Evaluation of the Analytical Procedure

A new experimental design for method evaluation was recently developed [18,24-27]. The method evaluation design recommends that at least 10 independent method runs should be performed on at least 10 different days. At each true concentration two method evaluation samples (ME samples) must be prepared, and the concentration of the analyte in the sample should be estimated on two different randomly selected days. For each run a new calibration graph should be prepared in the range of the method. The evaluation of the analytical method is obtained by a method evaluation plot (ME plot) showing the measured concentrations vs. the true concentrations (conventional true 

The method evaluation ensures that the experimental standard deviation (a) is a valid measure of the combined uncertainty and that the basic assumptions for the statistical tests for possible systematic errors are fulfilled. The systematic errors are zero point errors if a is significantly deviating from zero and proportional errors, if P is significantly deviating from 1 [6,19,26,28]. 

The square root of the relative mean square error (RMSE ) may be used for the simultaneous estimation of the uncertainty and systematic errors RMSE = [[(o/p + (P- l)f + (ay/p) ]. For lead in blood RMSE values are calculated and plotted vs. the true concentration (py) in Fig. 2. 

The limit of quantification, also denoted limit of determination, is the lowest limit for precise quantitative measurement, i.e., the relative uncertainty (8%) does not exceed a preselected 8 maximum % value. A value of 108i (equivalent to a 890 = 10%) has been suggested by lUPAC 

Plot of MEF for lead in blood estimated value of lead vs. the conventional true concentration. Intercept ot = 0.0526 slope P = 0.8483. 

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The final evaluation of the analytical procedure with generated filters resulted in a modified procedure which was "rugged" for the analysis of Be, Cd, Co, Cr, Cu, Mn, Mo, Ni, and Pb. The method was not ruggedized for Pd because the absence of perchloric acid from the developed procedure made it incompatible for Pd. 

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