Analysis of warfarin in plasma by high-pressure liquid chromatography

An improved high-pressure liquid chromatography method for the estimation of warfarin in plasma was developed. Plasma was acidified and extracted with ethylene dichloride spiked with methylated warfarin [3-(alpha-acetonylbenzyl)-4-methoxy-coumarin] as internal standard. The residue, redissolved in dioxane, was chromatographed on a reversed-phase column using a mobile phase of 40% dioxane in water (pH 4.2) on a high-pressure liquid chromatograph fitted with an UV absorbance detector. Recoveries from extraction, quantitated using tracer amounts of [14C]warfarin and methylated [14C]warfarin were 92.2 +/- 3.16% and 82.33 +/- 1.03%, respectively. The standard curve was linear between o.625 and 5.0 microng/ml. Detection was sensitive to approximately 0.5 microng/ml and specific without the inter ference of normal plasma constituents and warfarin metabolites.