A general procedure was presented for the calculation of the limit of detection of an analytical process. The limit of detection was defined as the value corresponding to three standard deviations above the background response of the analytical instrument. Several problems associated with this method were pointed out. From the definition, it was not clear which standard deviation to use; the author notes that the ideal standard deviation, the standard deviation of instrument responses to blank samples, is not always easily available. Other potential problems were associated with nonlinear calibration curves and increasing instrument variability with increasing standard concentrations. The procedures for solving these problems were described. Calibration curves were determined from data sets composed of six to eight standards, replicated twice. Four types of calibration curves were used and linear, quadratic, and exponential equations were used to fit curves of increasing functions of response with increasing concentrations. For specific ion electrode analyses, the Nernst equation was used. The mathematical functions were described in detail. The author concludes that the methods are generally applicable and can be added to curve fitting programs.
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