Page 99 - The Veterinary Laboratory and Field Manual 3rd Edition

68 Willy Schauwers

Figure 2.32 pH meter. Photo: Willy Schauwers, Provincial Institute for Hygiene, Antwerp, Belgium.

Each time the pH meter is used (or at least • Take care that the tip does not become covered
once every day) it should be ‘standardized’ with with a layer of protein or lipids (for example,
a solution of a known pH. Thereafter solutions from media). If this does occur, protein can be
of unknown pH can be measured. removed using 0.1% pepsin or 0.1 N HCl and
Two SOPs for pH-meters can be found lipids can be removed using acetone.
in ‘SOP-LABORATORY-EQUIP-02 pH-mV- • If possible, adjust the pH meter to the tem-
Temperature Meter Jenway 3510’ and ‘SOP- perature of the solution under test.
LABORATORY-EQUIP-03 pH-Conductivity- • Allow the pH meter to warm up for a few
TDS-Salinity-Temperature Meter’. minutes and ‘settle’ before taking a reading.
• When not in use, keep the electrode immersed
GuIdELInES For uSE in liquid.
Some general rules must be followed to ensure • Make sure that the solutions used to stan-
reliable results. dardize the pH meter are pure, that is, no
turbidity or dirt.
• Take great care of the sensitive and fragile tip • The date when the standard solution was
(bulb) of the electrode. Rinse it carefully in prepared should be noted so that it can be
distilled water before and after it is used and replaced with fresh solution if necessary (for
do not handle it roughly. example, monthly).
• Do not wipe the bulb but carefully absorb any • Maintain the correct level of potassium
hanging drops with tissue paper. chloride inside the electrode.

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