Processing kodak motion picture films, module 3 analytical procedures

Potentiometric Determination of Ammonium Bromide in UL Bleach
ECN-0022/1
INTRODUCTION
The ammonium bromide (NH 4 Br) level in Process ECN-2
“UL” Bleach is determined potentiometrically by a silver
nitrate titration. An aliquot of bleach sample is diluted with
reagent water. An aliquot of the diluted sample is then
combined with sulfuric acid and reagent water and it is then
titrated on an automatic titrator with standardized silver
nitrate. A silver sulfide ion-selective indicator electrode
(ISE) and a double-junction reference electrode are used to
determine the end point. It was found that when using a
silver bar indicator electrode, a conditioning layer had to be
deposited on the electrode surface or a double inflection was
seen. Using the silver sulfide ion-selective electrode
eliminated this problem. All precision and bias data were
generated using a silver sulfide ion-selective electrode.
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 (25.4255 g/L NH4Br). 2. A seasoned “UL” bleach analyzed potentiometrically
as received, at 40.171 g/L NH4Br). Sample
Bias
Bias is a statistically significant deviation of the mean from
the known ammonium bromide 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 –0.0325 g/L NH 4 Br was found not to be
statistically significant fir the Process ECN-2 “fresh” tank
bleach sample.
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03 1
NH 4 Br
Mean
(g/L NH 4 Br) N
Repeatability
Standard
Deviation,
1s r
(g/L NH 4Br)
95 Percent
Confidence
Estimate
(g/L NH 4 Br)
Fresh 25.393 3 0.042 ± 0.181
Seasoned
as received
40.171 3 0.083 ± 0.357