In the framework of wider exploration of the application of dried blood spots (DBS) in bioanalysis, by the DBS consortium of the European Bioanalytical Forum, one team of five laboratories investigated the merits of the various ways of IS addition prior to LC–MS/MS analysis. A set of 22 pharmaceutical compounds with log P in the range of 0–10 was selected for this purpose. Assessments were made of precision, recovery, and of the effects of prolonged storage.Results:
Assay precision was not significantly different for 3 month-aged samples as compared with ‘fresh’ samples stored for 7–22 days. Extraction recovery from 3 month-aged spots decreased for some of the analytes; the most widely employed addition of IS in the extraction solvent does not compensate for recovery in such cases.Conclusion:
From the overall results, it is clear that there is no ‘one size fits all’ approach to IS addition in DBS bioanalysis.