An ionic liquid functionalized graphene adsorbent with multiple adsorption mechanisms for pipette-tip solid-phase extraction of auxins in soybean sprouts

A new ionic liquid functionalized graphene-pipette-tip solid-phase extraction method coupled with high-performance liquid chromatography was established for the simultaneous extraction and determination of three auxins in soybean sprouts. The graphene adsorbent, with multiple adsorption mechanisms, was first synthesized by functional modification of pentafluorobenzyl imidazolium bromide ionic liquid through thiol-ene click chemistry. The ionic liquid was applied to prevent the aggregation of graphene; it also imbued graphene with the ability for π-π interactions, ionic exchange, electrostatic interactions, as well as hydrogen bonding (which is stronger than the interaction between water and analytes), by augmenting the adsorption mechanisms between the adsorbent and analytes. Under optimized conditions, linearity was achieved in the ranges 0.03–5.00 µg/g for indole-3-acetic acid and 1-naphthaleneacetic acid and 0.09–5.00 µg/g for 2,4-dichlorophenoxyacetic acid, with a detection limit of 0.004–0.026 µg/g; this adsorbent has been successfully applied for the determination of auxins in soybean sprouts.