Sustainable Green Solvents in Microextraction Techniques
Introduction
A typical analytical procedure consists of three main parts: sampling, sample preparation, and analysis. Sample preparation based on extraction techniques plays a crucial role in the entire analytical process, as it ensures accurate and reliable analysis of analytes by eliminating matrix interferences. In addition, in recent years, with the continuous development of green chemistry (Green chemistry was originally mainly driven by organic synthetic approaches), green analytical chemistry is slowly following, searching for ways to reduce volumes, cost and toxicity of analytically used chemicals and lowering energy usage. Thus, microextraction techniques with the advantageous in terms of low cost, minimal solvent usage, reduced energy consumption, and waste generation have been pursued as novel promising methods for sample preparation. However, these are not enough to achieve real green analytical chemistry, the replacement of hazardous and toxic solvents by sustainable green solvents is indispensable to achieve green analytical chemistry in microextraction techniques, which represents a promising trend. In this regard, Alfa Chemistry provides a concise summary of recent advances in the prominent sustainable green solvents utilized in microextraction techniques according to recent report [1].
Sustainable Green Solvents In Microextraction
Over the past two decades, emerging sustainable green solvents, including ionic liquids (ILs), deep eutectic solvents (DESs), natural deep eutectic solvents (NADESs), amphiphilic solvents, supercritical fluids (SCFs), switchable solvents (SSs) and bio-solvents, have garnered great attention as extraction solvents, fulfilling of many criteria of green analytical chemistry.
- Ionic liquids (ILs): ILs are generally formed from large asymmetrical organic cations, combined with inorganic or organic anions. Owing to their tunable physicochemical properties and the advantages of no pollution, easy to separate and recover and recycling, ILs have been extensively utilized as effective green extraction solvents. At present, novel IL derivatives, such as room-temperature ionic liquids (RTILs), polymeric ionic liquids (PILs), magnetic ionic liquids (MILs), and switchable ionic liquids (SILs), have gained significant attention for their use in microextraction.
- Eutectic mixtures (DESs and NADESs): To address the issues of biodegradability and high cost of ILs, DESs are formed by simply mixing a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD). In addition to the similar solvent characteristics, DESs offer several advantages over ILs, including the 100 % atom economy, low cost, and low toxicity. NADESs, a sub-class of DESs developed in 2011, are exclusively from natural components. Natural organic acids (e.g., oxalic acid) and carbohydrates (e.g., glucose) are employed as HBDs in the preparation of NADESs, while choline chlorides still serve as HBAs. Nowadays, ILs and eutectic mixtures account for more than half of the current sustainable green extraction solvents for microextraction, due to their unique characteristics, tailorable features, and high solvation power.
Fig. 1. Most common components used for preparation of DESs and NADESs.
- Amphiphilic solvents: Amphiphilic solvents have both hydrophobic heads and hydrophilic tails in a molecule. They are increasingly recognized as sustainable and environmentally friendly alternatives due to their low toxicity, renewability, efficiency, and versatility in microextraction processes. And the amphiphilic solvents in microextraction include surfactants, biosurfactants (synthesized from natural feed stocks), and nanostructured and amphiphilic supramolecular solvent (SUPRAS) (it is developed and formed by sequential self-assembly and coacervation of amphiphiles dispersed in a continuous phase). Thereinto, microextraction by surfactants has become a flexible and efficient sample preparation method in various industries such as petroleum, food, cosmetics, agriculture, and environment, and biosurfactants have been successfully employed in the microextraction of heavy metals and bioactive molecules.
Fig. 2. Schematic of the SUPRAS-based microextraction process.
- Supercritical fluids (SCFs): SCFs are green solvents that exhibit gas-like viscosity with faster mass transfer and liquid-like density with good fluid solvency during extraction, when the conditions exceed their values of critical temperature (TCT) and critical pressure (PCP). Supercritical CO2 is the most commonly used SCF in microextraction due to its innocuousness, sustainability, low cost, abundance, and easy removal from the final product by depressurization, as well as its low critical temperature and inert properties. It is crucial for the extraction of bioactive and oxygen-sensitive compounds.
Fig. 3. Schematic representation of a typical supercritical CO2 extraction process.
- Switchable solvents (SSs): SSs have unique ability to rapidly and reversibly switch between two opposite conformations with different physicochemical properties, under atmospheric pressure (1 bar), which allow them to be easily separated without the need of additional equipment and solvent separation methods such as distillation, evaporation or stripping method. In addition, they are greenness, speed, simplicity, repeatability, and low cost. Thus, SSs have been widely applied in both large- and small-scale extractions.
- Bio-based solvents: Bio-based solvents are derived from a wide variety of renewable biomass sources, including plants, animals, microbes, and agricultural waste. These solvents are abundant in resources, biodegradable, and easy to recycle, thereby reducing environmental impacts and providing satisfactory toxicology assessment results. To date, several bio-based solvents such as ethanol, glycerol, cyclopentyl, methyl ether, d-limonene, γ-valerolactone, and 2-methyltetrahydrofuran, as well as natural products such as biodiesel and vegetable oils have been used for efficiency in extracting compounds of interest from various matrices.
Fig. 4. Panoramic view of bio-based solvents.
Alfa Chemistry is a global leading supplier of analytical chemistry reagents. We provide a wide range of high quality solvents including sustainable green solvents, and many other analytical chemistry products. If you cannot find the suitable products, Alfa Chemistry also offers you with custom synthesis service. If necessary, please don't hesitate to contact us.
Reference
- Zhang Y., et al. Recent advances in microextraction techniques using sustainable green solvents for mass spectrometry analysis[J]. TrAC Trends in Analytical Chemistry, 2023: 117412.
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