Preconcentration/extraction of trace bisphenols in milks using a novel effervescent reaction-assisted dispersive solid-phase extraction based on magnetic nickel-based N-doped graphene tubes

Abstract

The drawbacks of conventional carbon-based nanotubes lie in no magnetism, less structural defects and reactive sites, thereby leading to a poor adsorption/extraction performance. Herein, we synthesized Ni-based N-doped graphene tubes (Ni@N-GrTs), which were used for effervescent reaction-assisted dispersive solid-phase extraction (mETDSE/Ni@N-GrTs) of trace bisphenols (BPs) in milks. This Ni@N-GrTs material not only had magnetism, but also increased the number of structural defects and reactive sites, thereby improving extraction efficiency and yielding convenient and rapid separation and collection. By Raman and XPS spectrum analysis, the N-doping atoms were proved to be existed as pyridine-like groups on the structure of Ni@N-GrTs, and the enhanced adsorption on BPs was attributed to increased number of defects, π-π interaction and hydrogen-bonding effect. With the aid of vigorous CO2 dispersion from effervescent reaction, the mETDSE/Ni@N-GrTs method realized highly efficient adsorption/extraction, rapid dispersion and magnetic separation and collection synchronously. The main variables were firstly screened on the basis of Plackett-Burman design, and the significant ones were then optimized using Box-Behnken design. Under optimized conditions, the newly developed method gave limits of detection of 0.1–0.2 μg/ L, and the intra- and inter-day precisions of 1.9–4.9% and 2.5–6.8%, respectively. The average extraction recoveries for BPA, BPB, BPAF and BPAP were in the range of 83.6–105.1% with relative standard deviations of 0.9–4.7% in whole-fat, low-fat and fat-skimmed milks as well as milky tea and infant milk powder. In general, the mETDSE/Ni@N-GrTs-HPLC-FLD method is simple, rapid, inexpensive, highly efficient and environmentally friendly, and thus it has great prospects in conventional monitoring of BPs in complex milk matrices.