Processing kodak motion picture films, module 3 analytical procedures
Processing kodak motion picture films, module 3 analytical procedures
Processing kodak motion picture films, module 3 analytical procedures
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Potentiometric Determination of Silver in Process ECN Fixing Baths<br />
ECN-0023-01<br />
INTRODUCTION<br />
The sample containing silver is titrated potentiometrically<br />
with standardized sodium sulfide using a silver billet/double<br />
junction electrode pair. The sample is made alkaline to<br />
prevent the decomposition of sodium thiosulfate, which<br />
occurs in acid solutions. Ethylenedinitrilotetraacetic acid<br />
(EDTA) is added to minimize interference of other metal<br />
ions. The EDTA reagent does not prevent interference from<br />
zinc ions. Gelatin is added to prevent the coagulation of the<br />
silver sulfide that is formed. This prevents the coagulated<br />
silver sulfide from occluding the silver ions.<br />
Changes in the volume of sample and of sodium<br />
hydroxide/EDTA reagent affect the silver results. If a small<br />
amount of sample is used, the sample volume must be<br />
adjusted to about 300 mL with 1.0 M sodium thiosulfate.<br />
Use of this method requires handling potentially<br />
hazardous chemicals. Material Safety Data Sheets (MSDS)<br />
should be consulted for each chemical before use. These can<br />
be obtained from each chemical supplier.<br />
PRECISION AND BIAS<br />
A. Repeatability Standard Deviation, 1sr and<br />
95 Percent Confidence Estimate (not including<br />
Bias)<br />
Repeatability standard deviation is an estimate of the<br />
variability one trained analyst should be able to obtain under<br />
favorable conditions (analyzing a sample, with one<br />
instrument, within one day).<br />
The 95 percent confidence estimate (calculated using the<br />
repeatability standard deviation) around a single test result<br />
will include the mean value 95 percent of the time.<br />
To obtain the repeatability data, a single skilled analyst<br />
performed three (3) replicates on each of the following<br />
solutions during methods development.<br />
1. A “fresh” fixing tank prepared with all components at<br />
their respective “working tank” aim concentrations.<br />
2. The same “fresh” solution as in number 1, above,<br />
reanalyzed after making an <strong>analytical</strong>ly weighed,<br />
standard addition of 1.0745 g/L Ag.<br />
3. A “seasoned” fixing tank analyzed potentiometrically<br />
as received, at 1.1488 g/L Ag.<br />
4. The same “seasoned” solution as in number 3, above,<br />
reanalyzed after making an <strong>analytical</strong>ly weighed,<br />
standard addition of 0.2686 g/L Ag.<br />
Sample<br />
Mean<br />
(g/L Ag)<br />
Bias<br />
Bias is a statistically significant deviation of the mean from<br />
the known mix level at a 95 percent confidence level. It is<br />
determined for fresh samples only. Bias was not determined<br />
for this sample because the component concentration level<br />
was not determined independently of the test method.<br />
Instead, a recovery was calculated for the component in a<br />
fresh sample.<br />
The recovery of 106.23 percent was not significantly<br />
different from 100 percent at the 95 percent confidence<br />
level.<br />
Recovery<br />
Recovery is used for seasoned samples, since the component<br />
concentration level was not determined independently of the<br />
test method. It is defined as the calculated mean for the<br />
seasoned sample with a standard addition of the component<br />
minus the mean for the seasoned sample, divided by the<br />
actual amount of the standard addition. It is expressed as a<br />
percentage.<br />
The recovery of 102.16 percent* was not statistically<br />
significantly different from 100 percent at the 95 percent<br />
confidence level.<br />
* Note: Recovery was calculated by accounting for a<br />
5 percent error from dilution of 1 liter of seasoned fixer by a<br />
50.00 mL aliquot of silver nitrate.<br />
<strong>Processing</strong> KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03 1<br />
Ag<br />
N<br />
Repeatability<br />
Standard<br />
Deviation, 1s r<br />
(g/L Ag)<br />
95 Percent<br />
Confidence<br />
Estimate<br />
(g/L Ag)<br />
“Fresh”<br />
“Fresh” plus<br />
0.0060 3 0.00000 ± 0.0000<br />
Standard<br />
Addition<br />
“Seasoned”,<br />
1.0830 3 0.00251 ± 0.0108<br />
As<br />
Received<br />
“Seasoned”<br />
1.1488 3 0.00374 ± 0.0161<br />
plus<br />
Standard<br />
Addition<br />
1.3658 3 0.00492 ± 0.0212<br />
Example:<br />
(1.3658) - (1.1488 x 0.95) x 100 = 102.16%<br />
0.2686