Processing kodak motion picture films, module 3 analytical procedures

Reference Electrode Care/Rejuvenation
For new reference electrodes, withdraw the filling solution
and refill the electrode with 3.5 M KCl (calomel electrodes)
or 3.5 M KCl saturated with AgCl (Ag/AgCl electrodes).
At the beginning of each shift/day, the KCl filling solution
should be withdrawn and the electrode refilled with fresh
3.5 M KCl (calomel electrodes) or 3.6 M KCl saturated with
AgCl (Ag/AgCl electrodes).
When poor performance of the pH measurement system is
not improved with substitution of a new pH electrode,
reference electrode junction clogging may be the problem,
especially where inaccurate or unsteady readings are
obtained. If there is a possibility the filling solution may have
become contaminated, refill with fresh KCl and recheck the
system. Frit-type junctions can be checked for flow by
pressing just the tip of the reference electrode gently against
a paper towel several times. A small wet spot will be visible
if the junction is flowing.
For clogged calomel reference electrodes, warm (not
above 50°C) a solution of 3.5 M KCl diluted 1 part to 9 with
distilled water, and soak the electrode junction for 1/2 hour.
Drain the electrolyte and replace with fresh 3.5 M KCl, and
retest the electrode.
For Ag/AgCl reference electrodes, a 10-minute soak in
10 percent NH 4OH can remove precipitated AgCl from the
junction. It is important that the electrode have filling
solution present when trying this procedure. Higher
concentrations of NH 4OH or longer periods of soaking
should be avoided as in some types of Ag/AgCl reference
electrodes damage to the reference element may occur.
As with glass electrodes, more severe procedures are not
recommended as they are costly and, in many cases, do more
to damage the electrode than to improve its performance.
Reference Electrode Accuracy Check
Liquid-junction potential error in reference electrodes can be
assessed * by determining the pH of the NIST equimolar
phosphate buffer (See pH 7 Equimolar Phosphate Reference
Buffer in APPENDIX A) at two ionic strengths differing by a
factor of 10. The meter is standardized with the NIST
phosphate buffer (pH 7, full strength), and the NIST
phthalate buffer (pH 4) as in APPENDIX B. Dilute 110 mL
of the NIST phosphate buffer (pH 7) to 1 L with distilled
water, and measure the pH of the diluted buffer. The meter
reading should be 7.065 ± 0.010 pH units for a properly
functioning reference junction. †
* J.A. Illingsworth, A Common Source of Error in pH Measurements;
Biochem. J. (1981) 195, 259.
† Additional methods for reference electrode evaluation can be found in:
C.C. Westcott pH Measurements; Academic Press: New York (1978)
pp. 65-70.
APPENDIX D
RECOMMENDED COMMERCIALLY
PREPARED BUFFER SOLUTIONS AND THEIR
SOURCES
NIST Reference Buffers
1. pH 1.68, 500 mL, Radiometer America Order No.
511M001
2. pH 4.01, 500 mL, Radiometer America Order No.
511M002 (European No. S1316)
3. pH 6.86, 500 mL, Radiometer America Order No.
511M003 (European No. S1346)
4. pH 9.18, 500 mL, Radiometer America Order No.
511M006 (European No. S1336)
In the U.S., above buffers are available from:
Radiometer America
810 Sharon Drive
Westlake, OH 44145
1-800-736-0600
In Europe, they are manufactured by and available from:
Radiometer A/S
Emdrupvjet 72
Copenhagen NV
Denmark
Calibrating Buffers
1. pH 4, 20-L cube, VWR Scientific, CAT No. 34170-155
2. pH 7, 20-L cube, VWR Scientific, CAT No. 34170-158
VWR Scientific
P.O. Box 483
Bridgeport, NJ 08014
800-932-5000
3. pH 10,20-L cube, Fisher Scientific, CAT No.
SB-115-20
Fisher Scientific Company
50 Fadem Road
Springfield, NJ 07081-3193
800-766-7000
Control Buffers
1. pH 3.63, gallon, SPI CAT No. 1750
Also available in 120-mL and quart volumes
2. pH 11.43, gallon, SPI CAT No. 6805
Also available in 120-mL and quart volumes
These control buffers are manufactured for Kodak by:
Solution Plus, Inc.
2275 Cassens Drive, Suite 147
Fenton, MO 63026
314-349-4922
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03 11