A method was established using hollow fiber-liquid phase microextraction（HF-LPME） followed by high performance liquid chromatography（HPLC） to determine the concentration of the free（unbound） drug in the solution of the drug and protein. Measurements of drug-protein binding ratios and free drug concentrations were then analyzed with the Klotz equation to determine the equilibrium binding constant and number of binding sites for drug-protein interaction. The optimized method allows one to perform the efficient extraction and separation of free drug from protein-bound drug, protein, and other interfering substances. This approach was used to characterize the binding of the anticholinergic drugs atropine sulfate and scopolamine hydrobromide to proteins in human plasma and bovine serum albumin（BSA）. The results demonstrate the utility of HF-LPME method for measuring free drug concentrations in protein-drug mixtures and determining the protein binding parameters of a pharmacologically important class of drugs.
Liquid-phase microextraction with back extraction （LPME-BE） combined with high performance liquid chromatography （HPLC） was investigated for the extraction and determination of magnolol and honokiol in Magnolia officinalis, a traditional Chinese medicine （TCM）, and its pharmaceutical preparations, Huo Xiang Zheng Qi peroral liquid and Xiang Sha Yang Wei pellet. Organic solvent, donor and acceptor phases, stirring rate and extraction limes were all factors which can influence the efficiency of extraction and were all optimized during the course of this work. Linear calibration curves were obtained in concentration ranges of 1,56-156 μg/mL for magnolol and 1.10-110 μg/mL for honokiol. Detection limits （S/N = 3） were 0.10 and 0.07 μg/mL, respectively. The relative recoveries were both in the range of 98.3% - 105.1% and RSD was lower than 2.5% .
