Processing kodak motion picture films, module 3 analytical procedures

Potentiometric Determination of Bromide in Ferricyanide Bleach
ECN-0004/1
ECP-0004/1
ECR-0004/1
Process ECN-2 ECP-2D VNF-1/LC RVNP
Formulas SR-29 SR-27 SR-40 —
INTRODUCTION
The ferricyanide and ferrocyanide ions in the bleach sample
are precipitated using zinc sulfate and removed by
centrifugation or filtration. A portion of the resulting
solution is then titrated potentiometrically with silver nitrate
solution.
The bleach has no chloride in its formula. However,
chloride ions may be present in the water, or as an impurity
in other chemicals. Because there is usually only a small
amount of chloride present, the individual chloride and
bromide “S” shaped curves (“breaks”) tend to merge (see
Figure 1). To separate them satisfactorily, more chloride is
added prior to titration. In the resulting titration record, the
first “break” is due to the bromide while the second (if the
titration is allowed to continue) is due to the chloride.
Figure 1 S-shaped Curves
20
30
150 mV
40
OmV
50
60
70
80
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.
90
12.0
10.0
8.0
4.0 6.0
mL 0.05 NAgNO3
2.0
0.0
F002_0888AC
PRECISION AND BIAS
Repeatability Standard Deviation, 1sr and 95
Percent Confidence Estimate (not including Bias)
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, the analyst who
developed this method performed five (5) replicates on each
of the following solutions:
a. A fresh ferricyanide bleach prepared with all
components at their respective aim working tank
concentrations.
b. A seasoned ferricyanide bleach analyzed, as received, at
17.805 g/L NaBr.
c. The same seasoned solution as in number b, above,
analyzed after making an analytically weighed, standard
addition of 9.248 g/L NaBr.
Sample
“Fresh” at
“Aim”
(17.029 g/L
NaBr)
“Seasoned”,
As
Received
“Seasoned”
with
Standard
Addition
Mean
Level
(g/L NaBr)
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03 1
(N)
Repeatability
Standard
Deviation, 1s r
(g/L NaBr)
95 Percent
Confidence
Estimate
16.606 5 0.20 ± 0.55
17.805 5 0.33 ± 0.92
26.725 5 0.56 ± 0.36