Crucial importance of evaluating internal standards (IS) response and troubleshooting in effective LCMS method development, validation and sample analysis

Internal standards (IS) are commonly used in chromatographic analytical methods to correct for variability in sample processing and analysis. To achieve this, a constant amount of IS is added to all samples – except for a double blank in a batch – including calibration standards (CALS), quality controls (QCs), and subject samples prior to the initiation of extraction procedures.Therefore, by design, the responses of IS from all samples in an analytical run are anticipated to be similar to each other. However, in some instances, we observe variability in IS responses, even among samples processed and analyzed concurrently. It is worthwhile...