Improved RPLC determination of acyclovir using hexylamine as silanol masking agent

The aim of the present work is to improve the sensitivity in the RPLC deter mination of acyclovir [9-(2-hydroxy ethoxymethyl) guanine] (ACV) and guanin e, the major impurity Of the drug synthesis and one of the compounds found in the chemical degradation process of ACV. The method was applied to the q uantification of drug in liposomal formulations. The most important problem for RPLC analysis of both compounds are their high pK(a) values, mainly gu anine, and the interaction with reactive silanol groups in the stationary p hase. In order to avoid these problems there are four basic strategies: (i) ionic pair reagents, (ii) deactivated silica columns, (iii) polymeric base d columns and (iv) silanol masking agents. A validation protocol was follow ed to develop the analytical method, using a Spherisorb ODS (250 x 4.6 mm i .d.) analytical column, with a mobile phase of 95% aqueous phosphate buffer (pH 3.0) and 5% HPLC methanol pumped isocratically at 1.3 mi min(-1), with ultraviolet: detection at 254 nm. The results showed a high reproducibilit y in retention time value, with R.S.D. of 2.37% for ACV and 0.32% for guani ne. The lowest concentration levels assayed, 0.15 mu g ml(-1) for guanine a nd 1 mu g ml(-1) for ACV, showed good R.S.D, in the quantification paramete r (peak area) 11.0% (guanine) and 9.64% (ACV) (C) 1999 Elsevier Science B.V . All rights reserved.