Page 59 - Pharmaceutical Analytical Chemistry II - Pharm D Clinical- 07-PA202

Calibration of pH meter

Calibration should be performed at the beginning of each day. The
reason for this is that the glass electrode does not give a
reproducible e.m.f. over longer periods of time. Calibration should be
performed with at least two standard buffer solutions that span the
range of pH values to be measured. For general purposes buffers at
pH 4.01 and pH 10.00 are acceptable. The pH meter has one control
(calibrate) to set the meter reading equal to the value of the first
standard buffer and a second control which is used to adjust the
meter reading to the value of the second buffer. Standard buffer
sachets can be obtained from a variety of suppliers.

Steps of pH measurement

1. Sample to be measured can be collected in any glass or plastic
container. Put enough sample so that you can submerge the tip
of the electrode. Place the electrode in the sample and wait for
the meter to equilibrate (the signal becomes steady) .

2.Read the pH directly from the meter

Cleaning the pH meter electrode:

After each single measurement, the electrode is rinsed
with distilled water or deionized water to remove any traces of the
solution being measured, blotted with a wipe to absorb any
remaining water which could dilute the sample and thus alter the
reading, and then quickly immersed in another solution.

Storage of the pH electrode when not in use.

The pH electrode bulb needs to be moist at all times. When you
are done with the electrode pour electrode storage solution into the
cap that comes with the electrode and put the cap over the bulb of
the electrode. Keep the cap on until next use. If the electrode is
being stored for a long time you may want to check the cap to be
sure the storage solution is still in the cap and keeping the bulb
moist.

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