Hanna Instruments HI931, User Manual, Page: 109 / 218

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.