LaMotte COMBINATION pH ELECTRODE 1904 - Manual

COMBINATION pH ELECTRODE
CODE 1904
OPERATING TECHNIQUES
1.
The electrode is shipped in a plastic bottle containing a solution of potassium
chloride in buffer. The electrode should remain in the bottle until it is used. The
bottle and the solution should be saved for storing the electrode (see Electrode
Storage).
2. During shipment the air bubble in the electrode’s stem may move into the bulb
area. If bubbles are seen in the bulb area, hold the electrode by its top cap and
shake downwards.
3. Vigorously stir the electrode in the sample, buffer or rinse solution to bring
solution to the electrode’s surface quickly and improve speed of response.
4. Use a part of the next sample or buffer which is to be measured in the rinse
solution to minimize contamination from carryover.
5. When calibrating, use a buffer close in value to that expected from the sample to
minimize span errors.
6. Keep buffers and samples at the same temperature to eliminate the need to
correct values for temperature effects.
7. pH readings stabilize faster in some solutions than others; allow time for the
reading to stabilize. In general, buffers provide stable readings in several seconds
(tris buffers take somewhat longer) while samples usually take longer.
8. Keep in mind that all pH electrodes age with time. Aging is characterized by
shortened span and slower speed of response. If the meter has a manual or
microprocessor slope (span) control, the control can be adjusted to compensate
for electrode span errors (but will not affect the speed of the response). Aging is
best detected by calibrating the electrode in, for example, a 7 buffer, then rinsing
and placing the electrode in a 4 buffer. As a rule, if the span is 10% or more in
error (a reading of 4.3 or higher for this example) the electrode should be cleaned
and retested (see Electrode Cleaning). If performance is not restored, the
electrode should be replaced.