Ambika,
Industry practice is to maintain usage logs for all
equipment that must be calibrated or otherwise maintained. Impact on the
product, rather than cost or size of the equipment, determine whether the
equipment is "major".
Yes, there must be a usage log for a pH meter and probe used in
production. The log must record in GMP fashion what batches the equipment
was used for. It should also record, or reference another recording
document, each standardization of the pH meter, including the batch
identification of each standardization buffer solutions used. (Your SOP
should guide on the pH's of the buffers used, which generally should
bracket the target pH range. Your SOP should also guide on what the
acceptable performance of the pH probe is, which is usually the slope of
the response.) The actual performance of the probe during
standardization, and that it passed or did not, are also to be recorded
in the usage log.
Frank Bales, Ph.D.
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