODUCTION
Bias
The determination of total iron in Process ECN-2, “UL”
bleach, utilizes a spectrophotometric technique. The total
iron concentration is determined by oxidizing any iron (II)
present to iron (III) with persulfate. A thiocyanate complex
of the iron (III) is formed in a dilute acid solution. A direct
measurement of the iron-thiocyanate complex is made using
a calibrated spectrophotometer at 477 nm.
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.
Bias is a statistically significant deviation of the mean from
the known ammonium total iron level at a 95 percent
confidence level. It is determined for fresh samples only.
Bias was not determined for this sample because the
component concentration level was not determined
independently of the test method.
A bias of –0.09 g/L total iron was found to be statistically
significantly different for the Process ECN-2 “fresh” tank
“UL” bleach sample. However, the difference was judged
not to be practically significant.
PRECISION AND BIAS
Recovery is used instead of bias for seasoned samples, since
the component concentration level was not determined
independently of the test method. It is defined as the
calculated mean for the seasoned sample with a standard
addition of the component minus the mean for the seasoned
sample, divided by the actual amount of the standard
addition. It is expressed as a percentage.
The recovery of the standard addition sample was
85.86 percent and found to be statistically different from
100 percent at the 95 percent confidence level. However, it
was judged not to be practically different from 100 percent.
Repeatability Standard Deviation, 1sr and
95 Percent Confidence Estimate
Repeatability standard deviation is an estimate of the
variability one trained analyst should be able to obtain under
favorable conditions (analyzing a sample, with one
instrument, within one day).
The 95 percent confidence estimate (calculated using the
repeatability standard deviation) around a single test result
will include the mean value 95 percent of the time.
To obtain the repeatability data, a single skilled analyst
performed two (2) replicates on each of the following
solutions over two days during methods development.
1. A fresh “UL” bleach was prepared with all
components at their respective “working tank” aim
concentrations (3.87 g/L total iron).
Recovery
2. A seasoned “UL” bleach analyzed as received, at
4.91 g/L total iron.
3. The same “seasoned” solution as in number 2, above,
was reanalyzed after making an analytically weighed,
standard addition of 0.99 g/L total iron.
Total Iron
Sample
Mean
(g/L Total
Iron
N
Repeatability
95 Percent
Standard
Confidence
Deviation,
Estimate
1sr
(g/L Total
(g/L Total
Iron)
Iron
Fresh
3.78
4
0.025
± 0.08
Seasoned
as received
4.91
4
0.030
± 0.10
Seasoned
plus
Addition
5.76
4
0.033
± 0.11
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures • H24.03
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REPRODUCIBILITY
Bias
Customer Standard Deviation, 1sc and
95 Percent Confidence Estimate
Reproducibility, or customer standard deviation, (1sc) is an
estimate of the variability a customer could expect when
submitting a sample to any Photoprocessing Quality
Services laboratory, where any trained analyst could test the
sample using any instrument on any day.
The 95 percent confidence estimate (calculated using the
customer standard deviation) around a single test result will
include the mean value 95 percent of the time.
Five Process ECN-2 “UL” bleach samples were analyzed
by four analysts, on two different days. Duplicate analyses
were performed on each sample, on each of the two days.
These samples were:
1. Three “fresh” “UL” bleach samples were prepared
with all components at their respective “working tank”
aim concentrations.
2. A “seasoned” “UL” bleach sample was analyzed
spectrophotometrically as received, at 4.91 g/L total
iron.
3. The same “seasoned” solution as in number 2, above,
was reanalyzed after making an analytically weighed,
standard addition of 0.99 g/L iron.
Total Iron
N
Mean
“Fresh” at
1.05 g/L
Total iron
16
1.00 g/L
“Fresh” at
3.87 g/L
Total iron
16
3.78 g/L
0.037
± 0.08
“Fresh” at
7.48 g/L
Total iron
16
7.46 g/L
0.056
± 0.13
“Seasoned”
As
Received
16
4.91 g/L
0.032
± 0.07
2
Recovery
Recovery is used instead of bias for seasoned samples, since
the component concentration level was not determined
independent of the test method. It is defined as the calculated
mean for the seasoned sample with a standard addition of the
component minus the mean for the seasoned sample, divided
by the actual amount of the standard addition. It is expressed
as a percentage.
The recovery of the standard addition sample was
83.84 percent and found to be statistically different from
100 percent at the 95 percent confidence level. However, it
was judged not to be practically different from 100 percent.
APPARATUS
95 Percent
Reproducibility
Confidence
Standard
Estimate
Deviation, 1sc
(g/L Total
(g/L Total Iron)
Iron)
Sample
“Seasoned”
with
Standard
Addition
Bias is a statistically significant deviation of the mean from
the known total iron level at a 95 percent confidence level. It
is determined for fresh samples only. Bias was not
determined for this sample since the component
concentration level was not determined independently of the
test method.
A statistically significant low bias of -0.05 g/L and
-0.09 total iron was found for the fresh “UL” bleach tank
sample at the 1.05 g/L and 3.87 g/L iron level (aim),
respectively. However, the bias was judged not to be
practically significant. A bias of -0.02 g/L at the 7.48 g/L
total iron was not statistically significant.
0.019
± 0.04
All volumetric glassware should meet all Class A
specifications, as defined by American Society for Testing
and Materials (ASTM) Standards E 287, E 288, and E 969,
unless otherwise stated.
• Double Beam Spectrophotometer with a tungsten lamp
(i.e., Perkin-Elmer Lambda 4 series)
• 1-cm Silica Cells
16
5.74 g/L
0.038
± 0.08
REAGENTS
All reagents should be ACS Reagent Grade unless otherwise
specified.
• 2.5 N Sulfuric Acid, H2SO4
• 40 g/L Potassium Persulfate, K2S2O8
• 200 g/L Ammonium Thiocyanate, NH4SCN
• Water, Type I Reagent - This method was developed using
reagent water equivalent to or purer than Type I grade, as
defined in ASTM Standard D 1193. Other grades of
water, e.g., reverse osmosis (RO), demineralized, or
distilled water, may give equivalent results, but the effects
of water quality on method performance have not been
studied.
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures • H24.03
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.
Calculations
∆A477 = Aspl – Ablk
g/L Fe
=
(∆A477)(DF)
(Absorptivity)
=
Where:
DF =
(250 mL)(100 mL)
Dilution
=
factor
=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)
Note: Use APPENDIX 1 to determine the absorptivity of the
iron-thiocyanate complex. Each spectrophotometer may
yield a different absorptivity value.
Example Calculation:
∆A477 = Aspl – Ablk
∆A477 = 0.479 – 0.043 = 0.436
g/L Fe
=
(∆A477)(DF)
(Absorptivity)
(0.436)(1666)
(196)
=
= 3.7
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.
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures • H24.03
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APPENDIX 1
Calculation
Determination of the Absorptivity of the
Iron-Thiocyanate Complex
Note: Calculate the assay result separately for each of the
three sample titrations.
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.
g/L Fe
=
(∆mL)(eq wt Fe)(N Na2S2O3)(1000)
(∆mL)(55.85)(N Na2S2O3)(1000)
Reagents
All reagents are ACS Reagent Grade unless otherwise stated.
• 2.5 N Sulfuric Acid, H2SO4
• 40 g/L Potassium Persulfate, K2S2O8
• 200 g/L Ammonium Thiocyanate, NH4SCN
(sample size)(1000)
(25.0)(1000)
=
=
2.23(∆mL)(N Na2S2O3)
Where:
• Ferric Nitrate, 9-hydrate, Fe(NO3)3•9H2O
∆mL = mLspl – mLblk
• Potassium Iodide, KI
1000 = Conversion of millilitres to litres and milligrams to
grams
• Hydrochloric Acid, concentrated, HCl
• Starch Indicator
• 0.1 N Sodium Thiosulfate, Na2S2O3
(standardized to 4 decimal places)
• 0.10 N Nitric Acid, HNO3
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%.
X = nX
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.
(X - X) 2
n-1
s=
RSD* = s x 100%
X
F010_0087AC
Where:
X = individual g/L Fe assay results
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.
n = the number of replicates (3)
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.
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Processing KODAK Motion Picture Films, Module 3, Analytical Procedures • H24.03
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.
Calculation of Absorptivity
STD #
Sample Size
STD 2
5.0 mL
STD 3
10.0 mL
STD 4
15.0 mL
Assay
Where:
∆A477 = (∆Astd # – ∆Ablk)
∆Astd # = absorbance for each STD measured at
477 nm
∆Ablk = absorbance of the blank measured at 477 nm
DF =
Dilution factor
for each
standard
(500)(100)
=
(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 = volume of first dilution pipeted into second
sample size
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
198.0
198.0
198.0
STD 2
0.200
0.199
0.200
195.6
195.6
195.6
STD 3
0.403
0.395
0.397
197.0
193.1
194.1
STD 4
0.597
0.601
194.6
195.9
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.
(∆A477)(DF)
Absorptivity, L/(g-cm) =
X = 195.9
1s = 1.71
RSD = 0.9%
RSD should be = <1.0%
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures • H24.03
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