On-line coupling of automated solid-phase extraction with high-performanceliquid chromatography and electrochemical detection - Quantitation of oxidizable drugs of abuse and their metabolites in plasma and urine

The concentration effect of automated on-line solid-phase extraction (SPE) in combination with HPLC and very sensitive electrochemical detection was e mployed for the determination of N-ethyl-4-hydroxy-3-methoxy-amphetamine (H MEA, the main metabolite of the ecstasy analogue MDE), Delta(9)-tetrahydroc annabinol (THC) and 11 -nor-Delta(9)-tetrahydrocannabinol-carboxylic acid ( THC-COOH) in plasma and urine in comparison to a previously published psilo cin assay. For the SPE either CBA (functional group: carboxypropyl)- or CH (functional group: cyclohexyl)-sorbent was used. The following separation w as carried out on a reversed-phase column (LiChroCart, Superspher 60 RP sel ect B from Merck). Depending on the hydrodynamic voltammogram of the analyz ed substance the oxidation potential varied from 920 mV up to 1.2 V. In spi te of using high potentials, precision and accuracy were always within the accepted statistical requirements. The limits of quantitation were between 5 ng/ml (THC, THC-COOH in plasma) and 20 ng/ml (HMEA in plasma). Advantages of on-line SPE in comparison with off-line methods were less manual effort , evidently smaller volumes (less than or equal to 400 mu l) of plasma or u rine and almost always higher recovery rates (>93%). The assays have been s uccessfully proven with real biological samples and found suitable for use in routine analysis. (C) 1999 Elsevier Science B.V. All rights reserved.