Combined extraction and microextraction techniques: Recent trends and future perspectives

In situ formation of hydrophobic magnetic ionic liquids for dispersive liquid-liquid microextraction

A new class of magnetic ionic liquid (MIL) containing paramagnetic cations has been applied for in situ dispersive liquid-liquid microextraction in the determination of both polar and non-polar pollutants, including ultraviolet filters, polycyclic aromatic hydrocarbons, alkylphenols, a plasticizer and a preservative in aqueous samples. The MILs were based on cations containing Ni(II) metal centers coordinated with four N-alkylimidazole ligands and chloride anions. The MILs were capable of undergoing in situ metathesis reaction with the bis[(trifluoromethyl)sulfonyl]imide ([NTf₂^-]) anion during the microextraction procedure, generating a water-immiscible extraction solvent containing the preconcentrated analytes. The MIL was then isolated by magnetic separation, followed by direct analysis using reversed-phase high performance liquid chromatography with diode array detection. Among all of the studied MILs, those containing the N-butylimidazole and N-benzylimidazole ligands ([Ni(C₄IM)₄²⁺]2[Cl^-] and [Ni(BeIM)₄²⁺]2[Cl^-], respectively) exhibited the best extraction performance. The method under optimum conditions required 5 mL of sample at pH 3, 20 mg of [Ni(C₄IM)₄²⁺]2[Cl^-] or 30 mg of [Ni(BeIM)₄²⁺]2[Cl^-], 300 μL of acetone or acetonitrile as dispersive solvent (depending on the MIL), a 1:2 M ratio of MIL to [NTf₂^-], and 3 min of vortex. The developed method achieved higher extraction efficiency compared to the conventional MIL-dispersive liquid-liquid microextraction mode, with extraction efficiencies of 46.8-88.6% and 65.4-97.0% for the [Ni(C₄IM)₄²⁺]2[Cl^-] and the [Ni(BeIM)₄²⁺]2[Cl^-] MILs (at a spiked level of 81 μg L^-1), respectively, limits of detection down to 5.2 μg L^-1, and inter-day relative standard deviation lower than 16%.

Current status and future trends on automated multidimensional separation techniques employing sorbent-based extraction columns

Determination of target analytes present in complex matrices requires a suitable sample preparation approach to efficiently remove the analytes of interest from a medium containing several interferers while at the same time preconcentrating them aiming to improve the output signal detection. Online multidimensional solid-phase separation techniques have been widely used for the analysis of different contaminants in complex matrices such as food, environmental, and biological samples, among others. These online techniques usually consist of two steps performed in two different columns (extraction and analytical column), the first being employed to extract the analytes of interest from the original medium and the latter to separate them from the interferers. The extraction column in multidimensional techniques presents a relevant role since their variations as building material (usually a tube), sorbent material, modes of application, and so on can significantly influence the extraction success. The main features of such columns are subject of constant research aiming improvements directly related to the performance of the separation techniques that utilize multidimensional analysis. The present review highlights the main features of extraction columns online coupled to chromatographic techniques, inclusive for in-tube solid-phase microextraction, online solid phase and turbulent flow, aiming the determination of analytes present at very low concentrations in complex matrices. It will critically describe and discuss some of the most common instrumental set up as well as comments on recent applications of these multidimensional techniques. Besides that, the authors have described some properties and enhancements of the extraction columns that are used as first dimension on these systems, such as type of column material (poly (ether ether ketone), fused silica, stainless steel, and other materials) and the way that the extractive phase is accommodated inside the tubing (filled and open tubular). Practical applications of this approach in fields such as environment, food, and bioanalysis are also presented and discussed.

Combination of dispersive solid phase extraction and deep eutectic solvent-based air-assisted liquid-liquid microextraction followed by gas chromatography-mass spectrometry as an efficient analytical method for the quantification of some tricyclic antidepressant drugs in biological fluids

A dispersive solid phase extraction coupled with deep eutectic solvent-based air-assisted liquid-liquid microextraction has been developed and applied to the extraction and preconcentration of some tricyclic antidepressant drugs in the human urine and plasma samples prior to their determination by gas chromatography-mass spectrometry. In this method, a sorbent (C₁₈) is first added into an alkaline aqueous sample and dispersed by vortexing. By this action, the analytes are adsorbed onto the sorbent. Then, the sorbent particles are isolated from the aqueous solution by centrifugation. Afterward, a deep eutectic solvent, prepared from choline chloride and 4-chlorophenol is used to desorb the analytes from the sorbent. Subsequently, the supernatant solution is removed and added into an alkaline deionized water placed into a test tube with a conical bottom. The resulting mixture is rapidly sucked into a glass syringe and then injected into the tube. This procedure is repeated for several times and a cloudy solution consisting of fine droplets of deep eutectic solvent dispersed into the aqueous phase is formed. After centrifuging the obtained cloudy solution, the tiny droplets of the extractant, containing the extracted analytes, settle at the bottom of the tube. Finally, an aliquot of the extractant is taken and injected into the separation system for quantitative analysis. Several significant factors affecting the performance of the proposed method are evaluated and optimized. Under optimum extraction conditions, the method shows low limits of detection in the ranges of 5-10, 8-15 and 32-60 ng L^-1 in deionized water, urine, and plasma, respectively. Enrichment factors are observed to be between 325 to 385 in deionized water, 155 to 185 in urine, and 64 to 72 in plasma. Extraction recoveries are in the range of 65-77 (in deionized water), 62-74 (in urine), and 64-72% (in plasma). The relative standard deviations of the proposed method are ≤ 6% for intra- (n = 6) and inter-day (n = 4) precisions at a concentration of 200 ng L^-1 of each analyte. Finally, the applicability of the introduced method is investigated by analyzing the selected drugs in different biological fluids. In the proposed method, for the first time, a deep eutectic solvent composed of safe, cheap, and biodegradable compounds was synthesized and used (at μL-level) as an elution and extraction solvent, simultaneously which led to omit the consumption of toxic organic solvents. This represents a significant advantage in the era of green chemistry. In addition, the introduced method is sensitive, simple in operation, rapid, and efficient.