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1 <br /> <br />j 8.2.2 In most cases, matrix spike levels should be .added at a <br />concentration equivalent to the corresponding regulatory level. If the <br /> analyte concentration is less than one half the regulatory level, the <br /> spike concentration may be as low as one half of the analyte <br /> concentration, but may not be less than five times the method detection <br /> limit. In order to avoid differences in matrix effects, the matrix spikes <br /> must be added to the same nominal volume of 1312 extract as that. which was <br />t analyzed for the unspiked sample. . <br /> 8.2.3 The purpose of the matrix spike is to monitor the <br />~, performance of the analytical methods used, and to determine whether <br />' <br />F' matrix interferences exist. Use of other internal calibration methods, <br /> modification of the analytical methods, or use of alternate analytical <br />' methods may be needed to accurately measure the analyte concentration in <br />the 1312 extract when the recovery of the matrix spike is below the <br /> expected analytical method performance. <br />' 8.2.4 Matrix spike recoveries are calculated by the following <br /> formula: <br />' %R (Y Recovery) = 100 (X$ - X~j / K <br />where: <br />' X =measured value for the spiked sample <br />XS = measured value for the unspiked sample, and <br />K" = known value of the spike in the sample. <br />~~ 8.2.5 Measured values are corrected for analytical bias using the <br />following formula: <br />' X~ = 100 (X~ / %R) <br />where: <br />' X~ = corrected value, and <br />X~ = measured value of the unspiked sample. <br />' 8.3 All Quality control measures described in the appropriate analytical <br />methods shall be followed. <br />' 8.4 Samples must undergo 1312 extraction within the following time <br />periods: <br /> <br /> <br />1 <br /> <br />1312 - 19 <br />Revision 0 <br />November 1990 <br />