Kodak ECN-0002-1 User Manual

Titrimetric Determination of Hypo Index, Thiosulfate, and Sulfite in EASTMAN Color Films,
Process ECN-2 Fixer

ECN-0002/1

Process ECN-2 ECP-2D VNF-1/LC RVNP

Formulas F-34a/F-34aR — — —

INTRODUCTION

This method describes the titrimetric determination of hypo
index (total reductants), thiosulfate, and sulfite in
EASTMAN Color Films, Process ECN-2, fixers. It is
recommended that these determinations be carried out by a
potentiometric titrimetric approach, using an auto-titrator.
However, for those unable to use instrumentation, the
manual titrimetric technique, using the visual starch
indicator, is included.

For the potentiometric measurement, a Metrohm
Potentiograph, Model E536 or equivalent should be us ed.
The potentiometric titration requires a platinum indicator
electrode and a double-junction reference electrode.

The Hypo Index (HI) or total reductants of a fixer is
defined as the millilitres of 0.1 N iodine consumed by the
thiosulfate and sulfite combined (reaction 1 & 2), in a
specified volume of fixer. The fixer is added to an excess of
iodine (liberated from the reaction of potassium iodate and
potassium iodide under acidic conditions - reaction 3). The
unreacted iodine is titrated either potentiometrically or
visually with standardized sodium thiosulfate from the
appropriate capacity burette. The difference between the
blank titration and the sample titration represents the
milliequivalents of iodine consumed by the sample.
Dividing the milliequivalents of iodine by 0.1 meq/mL
yields the HI of the sample. Hypo index is reported in the
terms of HI(1), mL which is the millilitres of 0.1000 N I
consumed by 1.0 mL of sample.

2

The thiosulfate is determined by the visual titration by

adjusting the pH of a sample aliquot to 8.5. At this pH, the
sulfite rapidly forms the stable sulfite - formaldeh yde
adduct. Upon acidification, which prevents the adduct from
reacting with iodine, the thiosulfate from the sample is
titrated with standardized iodine reagent to a starch end
point.

The sulfite content is calculated by subtracting the

milliequivalents of iodine consumed by the thiosulfate from
the milliequivalents of iodine consumed by the thiosulfate
and sulfite. The sulfite is reported as sodium sulfite.

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

To obtain the repeatability data, a single skilled analyst
performed five (5) replicates on each of the following
solutions (this procedure was done by both potentiometric
and visual end point detection):

a. A “fresh” EASTMAN Color Films, Process ECN-2,

Fixer prepared with all components at their respective
aim concentrations in a working tank.

b. A “seasoned” EASTMAN Color Films, Process ECN-2,

Fixer analyzed as received at 125.67 g/L thios ulfate ion
and 28.92 g/L sodium sulfite.

c. The same “seasoned” solution as in number b, above,

reanalyzed after making standard additions of

37.850 g/L thiosulfate ion and 8.415 g/L sodium sulfite.

2 S

=

+ I2 → 2I- + S4O

2O3

=

6

(reaction 1)

Reproducibility

Three EASTMAN Color Films, Process ECN-2, Fixer

=

+ I2 + H2O → SO

HSO

3

=

+ 2I- + 3H

4

+

(reaction 2)

samples were analyzed by four analysts, each us ing different
titration stations, on two different days. Each analyst
analyzed each sample by both the potentiometric and the

-

+ 5I- + 6H+ → 3I2 + 3H2O (reaction 3)

IO

3

visual end point technique. Duplicate analyses were
performed on each sample, on each of the two days. These
samples were:

Na

adding 6 percent formaldehyd e to a second sample aliquo t in
reagent water. Under these conditions, the sulfite in the
sample forms a formaldehyde bisulfite complex (reaction 4).
This sample is then added to an excess of acidified iodine.
The unreacted iodine is titrated either potentiometrically
with standardized sodium thiosulfate from a 50-mL capacity
burette. The difference between the blank titration and the
sample titration represents the milliequivalents of iodine
consumed by the thiosulfate in the sample. The thiosulfate is
expressed as g/L thiosulfate ion (S

+ HCHO + H2O → CH3(OH) SO3Na + NaOH (reaction 4)

2SO3

The thiosulfate is determined potentiometrically by

=

).

2O3

a. a “fresh” tank solution prepared at 109.212 g/L

thiosulfate ion and 21.335 g/L sodium sulfite.

b. an EASTMAN Color Films, Process ECN-2 “seasoned”

tank fixer sample analyzed, as received, in the same
manner as the “fresh” fixer.

c. the same (as in number b, above) EASTMAN Color

Films, Proces s EC N -2 “seasoned” tank fixer sample
reanalyzed in the same manner as the “fresh” fixer, after
standard additions of thiosulfate and su lfite were mad e.
The “seasoned” sample of EASTMAN Color Films,
Process ECN-2 fixer, analyzed to be 115.17 g/L
thiosulfate ion and 15.69 g/L sodium sulfite. Standard

Processing KODAK Motion Picture Films, Module 3, Analytical Procedures • H24.03 1

additions of 34.57 g/L thiosulfate ion and 5.444 g/L
sodium sulfite were made to that “seasoned” sample.

POTENTIOMETRIC TITRATION STATISTICS

Repeatability Standard Deviation, 1sr & 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 will
include the mean value 95 percent of the time.

HYPO INDEX (1 mL)

Samples

(Process ECN-2 Fixer)

“Fresh” at “Aim” 10.02 5 0.086 ± 0.24
“Seasoned”, As

Received

“Seasoned” with

Standard Addition

Mean Level

(mL 0.1 N I

15.80 5 0.073 ± 0.20

19.38 5 0.14 ± 0.39

(N)

)

2

Repeatability

Standard Deviation, 1S

(mL 0.1 N I2)

Confidence Estimate

r

95 Percent

(mL 0.1 N I

)

2

THIOSULFATE

Samples

(Process ECN-2 Fixer)

“Fresh” at “Aim” 81.18 5 0.67 ± 1.9
“Seasoned”, As

Received

“Seasoned” with

Standard Addition

Samples

(Process ECN-2 Fixer)

“Fresh” at “Aim” 17.55 5 0.69 ± 1.9
“Seasoned”, As

Received

“Seasoned” with

Standard Addition

Mean Level

(g/L S

2O3

125.67 5 0.47 ± 1.3

153.79 5 0.60 ± 1.7

Mean Level

(g/L Na

28.92 5 0.65 ± 1.8

35.69 5 1.18 ± 3.3

2SO3

=

)

)

(N)

SULFITE

(N)

Repeatability

Standard Deviation, 1S

(g/L S2O

Repeatability

Standard Deviation, 1S

(g/L Na2SO3)

=

)

3

Confidence Estimate

r

Confidence Estimate

r

Bias

Bias is a statistically significant deviation of the mean from
the known mix level at a 95 percent confidence level. It is
determined for “fresh” samples only. Bias is not determined
for “seasoned” samples, since the component concentration
level was not determined independently of the test method.

A statistically significant bias for thiosulfate of
(-1.09 percent) was found for a “fresh” tank Process ECN-2
Fixer sample. The biases fo r Hypo Index and Sodi um Sulfite
were not statistically significant. However, the bias for
thiosulfate was judged not to be practically significant.

95 Percent
(g/L S

2O3

95 Percent

(g/L Na

2SO3

=

)

)

2 Processing KODAK Motion Picture Films, Module 3, Analytical Procedures • H24.03

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, divi ded by the actual am ount of
the standard addition. It is expressed as a percentage. The table below
shows whether or not a recovery is statistically or practically different
from 100 percent.

POTENTIOMETRIC RECOVER Y, Process ECN-2

Analyte Recovery Value Statistically Significant Practically Significant

Hypo Index (1 mL) 76% Yes No
Thiosulfate (S
Sodium Sulfite (Na

=

)74% Yes No

2O3

) 80.4% No No

2SO3

Reliability
Customer Standard Deviation, 1s

& 95 Percent

c

Confidence Estimate (not including bias)

The customer standard deviation is an estimate of the variability a
customer could expect when submitting a sample to any
Photoprocessing Quality Services laboratory, where any trained
analyst could test the sample using any instrument on any day.

The 95 percent confidence estimate (calculated using the customer
standard deviation) around a single test result will include the mean
value 95 percent of the time.

HYPO INDEX

Samples (Process

ECN-2 Fixer)

Mean Level

(mL 0.1 N I

(N)

Reproducibility

2

(mL 0.1 N I2)

Standard Deviation, 1S

)

c

95 Percent

Confidence Estimate

(mL 0.1 N I

“Fresh” at “Aim” 12.88 16 0.25 ± 0.54
“Seasoned”, As

Received

“Seasoned” with

Standard Addition

12.73 16 0.13 ± 0.27

15.83 16 0.16 ± 0.33

THIOSULFATE

Samples (Process

ECN-2 Fixer)

Mean Level

(g/L S

2O3

(N)

Reproducibility

=

)

Standard Deviation, 1S

(g/L S2O

=

)

3

c

95 Percent

Confidence Estimate

(g/L S

“Fresh” at “Aim” 108.14 16 0.94 ± 2.00
“Seasoned”, As

Received

“Seasoned” with

Standard Addition

Samples (Process

ECN-2 Fixer)

114.86 16 0.73 ± 1.56

142.23 16 0.78 ± 1.67

)

2SO3

Reproducibility

(g/L Na2SO3)

Confidence Estimate

c

(g/L Na

Mean Level

(g/L Na

2SO3

SULFITE (Na

(N)

Standard Deviation, 1S

)

95 Percent

“Fresh” at “Aim” 20.79 15 0.59 ± 1.26
“Seasoned”, As

Received

“Seasoned” with

Standard Addition

15.70 16 0.68 ± 1.4 5

19.85 16 0.76 ± 1.6 3

2O3

2SO3

)

2

=

)

)

Processing KODAK Motion Picture Films, Module 3, Analytical Procedures 3