Direct HPLC analysis of ketoprofen in horse plasma applying an ADS-restricted access-phase

Making up part of the unique family of restricted access materials (RAM) the Lichrospher ADS (alkyl‐diol silica) sorbents have been developed as special packing materials for precolumns used for LC‐integrated sample processing of biofluids. The advantage of such phases consists of direct injection of untreated biological fluids without sample clean‐up and elimination of the protein matrix together with an on‐column enrichment. The plasma samples, with internal standard phenacetin added (not essential), were brought onto the precolumn (C‐18 ADS, 25 µm, 25 × 4 mm i.d.) using a phosphate buffer, 0.1 M, pH 7.0. After washing with the buffer, the ADS column was backflushed with the mobile phase phosphate buffer 0.05 M pH 7.0: acetonitrile (80:20), thus transporting the analytes onto a reversed‐phase column Ecocart 125‐3 HPLC cartridge with a LiChrocart 4–4 guard column, both packed with LiChrospher 5 µm 100 RP‐18; after separation detection was performed in UV at 260 nm. Essential features of the method include the novel precolumn packing, the absence of sample pretreatment, a quantitave recovery, good precision and accuracy, as well as a considerable reduction of analysis time compared to conventional manual methods applied in bioavailability studies. Copyright © 1999 John Wiley & Sons, Ltd.