Determination of mefenamic acid in urine and pharmaceutical samples by HPLC after pipette-tip solid phase microextraction using zinc sulfide modified carbon nanotubes

In this work, a novel pipette-tip solid phase microextraction based on a carbon nanotube-zinc sulfide (CNTs-ZnS) nano-composite, as a selective sorbent, was developed and applied for the extraction and HPLC determination of trace amounts of mefenamic acid in urine samples. The CNT-ZnS nanocomposite was synthesized by electrophoretic deposition on aluminum sheets. Parameters affecting the extraction efficiency were investigated and optimized. The method was found to be linear in the range of 0.7-100 mg L-1 with good linearity (r(2) > 0.989). The limit of detection was calculated to be 0.075 mu g L-1 and the relative standard deviation for 50 mg L-1 of the analyte in aqueous solution (n = 5) was 4.2%. Moreover, a short analysis time of 9 min was achieved. Finally, the method was successfully applied to the extraction and preconcentration of mefenamic acid in pharmaceutical and urine samples.