58
Glossary,
continued
Sensing half-cell—Provides a voltage proportional to the
concentration of a specific ion in solution.
Siemen—The unit of conductivity equivalent to mho (ohm
-1
).
Conductivity is often expressed as microSiemens per
centimeter (
µ
S/cm) and milliSiemens per centimeter (mS/cm)
and it is a measure of how readily a sample conducts electricity.
More concentrated solutions conduct more electricity and have
higher conductivity.
Sodium error (alkaline error)—Occurs in strongly alkaline
solutions, generally greater than 13 pH, when concentrations
of H
+
are low, and small, positively charged ions such as Na
+
generate potential differences across the pH glass membrane.
These differences can result in measurement errors between
-0.5 and -1.0 pH.
