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' SOP TO-14A/15 <br /> Rev 4 <br /> December 2007 <br /> ' (1) Estimate the MDL using one of the following: <br /> a) The concentration value that corresponds to an instrument signal/noise <br /> ratio in the range of 2.5 to 5, or <br /> ' b) The concentration equivalent of 3 times the standard deviation of <br /> replicate measurement of the analyte in helium or zero air, or <br /> C) The region of the standard curve where there is a significant change in <br /> ' sensitivity (i.e., a break in the slope of the standard curve). <br /> (2) Prepare (i.e., extract, digest, etc.)and analyze seven samples of 50 cc vapor <br /> ' containing the analyte of interest at a concentration three to five times the <br /> estimated MDL. <br /> ' (3) r Determinethevariance (S2) for each analyte as follows: <br /> ' n 1 I[�(x, —x)2 J <br /> S2 = _ <br /> ' where xi =the ith measurement of the variable x and x =the average value of <br /> x <br /> X— 1Y'x, <br /> n ;_, <br /> ' (4) Determine the standard deviation (s) for each analyte as follows: <br /> s= (S2)1/2 <br /> ' (5) Determine the MDL for each analyte as follows: <br /> ' MDL=3.14(s) <br /> (note: 3.14 is the one-sided t-statistic at the 99 percent confidence level <br /> appropriate for determining the MDL using 7 samples) <br /> ' (6) If the spike level used in step 2 is more than 5 times the calculated MDL, <br /> repeat the process using a smaller spiking level. <br /> ' Where multiple instruments are used, the MDL used for reporting purposes <br /> shall represent the least sensitive instrument. <br /> ' 16.3.2 Estimated Quantitation Limit(EQL)formerly called Practical Quantitation limit <br /> (PQL)• <br /> Page 21 0£ 24 <br />