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Section No: 11 Revision No: 2.0 IR Date: January 15, 1994 Page: 3 of 18 Internal Quality Control 11.1.3.3 Surrogate Spikes Surrogate spikes serve as a check on the extraction process where extraction is a necessary part of the analytical procedure. When surrogate recovery is witWm limits it indicates that the extraction was complete. A surrogate is a compound not expected to occur in an environmental sample but has chemical behavior similar to that of the target analytes. EPA protocol requires surrogate spikes for specific ods on a per sample basis (including QCsamples). Initially method specific acceptance criteria are used. Eventually, or when method specific criteria are unavailable, the recoveries are control charted to obtain acceptance limits. 11.1.3.4 Matrix Spike/Matrix Spike Duplicates D The MS/MSD is used to verify matrix specific precision and accuracy. protocol normally requires analysis of MS/MSD samples for each analyti batch or matrix type. The MS/MSD spikes are manufacturer or laborato prepared from suitable reference standards. This standard may or may not ra yt ot independent 1.thecalibration stock The matrix/ recovery .:: 1, relative percent difference 1 acceptance +shown Section When matrixspikeoutsidelimitspublished 1respective 1 i` + {;LCS , i; method r:.control. If spikerecoveries outside i limitsdue 1': matrix :: 1 problems, 1 / + 1 1 •:reported 1 . interference. The spike recovery and RPD acceptance limits are test specific a are control 1 Y Duplicates Duplicates , ,; 1verifymatrix specificprecision. EPA 1 s'. 1 1 normally Y. _' requires analysis of duplicate samples for each analytical batch or matrix type. The relative percent difference (RPD) calculated from duplicate analyses provide an assessment �1 precision. The RPD Y r: t limits test specificandare control charted. 11.1.4.1 Efficiency vs. Dissolved Solids Chart Dissolved solids mask or decrease the radiation picked up by the counting wire. For each instrument an efficiency vs. solids chart must be generated as part of the initial demonstration of capability. In addition, whenever an instrument is maintained or repaired (i.e. a counting wire replaced) a new efficiency vs. solids charge must be generated. Samples containing solids such that the efficiency of counting drops below ten percent must be reset using a smaller aliquot so that the solids give acceptable counting efficiency. Prior to setting up a sample, an electrical conductivity measurement must be made for estimation of total dissolved solids. 11.1.4.2 Background Background samples are run daily, prior to sample analysis. however, a weekly average may be used for calculation purposes.