Development of a hollow fiber–liquid phase microextraction method using tissue culture oil for the extraction of free metoprolol from plasma samples

•A hollow fiber–liquid phase microextraction method was developed for extraction of free metoprolol from plasma samples.•Tissue culture oil was used as the extraction solvent for the first time.•HPLC-DAD was used as the determination instrument for monitoring of the analyte.•Easiness, good extraction performance and reliable analysis are the advantages of the method. In this research, a method known as a hollow fiber-liquid-phase microextraction was employed to extract and concentrate free metoprolol from plasma samples. The extracted analyte was subsequently determined using high-performance liquid chromatography coupled with a diode-array detector. Several parameters, including hollow fiber length, sonication time, extraction temperature, and salt addition, were investigated and optimized to enhance extraction efficiency. After extracting the analyte under optimum conditions from plasma samples, the enrichment factor and extraction recovery were 50 and 86 %, respectively. Moreover, the method exhibited detection and quantification limits of 0.41 and 1.30 ng mL−1, respectively. The analysis of real samples demonstrated satisfactory relative recoveries in the range of 91–99 %.