LaMotte 1904 User 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.

CALIBRATION & MEASUREMENT

Follow the procedure recommended by the pH Meter manufacturer keeping in mind
the Operating Techniques outlined in the previous section. Frequency of calibration
is a function of the electrode, the pH meter and the solutions the electrode is exposed
to. The electrode and meter should always be calibrated together with the calibration
frequency determined by experience. Use two buffers, for example 7 and 4, or 7 and

10. Use the following procedure for both calibration in buffers and for sample

measurements:

1. Remove the electrode from the soaker bottle. Save the soaker bottle to store the
electrode in after use (see Electrode Storage).

2. Vigorously stir the electrode in a rinse solution. Shake off excess solution.

3. Vigorously stir the electrode in the buffer or sample, and then allow the electrode

to rest in the container.

4. Wait for the reading to stabilize. Record result.

5. Repeat these steps for each sample or buffer determination.

6. Between readings place the electrode in a beaker containing about 2 cm (1 inch)

of pH 4 buffer or distilled water.

ELECTRODE STORAGE

When pH readings are made several days or weeks apart, the electrode should be
stored by replacing it in the soaker bottle, filled with buffer solution.

ELECTRODE CLEANING

Coating of the pH bulb can lead to erroneous readings including shortened span. The
type of coating will determine the cleaning technique. Soft coatings can be removed
by vigorous stirring or by use of a squirt bottle. Organic chemical or hard coatings
should be chemically removed. Only in extreme cases should the bulb be
mechanically cleaned as abrasion can lead to permanent damage.

LaMOTTE COMPANY

Helping People Solve Analytical Challenges

PO Box 329 • Chestertown • Maryland • 21620 • USA

800-344-3100 • 410-778-3100 (Outside U.S.A.) • Fax [phone]

Visit us on the web at www.lamotte.com

®

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