The use of electron impact and positive chemical ionization mass spectrometry in the screening of beta blockers and their metabolites in human urine

Abstract

The use of several mass spectrometry technologies including electron impact (EI) and positive chemical ionization (CI) in both full-scan and multiple ion detection (MID) analysis for the urine analysis of several beta blockers and metabolites has been investigated. These drugs were extracted using an alkaline solid-phase extraction procedure and identified as their respective trimethylsilyl-trifluoroacetyl (TMS-TFA) derivatives on capillary gas chromatography/mass spectrometry. Isobutane proved to be the preferred reagent gas for the positive CI mass spectrometry of TMS-TFA derivatives of beta blockers, in comparison with others, such as methanol, ammonia and methane, since mass spectra with little fragmentation and abundant ions at high mass were obtained. By combining EI mass spectrometry and isobutane positive CI mass spectrometry using the ion trap detector, the identities of the main co-extracted metabolites were confirmed. Absolute detection limits were 0.15 ng for full-scan analysis (EI as well as positive CI mass spectrometry) and 0.08 ng for MID analysis (EI as well as CI mass spectrometry). The detection times of beta blockers in human urine were at least two- to three-fold the elimination half-life of these drugs. The analytical potential of the above mass spectrometric techniques has been discussed.