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Here are some more information for Millivolt Meter:

pH Buffer Calibration Verification

pH Buffer Calibration work requires calibration standards that are dependable and accurate to the specifications expected/listed. Providing your equipment is maintained well, measuring pH should not be a chore. Be sure you go through the meter checkout procedure for your meter according to manufacturer's directions. Also, perform a check on your electrode. To our surprise, a prominent brand of (high quality) electrodes did not include the electrode check out procedure in their owner's manual. But with a quick phone call, their tech person explained it to us. Electrode checks involve taking millivolt readings for the electrode when in buffers 7 and 4, then subtracting the difference, and checking that that figure falls within their parameters. Failure of the electrode will result in erratic readings, and drift.

Three point calibrations give the most accurate results. For less demanding work, 2 point is useful and quicker. Buffers sold in the lab market are traceable to NIST Standard Reference Material. We, in 2003, did some internal testing and found that of 3 brands obtained, not one was within the 0.1 pH unit tolerance guaranteed by the manufacturer, and total variation between the 3 was a staggering 0.5 units.

NIST Traceable means that the manufacturer is using these materials provided by NIST, drying the appropriate ones (some should not be dried), weighing them on a semi micro balance, and dissolving the salts in high purity, carbonate free water to volume. These prepared standards are then used to calibrate the meter, before measuring/testing the values of the buffers manufactured in house. This is repeated again for extra accuracy.

About the Author

Joseph E. Papa, Sr. Chemist
Exaxol Chemical Corporation
HemaFast Medical Stain System

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