Determination of warfarin-human serum albumin protein binding parameters by an improved Hummel-Dreyer...

The Hummel-Dreyer size-exclusion high-performance liquid chromatographic method for the determination of protein binding parameters has been improved and automated by use of an internal surface reversed-phase (ISRP) column (5 cm X 4.6 mm) and a computer-controlled mobile-phase delivery system with low volume syringe mixing. The high-efficiency ISRP columns, which are nonadsorptive and exclusionary to serum proteins but allow partitioning of small molecules with an internal peptide bonded phase, maintain high performance after many injections of human serum albumin (HSA), enable the use of short columns, and provide for the resolution of primary ligand from protein binding displacers. The modified Hummel-Dreyer high-performance liquid chromatographic method was demonstrated by the determination of binding parameters for warfarin-HSA in phosphate buffer, which were found to be n1 = 1.0, n2 = 2.1, K1 = 3.30 X 10(5) M-1, and K2 = 2.03 X 10(4) M-1. The necessary sequence of chromatographic experiments was repeated 4 times at 18 separate warfarin mobile phase concentrations. Each automated sequence required 8 h to complete. The parameters were measured with a precision of less than 10% relative standard deviation.