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VII VII VII VII VII. General Guidelines
General Guidelines
General Guidelines
General Guidelines
General Guidelines
Concentrated samples (>0.10 M) should be diluted
before measurement. Multiply the final result by the
corresponding dilution factor.
Calibration standards and sample solutions should
have the same ionic strength.
For high ionic strength samples, use standard addi-
tion or titration methods.
Calibration standards and sample solutions should
be at same temperature.
The magnetic stirrer may generate heat. Thermally
insulate beaker containing standard or sample from
magnetic stirrer by placing cork or other insulative
sheet between beaker and stirrer plate.
Calibration standards and sample solutions should
be stirred at the same rate using identical sized TFE
coated stir bars.
Rinse electrode pair with distilled or deionized water
between samples and gently dab dry with soft dis-
posable absorbent toweling. Do not rub electrodes.
Avoid Cd(OH)
precipitation or hydrogen ion interfer-
2
ence by maintaining pH of samples between 4.5 and
7.5 pH. Use Nitric acid or sodium hydroxide to adjust
pH.
Presoaking the cadmium sensor tip in a dilute stan-
dard will optimize response. Use concentrations ap-
-3
proximately10
M.
Presoaking the cadmium tip in a mild reducing solu-
tion such as ascorbic acid for a few minutes may be
helpful when oxidation of the membrane surface is
an issue between sample measurments.
A scratched, pitted, or oxidized pellet surface can cause
drift, a loss of low level response, or poor repeatability.
Optimum response can be restored by removing the
damaged surface with the microabrasive strip HI 4000-
70. Use gloves to protect skin. Cadmium dust is toxic.
Avoid large changes in temperature (thermal shock)
as it may damage the sensor.
6
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