Application of an alkyl-diol silica precolumn in a column-switching system for the determination of meloxicam in plasma.

The group of LiChrospher alkyl-diol silica (ADS) phases that make part of the unique family of restricted-access materials, have been developed as special packings used in the liquid chromatographic integrated sample processing of biofluids. The advantage of these phases lies in the possibility of direct injection of untreated plasma. An on-line elimination of the protein matrix is achieved with a quantitative recovery together with an on-column enrichment. The present method describes a hand-operated on-line switching high-performance liquid chromatographic system for the determination of meloxicam. Spiked plasma samples were introduced on the ADS precolumn using a 0.05 M phosphate buffer, pH 6.0. After washing with the buffer the ADS column was backflushed with the mobile phase 0.05 M phosphate buffer-30% (v/v) acetonitrile (ACN)-25 mM t-butylamine (TBA) at a pH of 7.0, thus transferring the analyte to the analytical column LiChrocart 125-4 LiChrospher RP-8. The eluent was monitored by a UV-detector set at 364 nm. The developed column-switching method is fully applicable to plasma injections.