Solid‐phase microextraction of ultra‐trace amounts of tramadol from human urine by using a carbon nanotube/flower‐shaped zinc oxide hollow fiber

A new method is successfully developed for the separation and determination of a very low amount of tramadol in urine using functionalized multiwalled carbon nanotubes/flower-shaped zinc oxide before solid-phase microextraction combined with gas chromatography. Under ultrasonic agitation, a sol of multiwalled carbon nanotubes and flower-shaped zinc oxide were forced into and trapped within the pore structure of the polypropylene and the sol solution immobilized into the hollow fiber. Flower-shaped zinc oxide was synthesized and characterized by Fourier transform infrared spectroscopy. The morphology of the fabricated solid-phase microextraction surface was investigated by scanning electron microscopy and X-ray diffraction. The parameters affecting the extraction efficiencies were investigated and optimized. Under the optimized conditions, the method shows linearity in a wide range of 0.12-7680 ng/mL, and a low detection limit (S/N = 3) of 0.03 ng/mL. The precision of the method was determined and a relative standard deviation of 3.87% was obtained. This method was successfully applied for the separation and determination of tramadol in urine samples. The relative recovery percentage obtained for the spiked urine sample at 1000 ng/mL was 94.2%.