Processing kodak motion picture films, module 3 analytical procedures

Spectrophotometric Determination of Iron (II) in “UL” Bleach
ECN-2-3275-2
INTRODUCTION
The determination of iron (II) in Process ECN-2 “UL”
bleach employs a spectrophotometric technique. The
iron (II) concentration is determined by adding sample to
deaerated 1,10-phenanthroline/sodium acetate to form a
colored complex. The absorbance of the complex is
measured at 510 nm on a spectrophotometer. Protect bleach
samples from oxidation between sampling and analysis to
avoid the accidental loss of iron (II). It is essential to
complete the analysis within four hours of sampling because
the ferric complex is thermally unstable and will yield
iron (II) when sealed samples are kept for extended periods.
The 1,10-phenanthroline/sodium acetate is deaerated with
nitrogen to prevent oxidation of the iron (II) in the sample as
the colored complex is formed.
Use of 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 three (3) replicates on each of the following
solutions during methods development.
1. A fresh “UL” bleach was prepared with all
components at their respective “working tank” aim
concentrations 0.492 g/L iron (II).
2. A seasoned “UL” bleach analyzed as received, at
0.270 g/L iron (II).
3. The same “seasoned” solution as in number 2, above,
was reanalyzed after making an analytically weighed,
standard addition of 0.483 g/L iron (II).
Sample
Fresh
0.492 g/L
Iron (II)
Seasoned
as Received
Seasoned
plus
Addition
Bias
Bias is a statistically significant deviation of the mean from
the known iron (II) 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 0.006 g/L iron (II) was found not to be
statistically significant fir the Process ECN-2 “fresh” tank
“UL” bleach sample. However, the difference at the
95 percent confidence level 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
98.96 percent and found to not 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
Iron II
Mean
g/L Iron (II) N
Repeatability
Standard
Deviation,
1s r
g/L Iron (II)
95 Percent
Confidence
Estimate
g/L Iron (II)
0.498 4 0.002 ± 0.006
0.270 4 0.004 ± 0.013
0.748 4 0.016 ± 0.051