SELECTIVE EXTRACTION OF BETA-BLOCKERS FROM BIOLOGICAL-FLUIDS BY COLUMN-SWITCHING HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY USING AN INTERNAL-SURFACE PHENYLBORONIC ACID PRECOLUMN

A column-switching HPLC method using an internal-surface phenylboronic acid precolumn for the selective extraction of beta-blockers from bio logical fluids has been developed. Filtered urine and plasma samples ( 50 mu l) were injected onto the precolumn equilibrated with methanol-0 .05 M disodium hydrogenphosphate (5:95, v/v). After the precolumn had been washed briefly, the selectively retained beta-blockers were elute d with methanol-0.05 M phosphate buffer (pH 2.0) and transferred to a reversed-phase analytical column, on which they were then separated. E ven after exposure to at least 160 injections of non-treated urine and plasma samples, the retention efficiency of the precolumn was maintai ned with no increase in back pressure. Quantitative recoveries and goo d reproducibility were demonstrated with pindolol.