JANUARY 31 2003
Temperature also affects the potential of the reference cell. There is an
increase of approximately 0.9 mV per degree Celsius (0.5 mV per degree Fahrenheit),
so a measurement of -0.85 at 21 C (70 F) would read -0.835 at 4 C (40 F), and -
0.865 at 38 C (100 F).
To determine the accuracy of a reference electrode, multiple reference
electrodes must be used. In practice, there should be one reference electrode
maintained properly, which is not used in the field, to check other reference electrodes
against before they are used in the field. This "reference" reference electrode must be
properly initiated and stored.
Initiation of a Reference Electrode. The copper/copper sulfate reference
electrode must be properly cleaned and initiated to ensure accuracy. Improper cleaning
or initiation can cause significant changes in the potential of the reference (and
subsequent errors in all measurements taken). The metal electrode must be cleaned
properly and the electrolyte solution must be prepared properly to ensure accuracy.
Figure 7-1. Copper/Copper Sulfate Reference Electrode (Half-Cell)
CONE OR PLUG
Cleaning. Clean the metallic electrode thoroughly using nonmetallic
materials: Do not use metallic sandpaper, grinders, emery cloth, wire
brushes, knife blades, or any other metallic cleaning method. For
example, aluminum oxide sandpaper will deposit particles of aluminum on
the copper, or wire brushes will deposit particles of steel on the copper,
thus changing the potential of the electrode. The proper way to clean the
copper rod is with non-metallic sandpaper, such as flint paper, and a cloth.
All of the copper oxide (green color) must be removed from the electrode,
and it should be clean and shiny (no pitting). If the electrode is pitted, the