Hach polymetron 9240 User Manual page 32

This process calculates the slope and offset of the ISE sodium electrode and the reference
electrode. It is based on the measurement of the potential and temperature of three different
samples, two of which contain known concentrations of sodium:
Measurement of a first sample of unknown concentration
•
Measurement of a second sample of known concentration
•
Measurement of a third sample of known concentration
•
The additions of known concentration are made to the overflow vessel which is partially emptied
to avoid any spillage. The volume of the overflow vessel has been factory defined during
preparation of the instrument. This parameter can only be modified by a qualified service
technician.
The sample to which the known additions will be made is measured. This measurement must be
stable and less than 1 per thousand of calibration solution concentration and becomes the
background point measurement P0 displayed on the analyzer.
The cycle is as follows:
1. Phase 1: The sample to which the known additions will be made is measured. This
measurement must be stable and less than 1 thousandth of the calibration solution
concentration. This becomes the background point measurement P0 displayed on the
analyzer.
2. Phase 2: The electrode is reactivated. This consists of injecting Sodium Nitrate into the
solution to maintain a high level of sodium measurement for a minimum of 5 minutes.
3. Phase 3: The measurement cell is rinsed. The overflow vessel is then refilled with fresh
sample.
4. Phase 4: The overflow vessel is drained slightly to allow enough room for the addition of the
first calibration solution.
5. Phase 5: The first calibration solution of known concentration is added and mixed with the
sample. The overflow vessel is drained into the measurement cell and the first concentration
measured and displayed as P1 on the analyzer.
6. Phase 6: The overflow vessel is rinsed and refilled with fresh sample.
7. Phase 7: The overflow vessel is drained slightly to allow enough room for the addition of the
second calibration solution.
8. Phase 8: The second calibration solution of known concentration is added and mixed with
the sample. The overflow vessel is drained into the measurement cell and the second
concentration measured and displayed as P2 on the analyzer.
9. Phase 9: The slope and offset are calculated and displayed. If the calculated slope and
offset values are within the acceptable limits they will be used for all future measurements.
Normal measurement is then resumed starting with a smart or fixed rinsing step.
Analyzer Overview
31