Semicarbazide, a toxic food contaminant, widely exists in food products and it originates from the thermal degradation of a food additive of azodicarbonamide or a metabolite of nitrofurazone abused in meat specimens. Many previous methods for semicarbazide determination usually required expensive instruments, difficult-to-prepare monoclonal antibodies, and a long operation time. In this study, a high-performance liquid chromatography method was developed for the rapid determination of trace semicarbazide coupling with a nucleophilic substitution reaction firstly using 4-nitrobenzoyl chloride as derivatization reagent. The derivatization reaction was mild at room temperature for 1 min in neutral solution. Then, semicarbazide derivative was separated and quantified by high-performance liquid chromatography with ultraviolet detection under optimal separation conditions at λ = 261 nm. The proposed method offered the detection limit of 1.8 μg/L and was successfully applied for the rapid determination of trace semicarbazide in flour products. Semicarbazide in positive real samples could be actually found and quantified in the range of 0.47-7.53 mg/kg. The recoveries were 76.6-119% with relative standard deviations of 0.5-9.1% (n = 3). This developed method was rapid, reliable, and convenient for the determination of trace semicarbazide in food.
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.
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