Processing kodak motion picture films, module 3 analytical procedures

Potentiometric Determination of Iodide in Reversal Color Developers
ECR-925A
Process ECN-2 ECP-2D VNF-1/LC RVNP
Formulas — — DR-150/151 * DR-150
* This method was developed for a process other than VNF-1 and RVNP
that did not contain sodium thiocyanate. Thiocyanate is a well-known
interferent to halide determinations when using a silver ion titration, due
to co-precipitation. A significant high bias could exist when applying this
procedure to determine bromide in developers containing thiocyanate.
PRINCIPLE
A sample of developer is made highly alkaline to prevent the
formation of an emulsion during the extraction of CD-3 and
RA-1 with chloroform. After the extraction, the aqueous
phase is acidified with glacial acetic acid. The solution is
then titrated potentiometrically with a silver nitrate solution
using silver billet and double junction electrodes. The
inflection point is determined by applying the concentric
arcs technique.
The addition of sodium chloride alters the shape of the
potentiometric curve such that the end point determined by
this technique is slightly beyond the actual inflection point.
However, the concentric arcs technique is used because it
produces more reliable results than other techniques for
determining the location of the end point. The difference
between the determined end point and the actual inflection
point is fairly constant and is calibrated out. See Figure 1 for
a typical titration curve.
Figure 1 Typical Iodide Titration Curve in Reversal
Color Developers
mV
1100
1000
900
800
700
0 5.00 10.00 15.00 20.00
F002_0939AC
mL Standardized 0.005 N Silver Nitrate
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.
This method uses chloroform-a highly toxic solvent and
suspected carcinogen. The following strict precautions must
be observed when using chloroform:
1. An exhaust (fume) hood must be used that provides
100-ft/min minimum average air face velocity. The
greatest laboratory hazard presented by chloroform is
through inhalation. The odor threshold of chloroform
(50 ppm) is much higher than its threshold limit value
(TLV) of 2 ppm. Therefore, since there is no odor
warning, toxic levels can be present without an
analyst's awareness.
2. Impervious gloves should be worn when handling
chloroform. Chloroform can cause defatting, and
subsequent cracking of the skin. In addition, this
defatting can make the skin more susceptible to
dermatitis from other sources.
3. Eye protection, in the form of safety glasses or goggle
must be worn by the analyst. Chloroform vapors can
cause irritation of the eye—especially to the
conjunctiva (the eye's membrane covering). Splashing
of the liquid into the eye can be painful. If it occurs
despite precautions, wash the eye immediately and
seek medical attention.
4. Keep chloroform away from heat and open flames.
Although not a flammable substance, chloroform may
break down to phosgene (COCl2 ), which further
decomposes to hydrochloric acid and carbon
monoxide after inhalation into the body.
5. Local regulations must be adhered to regarding the
use and/or disposal of chloroform. Regulations
concerning chloroform use may vary from one locality
to another. It is the responsibility of the laboratory
supervisor to be aware of, and follow, these
regulations.
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03 1