A simple and sensitive liquid phase microextraction procedure based on solidification of a floated organic drop microextraction (SFDME) has been developed for the determination of thiamine and cobalamine in serum and urine samples. The extracts were analyzed by isocratic reverse phase high performance liquid chromatography (RP-HPLC) and UV detection. The procedure has been optimized with respect to type and volume of extraction solvent, salting out, pH, stirring rate, and time of extraction. The calibration graphs were linear for the both analytes over the concentration range of 5-400 μg/L, and coefficients of determination ranged from 0.994 to 0.998. The limits of detection were in the ranges of 3.1-9.2 μg/L. Intra-day and inter-day precisions for peak areas were in the range of 2.2-4.1% and 1.7-4.3%, respectively. The proposed procedure was successfully applied to the determination of analytes in spiked urine and serum samples with satisfactory results. The relative recoveries of spiked urine and serum samples ranged from 90.5 to 106.8%, with relative standard deviations varying from 2.5 to 4.3%. This method is simple, fast, precise, reproducible, linear over a wide range, sensitive, and especially suitable for the determination of trace amount of thiamine and cobalamine in biological samples.
