Extract and Re-Injection Stability

Once the extraction-clean-np steps have been completed the stability of the analyte in the analytical extract must be validated, both with respect to long term storage if the final analytical step can not he condncted immediately and also with regard to stahUity while the extract is sitting for some time in a vial in an antosampler waiting to he analyzed as part of a multi-sample run. 

Analyte stability in processed extracts for re-injection is assessed by analysis of stored QC sample extracts (minimum of low, mid and high QC samples, N 3) and comparison of these results to nominal concentration. The mean accuracy value for a set of stability QC extract samples should be within 15% of the nominal concentration values. The stability of the analyte in reconstituted extracts should be determined by analyzing a set of QC sample extracts that have been stored at room temperature (or under other conditions consistent with storage at the autosampler). Extract stabihty is measured by at least one of the following four procedures  

QC samples are prepared and injected together with calibrators to estabhsh a calibration curve the QC set is then re-injected. The re-injected QC samples are qnantified against the same calibration curve used for the initial injections ( Original Curve ). The period of re-injection is calculated from the time the last calibration standard was analyzed in the original analysis set to the time of the first re-injection of the QC samples. This experiment assesses the ability to reinject samples after completion of an analytical run without the need for re-injecting an entire set of calibration curve and QC samples. 

QC samples are prepared and injected together with calibrators to establish a cahbration curve as in 1.  

QC samples are extracted, stored at the appropriate temperature, and analyzed against a freshly prepared calibration curve with analytical QC samples. (Stored QC samples from a previously analyzed set may also be used for assessing extract stability.) The storage time is calculated from the time the final extracts were prepared to the time the first of these stability QC samples was injected. If extract stability is established with this experiment alone, then the requirement for re-injecting an entire set of calibration curve and QC samples applies. 

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