Thermo Fisher Scientific Ion Selective Electrodes Silver - Manual (Page 19)

Instruction Manual Silver/Silver Sulfide Electrode
19
50 32.1 64.1
If changes in temperature occur, the electrodes should be re-calibrated. The temperature range for
Eutech Silver/Sulfide Ion Combination Electrode is 0o-80oC, 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 silver concentration on semi-logarithmic paper
results in a straight line with a slope of about 57 mV per decade. (Refer to Figure 2.) The sulfide ion
also gives a straight line when the electrode mV potential is plotted against the sulfide
concentration, but the slope is about 26 mV per decade. (See Figure 1.)
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. (Refer to Figure 5.)
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.