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Chemical Analyses: Water: Electrical Conductivity
The electrical conductance (EC) of a solution is a measure of the
ability of a solution to conduct a current. It is a property attributable
to the ions in solution. Electrical current is transported through
solutions via movement of ions, and conductivity increases as ion
concentration increases. The conductivity of a solution is measured
between two spatially fixed inert electrodes of known surface area.
Conductance is directly proportional to the electrode surface area
and inversely proportional to the distance between the electrodes.
In the international system of units, conductivity is reported as
decisiemens per meter (dS/m).
Conductivity can be used for a variety of applications at mine
sites, including:
- Comparing with other water quality parameters to show potential
gross errors in analysis. For example, an increase or decrease
in conductance of a particular water source will result in a similar
increase or decrease in other water quality parameters such as
total dissolved solids, sulfate, and metals. If this is not observed,
analysis should be considered suspect and repeated;
- Estimate the total dissolved solids in a sample by multiplying
conductivity by an empirical factor determined from analysis.
Conductivity results given alone are very limiting as they do not
measure individual contaminants nor the overall state of the water
(MEND,
2001).
The common method for measuring conductance is described in Standard
Methods, 1998, Section 2510. See below for a brief description
of the method.
Conductivity method description
The conductivity of a sample is measured with a self-contained conductivity
meter (Wheatstone bridge or equivalent). The instrument must be
standardized with KCl solutions of known conductance before use.
The cell is washed with 0.01 M KCl followed by one to two rinses
with the sample prior to measurement. Temperature corrections are
made if the sample is not analyzed at 25�C.
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