Solid-phase microextraction- probe electrospray ionization devices for screening and quantitating drugs of abuse in small amounts of biofluids

Probe electrospray ionization (PESI) is an ambient ionization mass spectrometry technique (AIMS) that is primarily used in qualitative studies, though researchers have recently combined it with sample preparation for the quantitative analysis of various analytes in biological matrices. This study presents a method that integrates solid-phase microextraction with PESI for direct coupling to a triple quadrupole mass spectrometer, and examines its ability to quantitate drugs of abuse. Intra- and inter-probe reproducibility experiments were conducted to assess the stability and reproducibility of the extraction-phase-coated PESI probes (coating length: 2 mm; coating thickness: 6.5 mu m). This research is the first documented instance wherein highly sensitive determinations were successfully attained using these microextraction and micro-desorption techniques in conjunction with small volumes of sample and extraction phase. A mixture consisting of IPA/H2O (1/1 v/v) + 0.1% FA was determined to be the optimal desorption solvent for SPME-PESI-MS/MS, as it facilitated high analyte enrichment in a picolitre of the solvent, which acted at the same time as efficient electrospray media. Furthermore, a method of quantifying drugs of abuse in 30 mu L of plasma without matrix modification was also developed. This method had an intra-day accuracy within the 80-120% range for all eight drugs of abuse at concentrations of 3, 30, and 90 pg mu L-1; the exception to this result was lorazepam at 30 pg mu L-1, which had an intra-day accuracy of 122%. The lower limit of quantification (LLOQ) for fentanyl and nordiazepam was pg mu L-1; the LLOQ for buprenorphine, codeine, diazepam, lorazepam, and propranolol was 5 pg mu L-1; and the LLOQ of oxazepam was 10 pg mu L-1.

Automated summary

Probe electrospray ionization (PESI) has been successfully integrated with solid-phase microextraction for highly sensitive quantitation of drugs of abuse. The optimal desorption solvent for SPME-PESI-MS/MS was determined, and a method for quantifying drugs of abuse in small volumes of plasma without matrix modification was developed. Intra-day accuracy for eight drugs of abuse was within acceptable ranges, with some exceptions noted for specific compounds.