Nitrogen, Oxygen-Codoped Hierarchically Porous Biochar for Simultaneous Enrichment and Ultrasensitive Determination of O-Xylene and Its Hydroxyl Metabolites in Human Urine by Solid Phase Microextraction-Gas Chromatography-Mass Spectrometry

o-Xylene is carcinogenic to human and animals, and the exposure of it could cause serious health problems. The analysis of o-xylene and its hydroxyl metabolites is of great significance for monitoring human exposure and health care. Herein, low-cost waste biomass, bovine bone, has been carbonized to obtain nitrogen and oxygen codoped hierarchically porous biochar (NHPBC) with outstanding advantages, including high specific surface area and sufficient heteroatoms. After systematically investigating enrichment performance of NHPBC towards various organic pollutants, it has been proved that the prepared NHPBC is suitable for high-efficient enrichment of o-xylene and its hydroxyl metabolites. The enrichment factors of NHPBC-coated fiber are from 2384 to 6949, which are 11.1-92.5 times higher than those of commercial solid phase microextraction (SPME) fibers. Under the optimum condition (extraction for 50 min at 50 degrees C, and desorption at 330 degrees C for 5 min), an ultrasensitive method with low limits of detection (0.091-1.65 ng L-1), wide linear ranges (5-5000 ng L-1), and good reproducibility (2.19-7.28% for single fiber, n = 5, and 2.64-9.98% for fiber-to-fiber, n = 3) has been developed for simultaneous determination of o-xylene and its hydroxyl metabolites, by coupling NHPBC-coated fiber with gas chromatography-mass spectrometry. This study is expected to benefit for the applications of porous carbon in adsorption, and provide more approaches for the control and precise quantifications of volatile organic compounds (VOCs).