Section 3: Method Performance Tests
- Before sample analysis, the laboratory must demonstrate the ability to achieve acceptable recoveries of native and surrogate PCDDs/PCDFs by conducting method performance tests as described in this section. These results must be documented, available for examination, and current (obtained within a 3-month period before sample processing begins). Three test samples of blank media, spiked with known amounts of native standards and labelled surrogates, should be prepared, extracted, and cleaned up according to normal procedures. Appropriate surrogate standard congeners and their spike levels for both LRMS and HRMS analysis are described in Section 4(i). The native congener spiking solution should contain all seventeen 2,3,7,8-substituted dioxin and furan congeners. Native congener spike levels should be selected to produce sample extract concentration levels equal to or near those of the appropriate (LRMS or HRMS) CS3 calibration standard solution (see Section 5).
- The performance test sample (e.g., filter, XAD, water, soil, ash) should be similar in size and nature to that of actual samples and either be free of target analytes or contain known trace levels of analytes that will not significantly affect the accuracy of native-congener spike recovery data.
- All surrogate recoveries for each of the three tests must be within the range of 40 to 120%.
- For each of the three tests, recovery for each of the native PCDD/PCDF congeners (corrected for surrogate recovery) must be within the range of 80 to 120% of the spiked value (i.e., accuracy of ± 20%).
- No samples should be processed until the method performance tests yield acceptable results. Tests must be repeated whenever extraction or cleanup procedures are modified; whenever there is a change in the lot number of chemicals used for cleanup; and whenever method performance test results are not current (within 3 months).