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Hanna Instruments HI931 - Page 109

Hanna Instruments HI931
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7-11
pH MODE
PREPARATION
Pour small quantities of the buffer solutions into clean beakers. If possible, use plastic beakers to minimize any EMC interferences.
For accurate calibration and to minimize cross-contamination, use two beakers for each buffer solution: one for rinsing the electrode
and one for calibration. If you are measuring in the acidic range, use pH 7.01 or 6.86 as the first buffer and pH 4.01/3.00 or 1.68
as the second buffer. If you are measuring in the alkaline range, use pH 7.01 or 6.86 as the first buffer and pH 10.01/9.18 or
12.45 as the second buffer.
For extended range measurements (acidic and alkaline), perform a five-point calibration by selecting five buffers across the entire pH
range.
CALIBRATION PROCEDURE
During calibration, the user has a choice of 8 standard buffers: (pH 1.68, 3.00, 4.01, 6.86, 7.01, 9.18, 10.01, 12.45) and up to 5
custom buffers.
For accurate measurements it is recommended to perform a five-point calibration. However, at least a two-point calibration is
suggested. For pH titrations, the selected buffers should bracket your end point (e.g.: if your end point value is at 8.5, use 7.01 or
6.86 and 9.18 or 10.01 for calibration).
To begin calibration:
Press . If the instrument was calibrated before the old calibration can be cleared by pressing .
Note: It is very important to clear calibration history when a new electrode is used.
Immerse the pH electrode and the temperature probe approximately 4 cm (1.5”) into a buffer solution and stir gently.
• If necessary, select the pH calibration buffer value with or .
Once the reading has stabilized press to update the calibration. The calibration buffer will be added to the Calibrated
Buffers section.
Rinse the pH electrode and the temperature probe, then immerse them into the next buffer solution and follow the above
procedure or press to exit the calibration.
Notes:
The new calibration points will replace old ones if the difference between them is ± 0.2 pH.
Buffers used in older calibrations will not have a solid background.
If calibrating with a standard buffer in MTC mode, the pH value and temperature can be modified by pressing . The
values can be adjusted using the numeric keys. Press to save the new values.

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