Approaches to eliminate elution solvent modifiers in the mixed-mode solid-phase extraction (SPE) of drug residues for on-line GCMS and LCMS analysis

Mixed mode SPE has been used successfully for the extraction of a variety of drugs from biofluids and specifically from urine. The primary elution and washing solvents and even the exhausted urine have been used in multi-eluate strategies. The need to use modifiers such as ammonia in the organic elution solvent limits the use of mixed-mode sorbents for on-line and rapid throughput analysis because the modifier must be removed or neutralised prior to chromatography. We describe a modification of the mixed-mode extraction of urine on C8/SCX type sorbents that allows the recovery of the basic fraction with modifier free solvents.