Thermo Fisher Scientific CyberScan pH 5000 - Manual (Page 124)

Instruction Manual CyberScan pH5500/ 5000
11.6 Analate Subtraction
The analate subtraction method is useful when no ion specific
electrode is available to measure the ion of interest directly. Like
known subtraction the sample and the standard contain different ionic
species. However, the ion being measured is in the standard and not
in the sample. The reduction of free ions in the standard solution is
proportional to the concentration of the ion of interest in the sample.
See ISE theory page 133.
To take a measurement
1. Immerse the ion selective electrode in a known volume of the
sample solution.
2. Stir the sample.
3. Touch AS to take the first mV reading of sample. Wait for the
reading to stabilize (STABLE will appear).
OR
Touch AS to accept the current reading.
4. Add a known volume of standard solution to the sample.
5. Touch AS to take the second mV reading of sample. Wait for the
reading to stabilize (STABLE will appear).
OR
Touch AS to accept the current reading.
6. Use the keypad to enter the sample volume.
7. Touch enter to accept the value.
8. Use the keypad to enter the standard volume.
9. Touch enter to accept the value.
119