Known Addition
Known addition is a convenient technique for measuring
samples because no calibration curve is required. It can be
used to verify the results of a direct calibration or to measure
the total concentration of an ion in the presence of a large
excess of a complexing agent. The sample potential is
measured before and after addition of a standard solution.
Accurate measurement requires that the following conditions
be met:
• Concentration should approximately double as a result of
the addition.
• Sample concentration should be known to within a factor
of three.
• In general, either no complexing agent or a large excess of
the complexing agent may be present.
• The ratio of the uncomplexed ion to complexed ion must not
be changed by addition of the standard.
• All samples and standards should be at the
same temperature.
16
Summary of Contents for 96-09
Page 7: ...4 ...
