Effective tuning guanidinium ionic liquid as greener solvent for fast and sensitive determination of auxin herbicides

Auxin herbicides have attracted continuously increasing attention because of their frequently application worldwide, slow degradation rates and potential toxicity to human beings. It is urgent to develop a fast and practical method to monitor them in environmental samples. Ionic liquids (ILs) are not intrinsically "green" and most of them are as toxic as other solvents. Therefore, tuning for maximizing advantageous properties of ILs and minimizing side effects are crucial steps. In this work, guanidinium IL was applied to preconcentrate and clean up ultra-trace auxin herbicides via designable binding sites. The structurally optimized IL had improved pretreatment performance and was significantly less cytotoxic than imidazolium IL toward human keratinocytes. For further improving the sensitivity of detection, we quantified the concentration of herbicides by a fast and mild fluorescence derivatization. Under optimized pretreatment conditions, high recoveries in real water samples (above 80%), short pretreatment time (< 3 min for microextraction; 8 min for derivatization) and extremely low limit of detection values (3.90-12.40 ng L-1) were achieved. The proposed method was successfully applied to the analysis of real water samples.