Thermo Fisher Scientific Ion Selective Electrodes Cyanide - Manual (Page 11)

Instruction Manual Cyanide Electrode
11
TABLE 4: Temperature vs. Values for the Electrode Slope
Temp.(
o
C) "S"
0 54.20
10 56.18
20 58.17
25 59.16
30 60.15
40 62.13
50 64.11
If changes in temperature occur, the electrodes should be re-calibrated.
The temperature range for the cyanide electrode is 0
o
-80
o
C, provided that temperature equilibrium
has occurred. If the temperature varies substantially from room temperature, equilibrium times up to
one hour are recommended.
Electrode Response
Plotting the electrode mV potential against the cyanide concentration on semi-logarithmic paper
results in a straight line with a slope of about 57 mV per decade.
The time needed to reach 99% of the stable electrode potential reading, the electrode response time,
varies from several seconds in highly concentrated solutions to several minutes near the detection
limit.
A drifting potential reading or a decrease in electrode slope may mean that the electrode membrane
needs polishing.
To polish the membrane:
1. If using polishing paper, cut off a 1-2" piece and place it face up on the lab bench.
2.
Put a few drops of distilled or deionized water in the center of the paper.
3.
Holding the paper (cotton) steady with one hand, bring the membrane of the electrode
down perpendicular to the paper and, with a slight swirling motion, gently polish the tip of
the electrode against the surface of the polishing paper (cotton) for a few seconds.
4.
Rinse the electrode surface with distilled or deionized water and soak the electrode tip in
standard solution for about five minutes before use.
5.
If using jeweller's rouge, place a cotton ball on the table top and flatten it using the bottom
of a beaker. Put 1-2 drops of distilled or deionized water in the center of the cotton pad.
6.
Add a small amount of jeweller's rouge to the damp cotton. Continue with Steps 3 and 4
above.
7.
Rinse the electrode surface with distilled water and soak the electrode tip in 1X10
-4
M or 1
ppm standard solution for about two minutes before use.