A silica fiber coated with a ZnO-graphene oxide nanocomposite with high specific surface for use in solid phase microextraction of the antiepileptic drugs diazepam and oxazepam

A novel ZnO-graphene oxide nanocomposite was prepared and is shown to be a viable coating on fused silica fibers for use in solid phase microextraction (SPME) of diazepam and oxazepam from urine, this followed by thermal desorption and gas chromatographic quantitation using a flame ionization detector. A central composite design was used to optimize extraction time, salt percentage, sample pH and desorption time. Limits of detection are 0.5 μg·L⁻¹ for diazepam and 1.0 μg·L⁻¹ for oxazepam. Repeatability and reproducibility for one fiber (n = 4), expressed as the relative standard deviation at a concentration of 50 μg·L⁻¹, are 8.3 and 11.3% for diazepam, and 6.7 and 10.1% for oxazepam. The fiber-to-fiber reproducibility is <17.6%. The calibration plots are linear in the 5.0–1000 μg·L⁻¹ diazepam concentration range, and from 1.0–1000 μg·L⁻¹ in case of oxazepam. The fiber for SPME has high chemical and thermal stability (even at 280 °C) after 50 extractions, and does not suffer from a reduction in the sorption capacity. .