pH meter
You can make your own ph pen probe storage solution (3 molar KCL)
with ph 4 buffer solution + potassium chloride.
Mix 1g potassium chloride (KCL) per 100ml ph buffer 4 solution to make
3 molar kcl storage solution. The gel dries out quickly if left in open
air or is stored in reverse osmosis or tap water leeches potassium
chloride ions as the probe tries to make equilibrium. Storing the probe
submerged in 3 molar kcl storage solution is best (better than few
drops in cap) for years of life out of the ph pen. Change the storage
solution every 2-3 months. Not a scientist or student but a
grower using common sense.
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Electrodes should always be stored in aqueous and ion-rich solutions.
This ensures that the pH-sensitive gel layer which forms on the pH
glass membrane remains hydrated and ion rich. This is necessary for the
pH membrane to react in a reliable way with respect to the pH value of
a sample. Short term storage: In between measurements or when the
electrode is not being used for brief periods of time, it is best to
keep the electrode in a holder containing its inner electrolyte
solution (e.g. 3 mol/L KCl), or in a pH 4 or pH 7 buffer. Ensure that
the level of solution in the beaker is below that of the filling
solution in the electrode. For long term storage: Keep the electrode
wetting cap filled with the inner electrolyte solution, pH buffer 4 or
0.1 mol/L HCl. Make sure that the filling port for reference and
combination electrodes is closed to avoid loss of the electrolyte
solution through evaporation, which can cause the formation of crystals
within the electrode and junction. Never store the electrode dry or in
distilled water as this will affect the pH-sensitive glass membrane and
thus shorten the lifetime of the electrode.