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If the electrode is polluted by proteinaceous materials (such as blood), it
should stand in a pepsin solution overnight and then be cleaned before
use. The pH electrode wears away by being used. If the electrode tends to
respond slower and calibration becomes difficult, even after cleaning, it
should be replaced by a new one.
A pH measurement is always relative which makes it necessary to
calibrate regularly.
Zero point:
Each electrode has its own specific pH value, corresponding to the zero
potential point (ISO pH). This specific pH value can differ from its
theoretical zero point (e.g. 7 pH) by a few tenths of a pH.
Slope:
A good electrode follows the Nernst equation within 90 to 100 %. If the
slope lies outside these limits, the electrode becomes slow and may not
be optimal for most applications.
1.
Select the pH range by pressing MODE (see 'Channels' page 4). The
display will immediately show the measured pH according to the
previous standardisation. Should you want to restandardise, press
CAL.
2.
Rinse the electrodes with distilled water and immerse them in the first
buffer solution.
3.
The display shows one of the 9 buffers in memory (b1) or the manual
input (M1) of user specified buffers, e.g. [b1=4.01] while [b1] or [M1]
is blinking. Select the proper buffer with
wish to change the manual buffer, first press RES to reset to the
proper value with
4.
The instrument shows the measured buffer and will standardise
automatically when readings are stable ([=] stops blinking). If the
buffer has a different temperature, compensate the indicated value
manually with
5.
Go on in the same way with the next buffer (b2) and always press
CAL. Press MODE to start the measurements.
6.
After rinsing the electrodes with distilled water, immerse them in the
samples and read the pH-value from the display.
7.
Rinse the electrodes always with distilled water after use and store
them in a 3...4 M KCl solution.
∗ See page 66 for the buffers in memory.
∗ A blinking decimal point warns you for unstable measurements. Wait
to read the display!
∗ Stirring the solution during the measurements promotes the
homogeneity and is therefore always recommended.
∗ The instrument will refuse automatic standardisation when the
electrode is unstable. Insufficient stirring or a worn electrode may be
the cause. Select a lower resolution for a more rapid standardisation
or replace the electrode!
∗ Press RES to change the resolution from 0.1 to 0.01 pH.
or
and then press CAL.
or
(not necessary when using a Pt1000).
or
and press CAL. If you
pH
measurement
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