Effective extraction of the metabolites of toluene and xylene based on a postsynthetic-modified magnetic covalent organic polymer

Toluene and xylene are volatile organic compounds, and long-term exposure to toluene and xylene may cause brain structure and nervous system damage. To evaluate exposure to toluene and xylene in the environment, it is usually possible to monitor their metabolites in organisms, hippuric acid (HA) and methylhippuric acid (MHA). In this work, we designed a new magnetic solid phase extraction (MSPE) sorbent, zirconium postsynthetic-modified magnetic covalent organic polymer (Fe3O4@COP-COOZr), for purifying and enriching HA and 4-MHA. Zirconium ions were immobilized on the magnetic COP surface by postsynthetic modification without the use of additional coating layers or chelating ligands. The developed Fe3O4@COP-COOZr interacted with HA and 4-MHA through the π-π stacking effect and electrostatic interactions, as well as strong chelation with coordinatively unsaturated zirconium sites. The promising affinity material of Fe3O4@COP-COOZr in MSPE had high stability and recyclability. The established MSPE-HPLC-UV method showed low sorbent consumption (10 mg) and high sensitivity (LODs less than 0.1 μg L−1), and can be used for the analysis of HA and 4-MHA in real samples. The recoveries of the proposed method in real urine samples for the simultaneous determination of HA and 4-MHA were in the range of 83.5–103.2 %, and the RSDs were 0.9–7.1 %.