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The accuracy of free drug measurement by CF-UF was albumin concentration dependent. However, such an effect was not observed when samples were prepared by HFCF-UF, which was more suitable for TDM of plasma samples from different patients. Therefore, this method could be readily applied to the measurement of free valproic acid plasma concentrations for TDM in patients.

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A sensitive and reliable method using a two-phase hollow fiber liquid-phase microextraction (HF-LPME) pretreatment technique was developed for simultaneously screening multiple b-blockers in environmental samples. In this study, heptanol was chosen as the optimal extraction solvent, and six bblockers with a wide range of polarities were extracted across the porous walls of hollow fibers and into the acceptor phase (AP). The fundamental parameters affecting the extraction efficiency (EE) of analytes including extraction time, temperature, pH of the donor phase (DP) and AP, stirring speed, volume of the sample solution, ionic strength and the type of hollow fiber membrane were studied and optimized.Under optimal conditions, extracts were analyzed by HPLC with ultraviolet detection (UV). Finally, satisfactory results were obtained, good linearity was observed for all b-blockers in the range of 0.16-200 ng mL À1 , limits of detection (LODs) were between 0.08 and 0.5 ng mL À1 , the intra-and inter-day precision values of the six b-blockers were 1.0-2.2% and 1.4-2.7%, respectively. The recovery with RSDs was less than 2.2% for the pretreatment method. The proposed technique was successfully applied for screening multiple b-blockers in complex aqueous samples with the best specificity and provided a simple and reliable new means for the self-checking of laboratories at the basic level.

The selectivity of a suitable organic solvent is key for extraction in liquid-phase microextraction experiments. Nevertheless, the screening process remains a daunting task. Our research aimed to study the relationship between extraction efficiency and extraction solvents, analytes, and finally select the appropriate extraction solvent. In the present article, β-blockers and six extraction solvents were chosen as the models and hollow-fiber liquid-phase microextraction was conducted. The relationship was built by statistical analysis on the data. Factors affecting extraction efficiency including the logarithms of the octanol/water partition coefficient (logPo/w ) of analytes, acid dissociation constants, the logarithms of the octanol/water partition coefficient of solvents and pH of the sample solution were investigated. The results showed that a low water solubility of extraction solvent is the foundation to ensure higher extraction efficiency. Moreover, when ΔlogPo/w > 0, a higher extraction efficiency is observed at lower ΔlogPo/w , on the contrary, when ΔlogPo/w < 0, extraction efficiency is higher as the absolute value of ΔlogPo/w becomes greater. Finally, the relationship between enrichment factor and extraction solvents, analytes was established and a helpful guidance was provided for the selection of an optimal solvent to obtain the best extraction efficiency by liquid-phase microextraction.