A hollow fiber solid phase microextraction method for preconcentration of venlafaxine and o-desmethylvenlafaxinein biological matrices is described for the first time. The functionalized MWCNTs with an amino acid,glycine, were synthesized and held in the pore of a hollow fiber by sol-gel technique. In order to extractvenlafaxine and o-desmethylvenlafaxinefromreal samples, the hollow fiber wasimmersed into the sample solutionunder a magnetic stirring for 20 min.Theextractedvenlafaxine and o-desmethylvenlafaxinefrom the fibers were then desorbed with methanol by sonication and analyzed using high performance liquid chromatography. Important microextraction parameters including pH of donor phase, donor phase volume, stirring rate, extraction time, and desorption conditions such as the type and volume of solvents and desorption time were thoroughly investigated and optimized.The optimized technique provides good repeatability (RSD of the intraday precision 3.7 and 3.4, interday precision of 5.8 and 5.4%), linearity of (0.1- 300 and 0.2- 360ng mL-1), low LODs of (0.03 ng mL-1 and 0.07 ng mL-1) and high enrichment factor of (164 and 176) for venlafaxine and o-desmethylvenlafaxine, respectively.The analytical performance of Gly-MWCNTs as a new SPME sorbent was compared with MWCNTs andcarboxylic MWCNTs. The results indicate that Gly-MWCNTs are quite effective for extraction of venlafaxine and o-desmethylvenlafaxine. Feasibility of the method was evaluated by analyzing human urine and real water samples. The results obtained in this work show a promising, simple, selective and sensitivesample preparation and determination method for biological and water samples.

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