Zeolite imidazolate framework-67 reinforced hollow-fiber liquid-phase microextraction of typical flavor enhancers in dairy products followed by electrophoretic analysis

In this work, the porous nanomaterial zeolite imidazolate framework-67 (ZIF-67) and tributyl phosphate (TBP) were introduced to co-modify the hollow-fiber liquid-phase microextraction (HF-LPME) for the first time. The extract of five typical flavor enhancers (vanillin, o-vanillin, ethyl vanillin, vanillinol and vanilla acetone) could be directly injected for electrophoretic separation and amperometric detection. The obtained optimum extraction conditions were as followed: supported liquid membrane, tributyl phosphate containing 0.050   mg   mL -1 of ZIF-67; donor phase, 10   mL (pH 4.00 adjusted by HCl); acceptor phase, 10   μL (0.20   M NaOH); stirring rate, 500   rpm; extraction temperature, 25 °C; and extraction time, 45   min. Based on the synergistic enrichment effect of ZIF-67 and TBP, this HF-LPME could provide the enrichment factors of 207(V-OH)-890 times (EVA) for the flavor enhancers. This method has been successfully used for the analyses of milk, milk powder and milk tea samples. The limits of detection were 0.15-3.0   μg   L -1 (S/N=3), and the recovery data were in the range of 80.1-115.5%. This developed method is easy to operate and has low consumption of solvents and samples, providing a green alternative method for the detection of typical flavor enhancers in dairy products. Besides, the greenness and eco-friendliness of the proposed method was assessed using the green analytical procedure index and analytical eco-scale tools.