Page 70 - Modern Analytical Chemistry

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Evaluating Analytical Data

A problem dictates the requirements we place on our
measurements and results. Regulatory agencies, for example, place
stringent requirements on the reliability of measurements and results
reported to them. This is the rationale for creating a protocol for
regulatory problems. Screening the products of an organic synthesis,
on the other hand, places fewer demands on the reliability of
measurements, allowing chemists to customize their procedures.
When designing and evaluating an analytical method, we usually
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make three separate considerations of experimental error. First, before
beginning an analysis, errors associated with each measurement are
evaluated to ensure that their cumulative effect will not limit the utility
of the analysis. Errors known or believed to affect the result can then be
minimized. Second, during the analysis the measurement process is
monitored, ensuring that it remains under control. Finally, at the end
of the analysis the quality of the measurements and the result are
evaluated and compared with the original design criteria. This chapter
is an introduction to the sources and evaluation of errors in analytical
measurements, the effect of measurement error on the result of an
analysis, and the statistical analysis of data.

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