Ionic liquid-based miniaturized aqueous biphasic system to develop an environmental-friendly analytical...

Two ILs containing guanidinium cations (butylguanidinium chloride -C₄Gu-Cl- and hexylguanidinium chloride -C₆Gu-Cl-) were synthesized and characterized. Their cytotoxicity was also assessed, obtaining adequate CC₅₀ values of 680 ± 99 mg·L^-1 for C₄Gu-Cl and 135 ± 8 mg·L^-1 for C₆Gu-Cl. Miniaturized aqueous biphasic systems (μ-ABSs) were developed using amounts lower than 1% (w/w) of these synthesized guanidinium-based ILs, K₃PO₄ as salting-out agent, and ultrapure water. The phases diagrams of both systems were determined, and the C₄Gu-Cl-based μ-ABS was selected for the development of a microextraction method in combination with high performance liquid chromatography (HPLC) with fluorescence detection (FD) for the determination of five polycyclic aromatic hydrocarbons (PAHs) as model analytes. A point of the biphasic region of the C₄Gu-Cl-based μ-ABS corresponding to a mixture of 0.75% (w/w) of the IL, 37.7% (w/w) of K₃PO₄ and 61.55% (w/w) of ultrapure water, and 30 min of equilibrium time, were selected as optimum conditions to obtain high enrichment factors and proper analytical microextraction performance. The C₄Gu-Cl-based μ-ABS-HPLC-FD method exhibited low limits of detection, between 0.010 ng·L^-1 and 2.0 ng·L^-1, average relative recoveries of 96.7%, high enrichment factors ranging from 44.1 to 60.4, average extraction efficiencies of 61.7%, and intermediate precision relative standard deviations lower than 17% for a concentration level of 12 ng·L^-1. The developed method was applied successfully in the analysis of different tap water samples.