Use of switchable solvents in the microextraction context.

In this article, a new homogeneous liquid-liquid microextraction alternative, based on the use of switchable hydrophilicity solvents (SHS), is presented for the first time. The extraction technique makes use of a water-immiscible solvent (N,N-Dimethylcyclohexylamine) that can be solubilised in 1:1 ratio using CO2 as reagent. After the extraction, phases' separation is induced by the addition of sodium hydroxide, which produces a change on the ionisation state of the amine, centrifugation not being necessary. The extraction technique has been optimised and characterised using the determination of benz[a]anthracene by fluorimetric measurements in water samples as model analytical problem. Although the native fluorescence of the compound is quenched in the organic phase, this attenuation is reduced by diluting the extractant (1:1) in acetic acid. The fluorescence intensity is 35% higher in the SHS-acetic acid mixture than that obtained in pure methanol. The proposed method allows the determination of the target analyte with limit of detection of 0.08 μg/L and good precision (relative standard deviation of 6.7% at the limit of quantification level). The recoveries were in the range of 72-100% fulfilling the Environmental Protection Agency criterion. Finally, the potential use of this microextraction technique in combination with gas chromatography is shown for several polycyclic aromatic hydrocarbons.