Automated liquid chromatographic determination of atenolol in plasma usingdialysis and trace enrichment on a cation-exchange precolumn for sample handling

A fully automated method involving dialysis combined with trace enrichment was developed for the liquid chromatographic (LC) determination of atenolol , a hydrophilic P-blocking agent, in human plasma. The plasma samples were dialysed on a cellulose acetate membrane and the dialysate was reconcentrat ed on a short trace enrichment column (TEC) packed with a strong cation-exc hange material. All sample handling operations can be executed automaticall y by a sample processor (ASTED system). After TEC conditioning, the plasma sample, to which the internal standard (sotalol, another hydrophilic P-bloc ker) was automatically added, was introduced in the donor channel and dialy sed in the static/pulsed mode. The dialysis liquid consisted of 4.3 mM phos phoric acid. When the dialysis process was discontinued, the analytes were eluted from the TEC in the back-flush mode by the LC mobile phase and trans ferred to the analytical column, packed with octyl silica. The LC mobile ph ase consisted of phosphate buffer, pH 7.0-methanol (81:19; v/v) with 1-octa nesulfonate. Atenolol and the internal standard were monitored photometrica lly at 225 nm. The different parameters influencing the dialysis and trace enrichment processes were optimised with respect to analyte recovery. The i nfluence of two different kinds of cation-exchange material on analyte reco very and peak efficiency was also studied. The method was then validated in the concentration range 25-1000 ng/ml. The mean recovery for atenolol was 65% and the limit of quantitation was 25 ng/ml. (C) 2000 Elsevier Science B .V. All rights reserved.