Analysis of drugs of abuse in human plasma using microextraction by packed sorbents and ultra-high-performance liquid chromatography

- Extraction of psychoactive substances by MEPS.
- Rapid determination of new drugs of abuse in plasma by UPLC-PDA.
- Low LOD and LOQ are achieved with this new method.
- Successful comparison of results obtained by MEPS-UPLC-PDA and SPE-GC-MS.

A miniaturized and simple method based on digitally programmed microextraction by packed sorbent (eVol®-MEPS) coupled to ultra-performance liquid chromatography (UPLC) has been developed for quantitative determination of three synthetic cathinones and seven conventional drugs of abuse and metabolites. The influence of several extraction parameters, such as washing and elution solvents were tested. In addition important variables affecting MEPS performance, namely sample volume, sorbent drying time, washing solvent volume, elution volume, number of extraction cycles, sorbent phase and pH, were evaluated using an asymmetrical screening design. The optimal experimental conditions involved 300 μL of plasma, loading 10 × 100 μL of sample through a C8/SCX sorbent in a MEPS syringe placed in the semi-automatic eVol® system, washing using 150 μL H2O:MeOH (90:10, v/v), drying for 0.5 min and elution using 200 μL dichloromethane:2-propanol:ammonium hydroxide (78:20:2, v/v/v). The drugs separation was achieved using an ACQUITY BEH Shield RP18 column (2.1 mm × 100 mm × 1.7 μm) in 3 min. Under optimized conditions the proposed method was validated in terms of selectivity, linearity, limits of detection (LOD) and quantitation (LOQ), precision and matrix effect, using standard addition calibration. The combination of MEPS and UPLC provides a method for the primary screening of the analytes in 18 min with excellent recoveries at three concentration levels, ranging between 80 and 104% (relative standard deviation <11%). The developed methodology has been successfully applied to plasma samples from polydrug abusers.