Synthesis of spindle-like amino-modified Zn/Fe bimetallic metal-organic frameworks as sorbents for dispersive solid-phase extraction and preconcentration of phytohormoes in vegetable samples

Amino-modified Zn/Fe bimetallic metal–organic frameworks (NH 2 -Zn/Fe-MIL-88) were synthesized using a one-step solvothermal method with FeCl 3 ·6H 2 O and Zn(NO 3 ) 2 ·6H 2 O as metal salts and 2-aminoterephthalic acid as organic ligand. The morphology of NH 2 -Zn/Fe-MIL-88 can be regulated from octahedral-like to spindle-like with changing molar ratios of metal salts. Using NH 2 -Zn/Fe-MIL-88 as sorbent, a dispersive solid-phase extraction with putting sorbents into sample solution to extract targets was developed to preconcentrate phytohormones in vegetables. To study the extraction efficiency, a series of NH 2 -Zn/Fe-MIL-88s with varying molar ratios of metal salts were prepared. The results indicated that NH 2 -Zn/Fe-MIL-88(1) presented the highest extraction efficiency (82.6 %–98.1 %) to phytohormones among all prepared NH 2 -Zn/Fe-MIL-88(x). The limits of detection were calculated at 0.07–0.15 ng/mL. The adsorption isotherms and kinetic parameters of NH 2 -Zn/Fe-MIL-88 for phytohormones were conformed to Langmuir and pseudo-second-order models. The NH 2 -Zn/Fe-MIL-88 as sorbent combined with HPLC was applied to detect phytohormones in cucumber and tomato samples.