Should quantitation for Method 8260B (or Method 8270C) be done using the average response factor (RF) from the initial calibration or using an updated RF from the daily calibration check sample?
For SW-846 methods involving quantitative analyses, the average RF from the initial calibration should be used for quantitation. The daily calibration check standard is used for calibration verification, and it is fundamentally different from the approach called “continuing calibration” in the CLP organic Statement of Work (SOW) and some other programs. Use of the “continuing calibration” approach amounts to a daily single-point calibration and is not appropriate nor permitted in SW-846 chromatographic procedures for trace environmental analyses. Section 7.6.2.2 of Method 8260B and Section 7.7 of Method 8000B contain the language that clarifies EPA’s intent on this issue. There are a few screening procedures for organics in SW-846 that do utilize a single-point calibration for quantitation. However, these are clearly identified as screening procedures rather than truly quantitative methods.
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