Before switching the meter back to the NORM (normal) mode, make certain to reset the meter needle to
7.0. This prevents pegging the needle
For example, a solution has a starting pH of 3.25 and needs to be adjusted to an exact pH of 4.30 +.01.
A pH 4.00 buffer solution is a good reference point. The probe is placed in pH 4.00 buffer. Once in the
expanded mode, the meter needle is set at pH 10.00. Therefore in the expanded mode, the pH scale
would read as follows:
pH 0.0 is now equal to 3.00
pH 1.0 is now equal to 3.10
pH 3.0 is now equal to 3.30
pH 7.0 is now equal to 3.70
pH 10.0 is now equal to 4.00
pH 13.0 is now equal to 4.30
pH 14.0 is now equal to 4.40
Many electrode problems can be eliminated with reasonable care. Proper storage and use decreases down-time and
provides maximum benefits
Gel and refillable electrodes should be stored in an acidic solution with a low salt content.
Commercial soaking solutions are available or you can make your own by mixing a 1M KCI solution adjusted to pH 4.0.
Electrode storage in a field unit is more difficult due to the horizontal storage. To assure proper hydration of the
pH bulb, the electrode should always be stored wet in the solution described above. The easiest way to accomplish this is
to store the electrode using the plastic cap or soaking bottle that accompanies the new electrode when shipped.
Electrodes should always be used in a vertical position.
Electrodes should be rinsed between samples with distilled or deionized water. NEVER wipe an electrode to
remove excess water, just blot the end of the electrode with a lint free paper. Wiping an electrode can cause spurious
readings due to static charges.
The level of filling solution in refillable electrodes should be kept at least 2/3 full. The filling hole should be open
pH electrodes are fragile. A proper electrode holder should be used to provide support and aid in raising and
lowering the probe into solutions.