MICRO LIQUID-CHROMATOGRAPHY MASS-SPECTROMETRY WITH DIRECT LIQUID INTRODUCTION USED FOR SEPARATION AND QUANTITATION OF ALL-TRANS-RETINOIC AND 13-CIS-RETINOIC ACIDS AND THEIR 4-OXO METABOLITES IN HUMAN PLASMA

The separation and quantitation of the pentafluorobenzyl derivatives of all-trans- and 13-cis-retinoic acids and their 4-oxo metabolites in human plasma on micro high-performance liquid chromatographic columns (0.32 mm I.D.) is described. The column outlet was directly coupled to the source of a quadrupole mass spectrometer via a simple SFC-frit interface. Negative ion chemical ionization conditions were obtained by coaxial introduction of ammonia as a reagent gas. A signal-to-noise ratio well above 3 was obtained for 1 pg of each analyte injected. The limit of quantitation calculated from spiked biological plasma extracts was 0.3 ng/ml.