Guanidinium ionic liquid-based surfactants as low cytotoxic extractants: Analytical performance in an in-situ dispersive liquid–liquid microextraction method for determining personal care products

Abstract

The IL-based surfactant octylguanidinium chloride (C8Gu-Cl) was designed and synthetized with the purpose of obtaining a less harmful surfactant: containing guanidinium as core cation and a relatively short alkyl chain. Its interfacial and aggregation behavior was evaluated through conductivity and fluorescence measurements, presenting a critical micelle concentration value of 42.5 and 44.6 mmol L−1, respectively. Cytotoxicity studies were carried out with C8Gu-Cl and other IL-based and conventional surfactants, specifically the analogue 1-octyl-3-methylimidazolium chloride (C8MIm-Cl), and other imidazolium- (C16MIm-Br) and pyridinium- (C16Py-Cl) based surfactants, together with the conventional cationic CTAB and the conventional anionic SDS. From these studies, C8Gu-Cl was the only one to achieve the classification of low cytotoxicity. An in situ dispersive liquid–liquid microextraction (DLLME) method based on transforming the water-soluble C8Gu-Cl IL-based surfactant into a water-insoluble IL microdroplet via a simple metathesis reaction was then selected as the extraction/preconcentration method for a group of 6 personal care products (PCPs) present in cosmetic samples. The method was carried out in combination with high-performance liquid chromatography (HPLC) and diode array detection (DAD). The method was properly optimized, requiring the use of only 30 μL of C8Gu-Cl for 10 mL of aqueous sample with a NaCl content of 8% (w/v) to adjust the ionic strength and pH value of 5. The metathesis reaction required the addition of the anion exchange reagent (bis[(trifluoromethyl)sulfonyl]imide − 1:1 molar ratio), followed by vortex and centrifugation, and dilution of the final microdroplet up to 60 μL with acetonitrile before the injection in the HPLC-DAD system. The optimum in situ DLLME-HPLC-DAD method takes ∼10 min for the extraction step and ∼22 min for the chromatographic separation, with analytical features of low detection limits: down to 0.4 μg L−1; high reproducibility: with RSD values lower than 10% (intra-day) and 16% (inter-day) for a spiked level of 15 μg L−1; and an average enrichment factor of 89. The requirement of low volumes (30 μL) of a low cytotoxic IL-based surfactant allows the method to be considered less harmful than other common analytical microextraction approaches.