Microextraction Techniques Using Deep Eutectic Solvents

Microextraction techniques employing deep eutectic solvents (DESs) have emerged as a versatile and environmentally benign approach to trace-level separation and preconcentration of analytes from complex matrices. By combining a hydrogen bond acceptor and a hydrogen bond donor in precise ratios, DESs form eutectic mixtures that exhibit low volatility, adjustable polarity and strong solvating power for a wide range of organic and inorganic species. In microextraction, DESs may be deployed in liquid-phase modes—such as dispersive liquid-liquid microextraction or ultrasound-assisted microextraction—or in solid-phase formats after in situ solidification. These methods typically consume microlitre to millilitre volumes of solvent, achieving high enrichment factors, rapid kinetics and minimal waste generation. Applications have spanned environmental water analysis, food and beverage testing, biological fluid cleanup and the preconcentration of pesticides, dyes, phenolic compounds and metal ions. Key advantages include straightforward preparation of the solvent system, compatibility with chromatographic or spectroscopic detection and the capacity to tailor extraction selectivity by modifying DES composition and experimental parameters such as pH, temperature and extraction time. Collectively, DES-based microextraction offers an adaptable platform for green and cost-effective sample preparation, enhancing sensitivity and selectivity in analytical workflows.

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Recent advances have demonstrated the utility of natural deep eutectic solvents in ultrasound-assisted liquid-liquid microextraction for the determination of industrial dyes in river water. In this work, a choline chloride–decanoic acid DES facilitated rapid extraction of methyl violet under optimised conditions of pH, solvent-to-sample ratio and sonication time, yielding enrichment factors of around 20 and limits of detection in the low microgram per litre range. The green nature of the solvent and the simplicity of the procedure underscored its suitability for routine environmental monitoring.

In another development, dispersive liquid-liquid microextraction based on the solidification of a floating organic droplet (DLLME-SFOD) was adapted to DESs, enabling preconcentration of heavy metals and organic pollutants from aqueous and biological samples. By selecting DES components with melting points near ambient temperature, the floating droplet solidified upon cooling, simplifying phase separation and improving recoveries. Detailed investigations of variables such as DES composition, disperser volume and cooling time revealed enrichment factors exceeding 100 and reproducible extraction efficiencies across diverse analyte classes.

A comprehensive review of DES-based microextraction in the analysis of biological matrices has highlighted the expanding breadth of applications in clinical and pharmaceutical contexts. Over the past five years, researchers have applied DES-microextraction to blood, urine and tissue homogenates, demonstrating effective cleanup of proteins and lipids, high selectivity for small-molecule drugs, metabolites and biomarkers, and compatibility with downstream techniques such as high-performance liquid chromatography and mass spectrometry. The review emphasises the interconnection between solvent design, sample matrix properties and analytical performance, advocating for tailored DES formulations to meet the demands of specific bioanalytical challenges.

Microextraction Techniques Using Deep Eutectic Solvents publication trend

The graph below shows the total number of articles in microextraction techniques using deep eutectic solvents across all publications each year (not limited to Nature Index journals).

Technical terms

Deep eutectic solvent (DES): A low-melting mixture of hydrogen bond donors and acceptors that forms a eutectic with tunable polarity and high solvation capability.

Ultrasound-assisted liquid-liquid microextraction (UA-LLME): A technique that applies ultrasonic energy to disperse the extraction solvent into fine droplets, enhancing mass transfer and reducing extraction time.

Dispersive liquid-liquid microextraction based on solidification of floating organic droplet (DLLME-SFOD): A microextraction variant in which the extraction solvent solidifies upon cooling, facilitating easy separation of the enriched phase.

Enrichment factor: The ratio of analyte concentration in the extract to that in the original sample, indicating the degree of preconcentration achieved.

Limit of detection (LOD): The lowest concentration of an analyte that can be reliably distinguished from background noise under specified conditions.

References

1. Natural deep eutectic solvent based ultrasound assisted liquid-liquid micro-extraction method for methyl violet dye determination in contaminated river water. Water Resources and Industry (2023).
2. Deep Eutectic Solvents as Promising Green Solvents in Dispersive Liquid–Liquid Microextraction Based on Solidification of Floating Organic Droplet: Recent Applications, Challenges and Future Perspectives. Molecules (2021).
3. A review on recent applications of deep eutectic solvents in microextraction techniques for the analysis of biological matrices. Advances in Sample Preparation (2022).