Comparison of Liquid/Liquid and Solid-Phase Extraction for Alkaline Drugs

Abstract

The extraction of drugs from biological matrices is an essential specimen preparation step in current forensic postmortem laboratories. Traditionally, liquid/liquid extractions (LLE) were developed and employed to screen for the general unknown. However, solid-phase extractions (SPE) are becoming more popular as the availability of columns with suitable stationary phases increased. The purpose of this work was to determine if switching from an existing LLE to SPE was feasible. The limits of detection (LOD) for 122 drugs and metabolites were determined in blood following SPE and compared to previously determined LOD's by LLE, if available. There were 41 drugs that had LOD's in blood established by both methods; LLE had a lower LOD for 8 drugs (19.5%), SPE had a lower LOD for 16 (39%), and the LOD's were comparable in the remaining drugs. Although SPE cartridges were more expensive than LLE, SPE was determined to be a faster technique and doubled the number of specimens that could be extracted by one analyst within a specific timeframe. The SPE method utilized enabled the detection of several drugs not detectable after LLE (most notably, morphine and benzoylecgonine) and allowed the extraction of weakly acidic and neutral drugs with only one extra step.