Gerhardt VAPODEST 50 - Calibration; Calibration Performance

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C. Gerhardt GmbH & Co. KG
8. Calibration
In order to reach a perfect pH measurement the electrode has to be calibrated at regular intervals. A
two-point calibration is carried out. The zero point deviation is determined with the buffer solution pH
7, the slope with buffer solution pH 4 or pH 9. The selection of the second buffer solution depends on
the pH range to be worked with.
For Kjeldahl analysis the buffer solution pH 4 should be used. The measurements are displayed in
mV. The values are ideal if you get a zero point deviation of 0 mV and a slope of 58,2 mV/pH. The
tolerance for the zero point deviation should not exceed +/- 15 mV, the slope is acceptable between
50 mV and 70 mV/pH. The conversion of mV/pH is carried out after the calibration is completed.
During the measuring the actual voltage is shown. The ideal value for the buffer solution pH 4 is
174,6 mV if the zero point is exactly at 0 mV. A further criteria for the condition of the electrode is the
response time. If the electrode reacts slowly and does not give a stable measurement within 30s, the
calibration is not accepted. If one of the tolerance ranges is exceeded during the calibration, the
appropriate error message appears and the calibration must be repeated with a fresh buffer solution
and/or a new electrode. The last accepted calibration is the one stored. Although, in case the cali-
bration procedure did not succeed, the equipment would be ready for operation even though the
result would be wrong. Therefore, analysis should not be run, as the condition of the electrode is
crucial for the precision of the titration. For maintenance and storage of the electrode see the
manufacturer’s instruction. Buffer solutions should be kept at room temperature (20° C).
Attention:
Our experience has shown that the electrodes have an average life span of 1.5 - 2 years. in any
case, when measuring seems to become sluggish then make sure to exchange the electrode under
all circumstances. In order to guarantee a perfectly working instrument you should only use the
original electrodes from Gerhardt.
Select buffer solutions.
The electrode, rinsed with distilled water and dried
(dabbed, not rubbed!) is dipped into buffer soluti-
on pH 7. Start the measurement by pressing the
"Enter" key.
8.1. Calibration performance
1. Choose the "Calibration" key.
2.
3.
CALIBRATION