Interpreting Calibration Curves
This depends on the chemical composition and temperature of the samples that are measured
regularly and can strongly affect how the efficacy of the electrode slope declines due to
aging of the electrode’s glass membrane. This information therefore provides clues that have
to be interpreted taking into account the true situation.
Situation Cause: Measure
Virtually constant The electrode has hardly The calibration interval can be
calibration results been subjected to increased.
over all four logged the effects of aging.
calibrations.
A constant Normal aging process Possibly shorten the calibration
reduction in slope of electrode. interval to always measure with
or zero point drift. current data.
A constant and Aging of the electrode Adhere to shorter calibration
strong reduction in slope can be accelerated by intervals to always measure with
and/or zero point drift in extremely acidic/basic current data. If the lifetime of
one direction. samples and/or the electrode is too short:
high temperatures. If appropriate, check whether the
electrode is suited for the samples
to be measured and the
measuring conditions.
An abruptly sharp Impure electrolyte, Replace electrolyte, clean
drop in slope compared to dirty membrane membrane (see electrode
last calibration or defective electrode. operation manual),
replace electrode
Strong fluctuations Measuring conditions If required, use special for
among calibration often vary greatly electrodes different measuring
results without (e.g. very hot or conditions (see also electrode
any identifiable trend. very acidic/alkaline operation manual).
media to be measured.
Strong fluctuations Fiber junction clogged Clean the electrode
in the zero point without (see electrode operation manual)
any identifiable trend If required, check whether the
electrode type used is suitable
for the sample.
After a constant Previous calibration Recalibrate because previous
reduction in slope, was incorrect. calibration was incorrect.
an increase occurs Cleaning or regeneration Document cleaning/
improved the performance regeneration.
of the electrode.
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