Elsevier

Microchemical Journal

Volume 170, November 2021, 106750
Microchemical Journal

Review Article
Homogenous liquid-liquid micro-extraction of pollutants in complex matrices

https://doi.org/10.1016/j.microc.2021.106750Get rights and content

Highlights

  • Pollutants can be extracted using homogenous liquid-liquid micro-extraction (HLLME)

  • Ionic liquids, switchable solvents and DES are good extractants during HLLME.

  • Floatation-based HLLME renders centrifugation unnecessary.

  • Hyphenated HLLME techniques produce cleaner chromatograms.

Abstract

Homogenous liquid-liquid micro-extraction (HLLME) is a pre-concentration technique for pollutants in complex matrices. Researchers have used different modes of HLLME during sample pre-treatment. Switchable solvent-based HLLME mode have been successfully used by some researchers during pollutant pre-concentration while others have used modes based on other emerging solvents such as deep eutectic solvents and ionic liquids for the pre-concentration of different types of pollutants in food and environmental samples. On the other hand, some researchers have managed to by-pass the time-consuming and tedious centrifugation step during pre-concentration of pollutants by using the floatation-based mode of HLLME. This paper explores the recent applications of these modes of HLLME as pollutant pre-concentration techniques. In addition, the paper gives an outline of the challenges associated with the use of HLLME as well as the future prospects of the technique.

Introduction

Environmental contamination by organic and inorganic pollutants has received superior attention from researchers due to their toxic nature [1], [2], [3], [4]. These pollutants have negative impacts to the environment. Long-term exposure to these organic and inorganic pollutants can cause asthma, decreased cardiac output, heart and lung diseases, and allergic reactions [5], [6], [7], [8]. Thus, it is critically important to determine their concentrations in food and environmental samples. Close monitoring of these pollutants would enable corrective measures to be taken before their concentrations exceed the maximum allowable limits in food and environmental sample.

There are many analytical techniques that can be employed to monitor organic and inorganic pollutants in food and environmental samples. These include the adsorptive removal of the pollutants using adsorbents such as optical composite materials [9] and functionalised composite materials [10] as well as electrochemical detection [11], [12] and the use of sensors [13]. In addition, chromatographic techniques such as gas chromatography [14], [15], [16], supercritical chromatography [17], [18], [19], micellar electrokinetic chromatography [20], [21], [22] and high performance liquid chromatography [23], [24], [25] can be used during analysis of pollutants. Spectroscopic techniques such as inductively coupled plasma-mass spectroscopy [26], [27], [28] and atomic absorption spectroscopy [29], [30], [31] are also useful for the analysis of pollutants in complex matrices. Analysis of organic and inorganic pollutants using these techniques is very effective if their concentrations are above the instrument’s limits of detection and quantification. The contaminants in food and environmental samples, however, are usually found in trace concentrations. Thus, it is difficult to directly analyse trace amounts of pollutants by instrumental methods since their concentrations will be usually lower than the limits of detection of the analytical instruments. For these reasons, the use of pre-concentration methods prior to instrumental analysis becomes an imperative to cause improvement of sensitivity as well as for the enhancement of selectivity during their detection.

Pollutants in food and environmental samples can be pre-concentrated using traditional methods such as liquid-liquid extraction [32], [33] and solid-phase extraction [34], [35]. These traditional pre-concentration techniques use large amounts of toxic organic solvents and have a long extraction time. In addition, these traditional pre-concentration techniques are usually associated with the production of large amounts of secondary wastes [36], [37], [38]. As a result, the attention of most researchers is now focused on miniaturised pre-concentration techniques. Among these we have miniaturised sorbent-based techniques such as QuEChERS [39], [40], solid phase micro-extraction [41], [42] and stir bar soptive extraction. They are eco-friendly since they use very small amounts of organic solvents, and they are sometimes solvent-free. In addition, they are highly selective, especially when composites with tailor-made functionalities are used as adsorbents. However, fabrication of some these functionalised composite adsorbents occur for long periods at elevated temperatures risking pollution of the environment by toxic by-products. Alternatively, liquid phase micro-extraction (LPME) techniques such as single-drop micro-extraction [43], hollow fibre liquid-phase micro-extraction [2], [44], [45], [46], dispersive liquid–liquid micro-extraction [47], [48], [49], [50] and homogeneous liquid–liquid micro-extraction (HLLME) [51], [52], [53] can be used. These LPME techniques have an edge over the traditional methods since they use lower volumes of organic solvents, low operation cost and they have relatively higher extraction recoveries.

DLLME and HLLME are closely related pre-concentration techniques. The DLLME technique is, however, widely used by researchers as compared to HLLME [1], [54], [55]. It is based on the use of a ternary solvent system composed of aqueous sample, a disperser and extraction solvent (the disperser and extraction solvents are usually organic) [54], [56]. Its use during pre-concentration depends on the availability of an extraction solvent with a high affinity of the analyte, low solubility in water, and can form tiny droplets in the disperser solvent [47], [57]. The advantages of DLLME include that it uses less organic solvents, short extraction time, high enrichment factors and less operation cost. One of its limitations, however, is that it uses two different organic solvents and is, therefore, bound to cause relatively high pollution of environments from solvents [57], [58]. A variant of DLLME, HLLME can be used to minimise this problem since it uses a binary solvent system (aqueous sample and extraction solvent). Thus, it causes less pollution of the environment by solvents as compared to DLLME. Its choice during pre-concentration of pollutants depends on the availability of an extraction solvent whose hydrophilicity can be easily changed by an external trigger such as pH or temperature changes.

HLLME is a relatively simple, fast and efficient sample pre-concentration technique [59]. Some researchers have successfully used it to pre-concentrate contaminants in complex matrices (Fig. 1). It involves the extraction of the desired analyte, existing in the homogeneous aqueous solution, into the water-immiscible sediment phase. The initial condition during this pre-concentration technique is a homogeneous solution, where there is no interface between the water phase and the extraction solvent phase. Consequently, it has the advantage of extremely fast extraction speed due to the absence of obstacles from the surface contact between the aqueous phase and the organic phase during the extraction procedure.

The efficiency of the HLLME during pre-concentration of pollutant residues largely hinges on the proper choice of the extraction solvents. The solvent used as the extractant should have functionalities that will enable it to form strong interactions with target pollutant. During conventional HLLME, organic solvents are usually used as extraction solvents [59], [60]. The use of organic solvents, however, is not very appealing from an environmental point of view since most of them are toxic to living organism. Thus, some researchers are now replacing organic solvents with emerging green solvents such as ionic liquids [61], switchable solvents [51] and deep eutectic solvents (DES) [62] during HLLME pre-concentration of pollutants in food and environmental samples. Centrifugation is usually used to cause phase separation during HLLME and other pre-concentration techniques. However, this time-consuming step can be by-passed by using air floatation to cause phase separation during HLLME [63], [64].

This paper explores the application of HLLME during the pre-concentration of pollutants in complex matrices. Special emphasis is placed on the use of emerging green solvents such as ionic liquids, switchable solvents and DESs during the HLLME methods. In addition, the application air floatation to cause phase separation during HLLME is treated in detail in this paper. To the best our knowledge, this is going to be among the first papers to give a detailed review of the application of HLLME during pollutant pre-concentration in food and environmental samples. This is going to be an informative paper to those in the food industry as they engage in quality control as well as the agricultural sector since HLLME is a green pre-concentration technique that can be very useful during monitoring of agro-chemicals in the environment.

Section snippets

Deep eutectic solvent-based HLLME

Deep eutectic solvents (DESs) are eutectic mixtures of two or three non-toxic, biodegradable components that can form intermolecular hydrogen bonds between them [65], [66], [67]. The mixture should be composed of hydrogen bond donors and hydrogen bond acceptors, which interact resulting in the formation of a eutectic mixture, with a melting point that is lower than the components mixed [68], [69]. Depending on the components used during synthesis, DESs can be either hydrophilic or hydrophobic

Challenges and future prospects

HLLME is a sensitive and effective technique for the pre-concentration of pollutants in food and environmental samples. Its use, however, is not free of challenges. The challenges encountered during the HLLME technique are usually associated with the solvents used for the extraction of the pollutant residues in complex matrices. Organic solvents are usually used during conventional HLLME techniques as extractants [52], [59], [80]. The use of organic solvents poses a serious environmental

Conclusion

HLLME is a relatively fast, simple and cost-effective technique for the pre-concentration of trace amounts of pollutants in food and environmental samples. It uses very small amounts of solvents that can be easily recovered after the pre-concentration procedure. The environmental footprint of HLLME can be reduced by replacement of toxic organic solvents with emerging green solvents such switchable solvents, ionic liquids and DES during the pre-concentration of pollutants in complex matrices.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

Authors are grateful to the Research centre, University of Venda, for financial support.

References (118)

  • Y. Liu et al.

    Analysis of fluorinated compounds by micellar electrokinetic chromatography-mass spectrometry

    J. Chromatogr. A.

    (2021)
  • B. Pasquini et al.

    Analytical quality by design in the development of a solvent-modified micellar electrokinetic chromatography method for the determination of sitagliptin and its related compounds

    J. Pharm. Biomed. Anal.

    (2021)
  • K. Zemankova et al.

    Micellar electrokinetic chromatography as a powerful analytical tool for research on prebiotic chemistry

    Microchem. J.

    (2021)
  • M.L. Astolfi et al.

    An optimized method for sample preparation and elemental analysis of extra-virgin olive oil by inductively coupled plasma mass spectrometry

    Food Chem.

    (2021)
  • S. Kara et al.

    Arsenic speciation in rice samples for trace level determination by high performance liquid chromatography-inductively coupled plasma-mass spectrometry

    Food Chem.

    (2021)
  • H. Zhang et al.

    Discrimination of geographical origin and species of China’s cattle bones based on multi-element analyses by inductively coupled plasma mass spectrometry

    Food Chem.

    (2021)
  • L.F.R. Lemes et al.

    Combination of supramolecular solvent-based micro-extraction and ultrasound-assisted extraction for cadmium determination in flaxseed flour by thermospray flame furnace atomic absorption spectrometry

    Food Chem.

    (2021)
  • M. Mehrabian et al.

    Preparation and application of Fe3O4@ SiO2@poly(o-phenylenediamine) nanoparticles as a novel magnetic sorbent for the solid-phase extraction of tellurium in water samples and its determination by ET-AAS

    Microchem. J.

    (2021)
  • J. Milheiro et al.

    An accurate single-step LLE method using keeper solvent for quantification of trace amounts of sotolon in Port and white table wines by HPLC-DAD

    Food Chem.

    (2021)
  • L.J. Ney et al.

    Chloroform-based liquid-liquid extraction and LC-MS/MS quantification of endocannabinoids, cortisol and progesterone in human hair

    J. Pharm. Biomed. Anal.

    (2021)
  • B. Hatamluyi et al.

    Improved solid phase extraction for selective and efficient quantification of sunset yellow in different food samples using a novel molecularly imprinted polymer reinforced by Fe3O4@UiO-66-NH2

    Food Chem.

    (2021)
  • H. Tazoe et al.

    Determination of Nd isotopic composition in seawater using newly developed solid phase extraction and MC-ICP-MS

    Talanta.

    (2021)
  • X. Dong et al.

    A novel dispersive magnetic solid phase micro-extraction using ionic liquid-coated amino silanized magnetic graphene oxide nanocomposite for high efficient separation/pre-concentration of toxic ions from shellfish samples

    Food Chem.

    (2021)
  • C.I. Kosma et al.

    Accurate mass screening of pesticide residues in wine by modified QuEChERS and LC-hybrid LTQ/Orbitrap-MS

    Food Chem.

    (2021)
  • X. Zang et al.

    Solid-phase micro-extraction of eleven organochlorine pesticides from fruit and vegetable samples by a coated fiber with boron nitride modified multi-walled carbon nanotubes

    Food Chem.

    (2021)
  • J.M. González-Jartín et al.

    Multi-analyte method for the determination of regulated, emerging and modified mycotoxins in milk: QuEChERS extraction followed by UHPLC–MS/MS analysis

    Food Chem.

    (2021)
  • X. Theurillat et al.

    A multi-residue pesticide determination in fatty food commodities by modified QuEChERS approach and gas chromatography-tandem mass spectrometry

    Food Chem.

    (2021)
  • W. Zhang et al.

    HS-SPME and GC/MS volatile component analysis of Yinghong No. 9 dark tea during the pile fermentation process

    Food Chem.

    (2021)
  • V. Hrdlička et al.

    Differential pulse voltammetric determination of homovanillic acid as a tumor biomarker in human urine after hollow fiber-based liquid-phase micro-extraction

    Talanta.

    (2021)
  • I. Kraševec et al.

    Determination of polar benzotriazoles in aqueous environmental samples by hollow-fibre micro-extraction method with LC-MS/MS and its comparison to a conventional solid-phase extraction method

    Microchem. J.

    (2021)
  • N.N. Nia et al.

    Amino acids- based hydrophobic natural deep eutectic solvents as a green acceptor phase in two-phase hollow fiber-liquid micro-extraction for the determination of caffeic acid in coffee, green tea, and tomato samples

    Microchem. J.

    (2021)
  • M.F. Fernández et al.

    Determination of bisphenols, parabens, and benzophenones in placenta by dispersive liquid-liquid micro-extraction and gas chromatography-tandem mass spectrometry

    Chemosphere.

    (2021)
  • H. Musarurwa et al.

    Deep eutectic solvent-based dispersive liquid-liquid micro-extraction of pesticides in food samples

    Food Chem.

    (2021)
  • C. Ortega-Zamora et al.

    Extraction of phthalic acid esters from soft drinks and infusions by dispersive liquid-liquid micro-extraction based on the solidification of the floating organic drop using a menthol-based natural deep eutectic solvent

    J. Chromatogr. A.

    (2021)
  • Y. Xu et al.

    Application of the liquid-liquid dispersed micro-extraction based on phase transition behavior of temperature sensitive polymer to rapidly detect 5 BPs in food packaging

    Food Chem.

    (2021)
  • M. Nazraz et al.

    Deep eutectic solvent dependent carbon dioxide switching as a homogeneous extracting solvent in liquid-liquid micro-extraction

    J. Chromatogr. A.

    (2021)
  • A. Luiz Oenning et al.

    A green and low-cost method employing switchable hydrophilicity solvent for the simultaneous determination of antidepressants in human urine by gas chromatography - mass spectrometry detection

    J. Chromatogr. B-Anal. Technol. Biomed. Life Sci.

    (2020)
  • E. Ragheb et al.

    Magnetic solid-phase extraction using metal-organic framework-based biosorbent followed by ligandless deep-eutectic solvent-ultrasounds-assisted dispersive liquid-liquid micro-extraction (DES-USA-DLLME) for pre-concentration of mercury (II)

    Microchem. J.

    (2021)
  • M. Behpour et al.

    Combination of gel-electromembrane extraction with switchable hydrophilicity solvent-based homogeneous liquid-liquid micro-extraction followed by gas chromatography for the extraction and determination of antidepressants in human serum, breast milk and wastewater

    J. Chromatogr. A.

    (2020)
  • Z. Wang et al.

    Microwave-assisted ionic liquid homogeneous liquid–liquid micro-extraction coupled with high performance liquid chromatography for the determination of anthraquinones in Rheum palmatum L

    J. Pharm. Biomed. Anal.

    (2016)
  • W. Ma et al.

    pH-induced deep eutectic solvents based homogeneous liquid-liquid micro-extraction for the extraction of two antibiotics from environmental water

    Microchem. J.

    (2021)
  • H. Cheng et al.

    Applications of deep eutectic solvents for hard-to-separate liquid systems

    Sep. Purif. Technol.

    (2021)
  • Q. Dong et al.

    Efficient removal of ginkgolic acids from Ginkgo biloba leaves crude extract by using hydrophobic deep eutectic solvents

    Ind. Crops Prod.

    (2021)
  • T.K. Rye et al.

    Electromembrane extraction of peptides using deep eutectic solvents as liquid membrane

    Anal. Chim. Acta.

    (2021)
  • W. Deng et al.

    A density-tunable liquid-phase micro-extraction system based on deep eutectic solvents for the determination of polycyclic aromatic hydrocarbons in tea, medicinal herbs and liquid foods

    Food Chem.

    (2021)
  • A. Elik et al.

    Ionic hydrophobic deep eutectic solvents in developing air-assisted liquid-phase micro-extraction based on experimental design: Application to flame atomic absorption spectrometry determination of cobalt in liquid and solid samples

    Food Chem.

    (2021)
  • P. Janicka et al.

    Novel “acid tuned” deep eutectic solvents based on protonated L-proline

    J. Mol. Liq.

    (2021)
  • A. Shishov et al.

    An automated homogeneous liquid-liquid micro-extraction based on deep eutectic solvent for the HPLC-UV determination of caffeine in beverages

    Microchem. J.

    (2019)
  • X. Di et al.

    Dispersive micro-solid phase extraction combined with switchable hydrophilicity solvent-based homogeneous liquid-liquid micro-extraction for enrichment of non-steroidal anti-inflammatory drugs in environmental water samples

    J. Chromatogr. A.

    (2020)
  • T. Amini et al.

    Pre-concentration and GC-MS determination of caffeine in tea and coffee using homogeneous liquid–liquid micro-extraction based on solvents volume ratio alteration

    J. Chromatogr. B.

    (2018)
  • Cited by (0)

    View full text