Corncob biochar as a coating for trace analysis of polycyclic aromatic hydrocarbons in water samples by online in-tube solid-phase microextraction coupled to high performance liquid chromatography

Abstract

Biochar materials have been focused on enormous attention in the fields of capacitance, catalysis, adsorption due to its renewability, abundant in content and widespread distribution. In this work, corncob biochar materials were prepared under different carbonized temperature and characterized by scanning electron microscopy and Raman spectroscopy for surface morphology and graphitization degree. Then the materials were separately attached onto stainless steel wires as the coatings for solid-phase microextraction (SPME). Four wires with the same coating were placed into a polyetheretherketone tube to develop several extraction tubes. Coupled to high performance liquid chromatography (HPLC) with diode array detector (DAD), the tubes were evaluated using several polycyclic aromatic hydrocarbons (PAHs) as model analytes. According to the comparison of extraction efficiency, the best tube was selected. To achieve high sensitivity, both main extraction and desorption processes were optimized. Under the optimum conditions, an in-tube SPME-HPLC-DAD method for PAHs was established with low limits of detection (0.003–0.030 ng mL−1), wide linear ranges (0.010–15 ng mL−1, 0.017–15 ng mL−1, 0.033–15 ng mL−1 and 0.099–15 ng mL−1), high enrichment factors (1864–2615) and acceptable repeatability (relative standard deviations (RSDs, n = 3) less than 2.9% and 6.7% for intra-day and inter-day tests). Furthermore, the accuracy of the method was investigated via analyzing trace PAHs in real water samples and good recoveries (81.7%-116.8%) were obtained. In addition, the extraction tube exhibited satisfactory durability and chemical stability (RSDs ≤ 8.0%, n = 3) and acceptable reproducibility (RSD ≤ 7.8%, n = 3).