A covalently cross-linked microporous polymer based micro-solid phase extraction for online analysis of trace pesticide residues in citrus fruits.

Covalently cross-linked microporous polymers are a new class of highly cross-linked porous network materials with large surface area and potential superiority in sample pretreatment. In this work, a covalently cross-linked microporous polymer was well designed and synthesized by condensation of acylhydrazines in terephthalic dihydrazide with aldehyde groups in 1,3,5-benzenetricarboxaldehyde. The adsorption mechanism was explored and discussed based on π-π stacking interaction and steric effect. Then, a covalently cross-linked microporous polymer was employed as the adsorbent of online micro-solid-phase extraction coupled with high-performance liquid chromatography for the enrichment and analysis of trace pesticide residues in citrus fruits. The method was successfully applied to the online analysis of sugar orange and Huangdigan samples with the detection limits of 0.10-0.30 µg/kg. It was satisfactory that chlorpifos and triazophos in real sugar orange and Huangdigan samples could be actually found and quantified at concentrations of 0.20 and 0.51 mg/kg, respectively. The recoveries of sugar orange and Huangdigan samples were in the range of 70.0-103 and 74.0-119% with relative standard deviations of 0.4-9.7 and 0.5-9.2% (n = 3), respectively. The proposed method was accurate, reliable, and convenient for the online simultaneous analysis of trace pesticide residues in citrus fruits.