DETERMINATION OF BETA-AGONIST RESIDUES IN HUMAN PLASMA USING LIQUID-CHROMATOGRAPHY ATMOSPHERIC-PRESSURE CHEMICAL-IONIZATION MASS-SPECTROMETRY AND TANDEM MASS-SPECTROMETRY

A multi-residue gradient liquid chromatographic (LC) separation was de veloped for five beta-agonists (fenoterol, metaproterenol, terbutaline , salbutamol and clenbuterol) in human plasma and detection was made u sing LC/ atmospheric pressure chemical ionization mass spectrometry (L C/APCI-MS) in the selected-ion monitoring (SIM) mode. Detection limits for the protonated molecules of the beta-agonists were < 25 ppb in pl asma or 100 pg on-column and responses were highly linear over the ran ge 25-50 ppb. A solid-phase extraction (SPE) procedure, yielding recov eries of 67-104% from plasma spiked at 5 ppb with the five analytes, w as also developed. In-source collision-indnced dissociation was used t o produce mass spectra containing diagnostic fragment ions and a commo n mechanism of fragmentation for all the beta-agonists was identified. The LC/APCI-MS method was unable to determine salbutamol at levels < 10 ppb in spiked plasma. To determine whether this resulted from low S PE efficiency or matrix interference, LC/APCI-MS/MS was performed in t he multiple reaction monitoring (MRM) mode to enhance the selectivity of the analysis. The MRM results showed that high recoveries were obta ined for salbutamol, confirming the detrimental effect of co-eluting i nterferences in the LC/MS analysis. This study demonstrates the feasib ility of using SPE, gradient LC separation and highly sensitive/select ive detection using LC/APCI-MS and MS/MS for the multi-residue analysi s of beta-agonists at low ppb levels in a biological matrix.