Determination of phosphonoformate (foscarnet) in calf and human serum by automated solid-phase extraction and high-performance liquid chromatography with amperometric detection

An isocratic high-performance liquid chromatographic method with automated solid-phase extraction has been developed to determine foscarnet in calf an d human serums. Extraction was performed with an anion exchanger, SAX, from which the analyte was eluted with a 50 mM potassium pyrophosphate buffer, pH 8.4. The mobile phase consisted of methanol-40 mM disodium hydrogenphosp hate, pH 7.6 containing 0.25 mM tetrahexylammonium hydrogensulphate (25:75, v/v). The analyte was separated on a polyether ether ketone (PEEK) column 150x4.6 mm I.D. packed with Kromasil 100 C-18, 5 mu m. Amperometric detecti on allowed a quantification limit of 15 mu M. The assay was linear from 15 to 240 mu M. The recovery of foscarnet from calf serum ranged from 60.65 +/ - 1.89% for 15 mu M to 67.45 +/- 1.24% for 200 mu M. The coefficient of var iation was less than or equal to 3.73% for intra-assay precision and less t han or equal to 7.24% for inter-assay precision for calf serum concentratio ns ranged from 15 to 800 mu M. For the same samples, the deviation from the nominal value ranged from -8.97% to +5.40% for same day accuracy and from -4.50% to +2.77% for day-to-day accuracy. Selectivity was satisfactory towa rds potential co-medications. Replacement of human serum by calf serum for calibration standards and quality control samples was validated. Automation brought more protection against biohazards and increase in productivity fo r routine monitoring and pharmacokinetic studies. (C) 1999 Elsevier Science B.V. All rights reserved.