to the pH Theory Page.
The pH of a solution measures the degree of acidity or alkalinity
relative to the ionization of water.
Measuring pH involves comparing the potential of solutions with
unknown [H+] to a known reference potential. pH meters convert the
voltage ratio between a reference half-cell and a sensing half-cell to
pH 0 =
pH 4 =
pH 7 =
pH 10 =
pH 14 =
The voltage on the outer glass surface
changes proportionally to changes in [H+]. The pH meter detects the
change in potential and determines [H+] of the unknown by the Nernst
(2.303RT/nF) log(unknown [H+]/internal [H+])
E = total potential
difference (measured in mV)
Er = reference potential
R = gas constant
T = temperature in Kelvin
n = number of electrons
F = Faraday's constant
[H+] = hydrogen ion
electrode consists of two
half-cells; an indicating electrode and a reference electrode. Most
applications today use a combination electrode with both half-cells
in one body. Over 90% of pH measurement problems are related to the
improper use, storage or selection.
Since pH glass electrodes measure H+
concentration relative to their reference half-cells, they must be
calibrated periodically to ensure accurate, repeatable measurements.
Although calibration against one buffer typically ensures accurate
pH readings, frequent two-buffer calibrations ensure the most
reliable results. When selecting buffers, attempt to purchase
buffers on either side of your pH value you will be measuring.
When finished using your electrode,
you should always rinse it with DI water and blot the end dry with a
paper towel. Always store your electrode in storage solution to
ensure that your electrode glass stays hydrated. The storage
solution will also keep your reference wet and slow down the ion
exchange across the reference.
When cleaning your
please use a mild soap and warm water. Do not use HCl prior to soap
and water. Do not use abrasives on the pH glass.
that are commonly use of our electrodes:
- Calomel (Hg/Hg2Cl2) or Double junction
Waste water treatment
- Standard Ag/AgCl with
Flat or low sample
volumes - Flat glass electrode
Cheese or semi-solids
- Spear tip glass electrode