Processing kodak motion picture films, module 3 analytical procedures

Spectrophotometric Determination of Total Iron in “UL” Bleach
ECN-2-3263-2
INTRODUCTION
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.
PRECISION AND BIAS
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).
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.
Sample
Mean
(g/L Total
Iron
Total Iron
N
Repeatability
Standard
Deviation,
1s r
(g/L Total
Iron
95 Percent
Confidence
Estimate
(g/L Total
Iron)
Fresh 3.78 4 0.025 ± 0.08
Seasoned
as received
Seasoned
4.91 4 0.030 ± 0.10
plus
Addition
5.76 4 0.033 ± 0.11
Bias
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.
Recovery
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.
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03 1