Determination of tramadol in human plasma and urine samples using liquid phase microextraction with back extraction combined with high performance liquid chromatography

Liquid phase microextraction by back extraction (LPME–BE) combined with high performance liquid chromatography (HPLC)-fluorescence detection was developed for the determination of tramadol in human plasma. Tramadol was extracted from 2 mL of basic sample solution (donor phase) with pH 11.5 through a micro liter-size organic solvent phase (100 μL n-octane) for 25 min and finally into a 3.5 μL acidic aqueous acceptor microdrop with pH 2.5 suspended in the organic phase from the tip of a HPLC microsyringe needle for 15 min with the stirring rate of 1250 rpm. After extraction for a period of time, the microdrop was taken back into the syringe and injected into HPLC. Effected the experimental parameters such as the nature of the extracting solvent and its volume, sample temperature, stirring rate, volume of the acceptor phase, pH and extraction time on LPME–BE efficiency was investigated. At the optimized condition, enrichment factor of 366 and detection limit (LOD) of 0.12 μg L−1 were obtained. The calibration curve was linear (r = 0.999) in the concentration range of 0.3–130 μg L−1. Within-day relative standard deviation RSD (S/N = 3) and between-day RSD were 3.16% and 6.29%, respectively. The method was successfully applied to determine the concentration of tramadol in the plasma and urine samples and satisfactory results were obtained.