Dispersive Liquid-Liquid Microextraction: A Review and Roundup of Green Sample Prep Advancements

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The still relatively new technique has distinct advantages, but a few of those benefits make it incompatible with some of the currently accepted principles of green sample preparation.

Research recently published in the journal TrAC, Trends in Analytical Chemistry examines the advantages and pitfalls of dispersive liquid-liquid microextraction (dLLME), and reviews recent innovations designed to better align dLLME with green analytical sample preparation principles (1). The journal article was written by Hakim Faraji, who since 2022 has been a researcher at the University of La Laguna, located on the island of Tenerife, Spain.

Central Campus is one of five campuses of University of La Laguna (Universidad de La Laguna). Laguna University - oldest in Canary Islands. San Cristobal de La Laguna, Tenerife, Canary Islands, Spain. | Image Credit: © dbrnjhrj - stock.adobe.com

Central Campus is one of five campuses of University of La Laguna (Universidad de La Laguna). Laguna University - oldest in Canary Islands. San Cristobal de La Laguna, Tenerife, Canary Islands, Spain. | Image Credit: © dbrnjhrj - stock.adobe.com

Dispersive liquid-liquid microextraction, as defined by Faraji, was developed nearly two decades ago as a miniaturization of traditional liquid-liquid extraction (LLE). Summarized on a basic level, a mixture comprised of an extraction solvent and a dispersive solvent is rapidly injected into a sample, creating a resultant turbid solution that contains fine droplets of the extraction solvent, which are then centrifuged to integrate and unify them prior to collection by a micro-syringe for analysis (1). The technique’s popularity since its introduction, Faraji said, has been attributed to a combination of multiple factors including simplicity, affordability, low solvent consumption volume and high efficiency.

Li Hsin Tseng and colleagues have previously demonstrated the efficacy of dLLME in real-world applications such as highly sensitive determination of barbiturates in fluids produced by humans, as recounted in a 2023 study in the Journal of Separation Science (2).

However, the technique’s typical use of chlorinated extracting solvents, plus the requirement of a second solvent for dispersion and a centrifugation step—not to mention difficulties collecting the extractant after phase separation—make it not only challenging to automate, but altogether incompatible with some of the principles of green sample preparation (GSP) (1). It is here where Faraji’s paper reviews some of the previous literature on the dichotomy between these two areas and attempts to suggest ways to harmonize them.

On the topic of dispersion, Faraji suggests multiple innovative strategies: the use of magnetic nanoparticles, vortex, and ultrasound techniques, all meant to simplify the process of dLLME and cut back on the need for additional solvents (1). Centrifugation, he goes on to say, can be time-consuming, and so he recommends procedures such as salting-out or gas stream flotation to streamline the process and encourage the deployment of automation. For extractant collection, which Faraji said has been a “persistent challenge” in dLLME, simplifications have emerged in the form of certain solvent properties and advanced gas stream techniques.

Yet despite all these tweaks and adjustments to the dLLME process, Faraji highlights one goal first and foremost: to develop sustainable solvents that have safe synthesis processes, while also providing superior extraction efficiency (1). Reducing the viscosity of these solvents, he said, could be an even more helpful step. Considering all these changes could result in the future successful commercialization of dispersive liquid-liquid microextraction for on-site analysis, and moreover, a meaningful advancement in the field of analytical chemistry at large.

References

(1) Faraji, H. Advancements in Overcoming Challenges in Dispersive Liquid-Liquid Microextraction: An Overview of Advanced Strategies. TrAC, Trends Anal. Chem. 2024, 170, 117429. DOI: 10.1016/j.trac.2023.117429

(2) Advanced Microextraction Technique Enhances Barbiturate Detection in Serum Samples. LCGC. MJH Life Sciences, 2023. https://www.chromatographyonline.com/view/advanced-microextraction-technique-barbiturate-detection-serum-samples (accessed 2024-05-14).