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Section No. 9.0 <br /> Revision No. 6 <br /> Date 6/1/88 <br /> Page 19 <br /> r <br /> 2. Analysis of Duplicates <br /> The preferred method of duplication at the laboratory is the <br /> analysis of a duplicate spike sample. A sample is chosen <br /> randomly, divided into equal aliquots, spiked with a known <br /> amount of the analyte and prepared for analysis. Duplicate <br /> samples are analyzed to determine the precision of the <br /> preparation and analytical techniques. Daily, the relative <br /> percent difference (RPD) between the spike and duplicate spike <br /> are plotted an control charts (see Attachment XI) . Relative <br /> percent difference is calculated as: <br /> T <br /> Amount in Spike I - Amount in Spike 2 <br /> RPD = --------•------------------------------ x 100 <br /> Spike i + Spike 2 <br /> ----------------- <br /> } 2 <br /> 3. Analysis bf Spiked Samples <br /> In order to assure the accuracy of the analytical procedure, a <br /> sample is randomly chosen and spiked with a known amount of the <br /> analyte to be tested. The increased value for a spiked sample <br /> resulting from the addition of the analyte at a known <br /> concentration compared to the value obtained 'for that same <br /> analyte in the unspiked sample determines the percent recovery. <br /> Daily, data are plotted on control charts that are maintained <br /> as matrix specific and analyte specific charts (see Appendix). <br /> The percent recovery for a spike sample is calculated as <br /> follows: <br /> Amt. found in Spiked Sample - Amt. Found in Sample <br /> Rec.= •--------------------------------------------------- X100 <br /> Known Amount Added <br /> ir; �. <br />