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4)After exposure to a sample, buffer or rinse solution,
shake the electrode with a snap motion to remove
residual drops of solution. This action will minimize
contamination from carryover.
5)As a rinse solution, use a part of the next sample or buffer
which is to be measured. This action also will minimize
contamination from carryover.
6)When calibrating, use a buffer close in value to that
expected from the sample. This action will minimize span
errors.
7)Keep buffers and samples at the same temperature. This
action will eliminate the need to correct values for
temperature effects.
8)pH readings stabilize faster in some solutions than others;
allow time for the reading to stabilize. In general, buffers
provide stable readings in several seconds (tris buffers
take somewhat longer) while samples usually take longer
times.
9)Keep in mind that all pH electrodes age with time. Aging
is characterized by shortened span and slower speed of
response. If the meter has a manual or microprocessor
slope (span) control, the control can be adjusted to
compensate for electrode span errors ( but will not effect
the speed of response ). Aging is best detected by
calibrating the electrode in, for example, 7 buffer, then
rinsing and placing the electrode in 4 buffer. As a rule, if
the span is 10 % or more in error (a reading of 4.3 or
higher for this example) the electrode should be cleaned and
retested (see the Electrode Cleaning Section) or
reconditioned ( see the Reconditioning Section ).
If performance is not restored the electrode should be
replaced.
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