Determination of human plasma protein binding of baicalin by ultrafiltration and high‐performance liquid chromatography

A simple and selective HPLC assay was developed and utilized for determination of human plasma protein binding of baicalin. The method involved solid‐phase extraction and reversed‐phase chromatographic separation with a mobile phase of acetonitrile−0.02 mol/L phosphate buffer (pH 2.5; 25:75, v/v) and UV detection at 276 nm. The standard curve for baicalin was linear over the concentration range 0.1–20 µg/mL and the limit of detection was 0.02 µg/mL. The absolute recovery was greater than 76%. The intra‐day and inter‐day variations were less than 10%. Ultrafiltration technique was applied to determining the plasma protein binding of baicalin in human plasma. Results show the plasma protein binding of baicalin was in the range 86–92% over all the concentrations studied and the protein binding association constant was determined to be 1.21 × 10 5 L/mol at 4°C. Copyright © 2006 John Wiley & Sons, Ltd.