Guanidinium ionic liquid-based surfactants as low cytotoxic extractants: Analytical performance in an in-situ dispersive liquid-liquid microextraction method for determining personal care products

A tool to assess analytical sample preparation procedures: Sample preparation metric of sustainability

Sample preparation is a key step in most analytical methods, generally regarded as the least green step of the entire procedure. The existing green metrics assess the greenness of sample preparation techniques through the evaluation of the whole analytical procedure: including sampling, sample preparation, and the final detection/quantitation. Such inclusion of the entire method makes assessing the sustainability of a newly developed sample preparation technique quite challenging, as many aspects not solely linked to the sample preparation step are unavoidably considered. Thus, an alternative metric that can explicitly and exclusively evaluate the sample preparation is proposed. The metric is simple; it reports the result with a clock-like diagram, displaying the greenness outcome of main sample preparation parameters and a total score. This new metric can differentiate closely related microextraction approaches in terms of sustainability. The metric is also open-source and can be used by downloading the Excel sheet provided.

Aqueous Biphasic Systems Comprising Natural Organic Acid-Derived Ionic Liquids

Despite the progress achieved by aqueous biphasic systems (ABSs) comprising ionic liquids (ILs) in extracting valuable proteins, the quest for bio-based and protein-friendly ILs continues. To address this need, this work uses natural organic acids as precursors in the synthesis of four ILs, namely tetrabutylammonium formate ([N4444][HCOO]), tetrabutylammonium acetate ([N4444][CH3COO]), tetrabutylphosphonium formate ([P4444][HCOO]), and tetrabutylphosphonium acetate ([P4444][CH3COO]). It is shown that ABSs can be prepared using all four organic acid-derived ILs paired with the salts potassium phosphate dibasic (K2HPO4) and tripotassium citrate (C6H5K3O7). According to the ABSs phase diagrams, [P4444]-based ILs outperform their ammonium congeners in their ability to undergo liquid–liquid demixing in the presence of salts due to their lower hydrogen-bond acidity. However, deviations to the Hofmeister series were detected in the salts’ effect, which may be related to the high charge density of the studied IL anions. As a proof of concept for their extraction potential, these ABSs were evaluated in extracting human transferrin, allowing extraction efficiencies of 100% and recovery yields ranging between 86 and 100%. To further disclose the molecular-level mechanisms behind the extraction of human transferrin, molecular docking studies were performed. Overall, the salting-out exerted by the salt is the main mechanism responsible for the complete extraction of human transferrin toward the IL-rich phase, whereas the recovery yield and protein-friendly nature of these systems depend on specific “IL-transferrin” interactions.

Recent Advances in Sample Preparation for Cosmetics and Personal Care Products Analysis

The use of cosmetics and personal care products is increasing worldwide. Their high matrix complexity, together with the wide range of products currently marketed under different forms imply a challenge for their analysis, most of them requiring a sample pre-treatment step before analysis. Classical sample preparation methodologies involve large amounts of organic solvents as well as multiple steps resulting in large time consumption. Therefore, in recent years, the trends have been moved towards the development of simple, sustainable, and environmentally friendly methodologies in two ways: (i) the miniaturization of conventional procedures allowing a reduction in the consumption of solvents and reagents; and (ii) the development and application of sorbent- and liquid-based microextraction technologies to obtain a high analyte enrichment, avoiding or significantly reducing the use of organic solvents. This review provides an overview of analytical methodology during the last ten years, placing special emphasis on sample preparation to analyse cosmetics and personal care products. The use of liquid–liquid and solid–liquid extraction (LLE, SLE), ultrasound-assisted extraction (UAE), solid-phase extraction (SPE), pressurized liquid extraction (PLE), matrix solid-phase extraction (MSPD), and liquid- and sorbent-based microextraction techniques will be reviewed. The most recent advances and future trends including the development of new materials and green solvents will be also addressed.

Surface-confined guanidinium ionic liquid as a new type of stationary phase for hydrophilic interaction liquid chromatography

Guanidinium-based ionic liquids possess lower toxicity and greater designability than commonly used species and have presented good performances in liquid-phase extraction and stationary phase for capillary gas chromatography. In the present work, a novel type of surface-confined guanidinium ionic liquid stationary phase was developed by bonding a hexaalkylguanidinium ionic liquid N,N,N',N'-tetramethyl-N",N"-diallylguanidinium bromide onto the surface of 3-mercaptopropyl modified silica. The obtained surface-confined guanidinium ionic liquid silica materials were characterized by elemental analysis, infrared spectroscopy and thermogravimetric analysis, and then packed as a high-performance liquid chromatography column for the evaluation of chromatographic retention behavior. Typical polar compounds were used to evaluate the separation performances, and the changes of retention with water content in mobile phase further suggested the hydrophilic interaction liquid chromatography retention mechanism. Moreover, the effect of different chromatographic factors (salt concentration, mobile phase pH, and column temperature) on retention was investigated with a series of compounds as test solutes to gain insights into the retention mechanism. The results indicated that the surface-confined guanidinium ionic liquid stationary phase exhibited a hydrophilic interaction liquid chromatography/anion-exchange mixed-mode retention behavior and possessed promising potential in separating a wide range of compounds as an alternative stationary phase for high-performance liquid chromatography.

A green miniaturized aqueous biphasic system prepared with cholinium chloride and a phosphate salt to extract and preconcentrate personal care products in wastewater samples

A miniaturized extraction/preconcentration method based on an aqueous biphasic system (μ-ABS) was developed with reagents commonly used as food additives: cholinium chloride (ChCl) as main extraction phase, K₂HPO₄ as salting-out agent, and water as the main component (being the sample for analyses). With the aim of obtaining high enrichment factors, miniaturization, and adequate analytical performance, a point in the biphasic region with the lowest amount of ChCl was selected, corresponding to 1.55% (w/w) of ChCl, 59.5% (w/w) of K₂HPO₄, and 38.95% (w/w) of water. The green μ-ABS (attending to its main elements and performance mode) was used in combination with high-performance liquid chromatography with diode-array detection (HPLC-DAD) for the determination of 9 personal care products in wastewater samples. The μ-ABS-HPLC-DAD method showed high enrichment factors (up to 100), and quantitative extraction efficiencies for those compounds containing OH groups in their structure, which can undergo hydrogen bonding with ChCl. Thus, limits of quantification down to 0.8 µg·L^-1 and extraction efficiencies between 66.4 and 108% (concentration levels of 1.3 and 13 µg·L^-1) were reached for the group of parabens and the UV-filter benzophenone-3. The method is characterized by the use of non-harmful reagents and the absence of organic solvents in the entire sample preparation procedure, while being simple, low-cost, easily compatible with HPLC, and highly efficient.

Evaluation of Structurally Different Ionic Liquid-Based Surfactants in a Green Microwave-Assisted Extraction for the Flavonoids Profile Determination of Mangifera sp. and Passiflora sp. Leaves from Canary Islands

Aqueous solutions of ionic liquids (ILs) with surface active properties were used as extraction solvents, taking advantage of their impressive solvation properties, in a green microwave-assisted solid-liquid extraction method (IL-MA-SLE) for the extraction of flavonoids from passion fruit and mango leaves. The extraction method was combined with high-performance liquid chromatography and photodiode-array detection (HPLC-PDA) and optimized by response surface methodology using the Box-Behnken experimental design. Under optimum conditions, the extraction efficiency of six structurally different IL-based surfactants was evaluated. Thus, imidazolium-, guanidinium- and pyridinium-type ILs with different tailorable characteristics, such as side chain length and multicationic core, were assessed. The decylguanidinium chloride ([C10Gu+][Cl-]) IL-based surfactant was selected as key material given its superior performance and its low cytotoxicity, for the determination of flavonoids of several samples of Passiflora sp. and Mangifera sp. leaves from the Canary Islands, and using as target analytes: rutin, quercetin and apigenin. The analysis of 50 mg of plant material only required 525 µL of the low cytotoxic IL-based surfactant solution at 930 mM, 10.5 min of microwave irradiation at 30 °C and 50 W, which involves a simpler, faster, more efficient and greener method in comparison with other strategies reported in the literature for obtaining bioactive compounds profiles from plants.

Sustainable Micro-Scale Extraction of Bioactive Phenolic Compounds from Vitis vinifera Leaves with Ionic Liquid-Based Surfactants

This paper proposes a new sustainable and simple strategy for the micro-scale extraction of phenolic compounds from grapevine leaves with analytical purpose. The method is based on a microwave-assisted solid-liquid extraction approach (MA-SLE), using an aqueous solution of an ionic liquid (IL)-based surfactant as extraction phase. The method does not require organic solvents, nor any clean-up step, apart from filtration prior to the injection in the analytical system. Two IL-based surfactants were evaluated, and the method was optimized by using experimental designs, resulting in the use of small amounts of sample (100 mg) and extraction phase (2.25 mL), low concentrations of the selected 1-hexadecyl-3-butyl imidazolium bromide IL (0.1 mM), and 30 min of extraction time. The proposed methodology was applied for the determination of the polyphenolic pattern of six different varieties of Vitis vinifera leaves from the Canary Islands, using high-performance liquid chromatography and photodiode array detection for the quantification of the compounds. The proposed MA-SLE approach was greener, simpler, and more effective than other methods, while the results from the analysis of the leaves samples demonstrate that these by-products can be exploited as a source of natural compounds for many applications.

Relationship between the Structure of Ionic Liquid and Its Enrichment Ability To Trace Fungicides from an Environmental Water Sample

To elucidate the relationship between the structure of ionic liquid (IL) and its enrichment ability to trace pesticides from an environmental water sample, a series of imidazole-based ILs were synthesized to extract four fungicides (boscalid, cyprodinil, fluazinam, and pyrimethanil) through an in situ ionic liquid dispersive liquid-liquid microextraction method. The results showed that aromatic heterocyclic monocation ionic liquids (MILs) had better extraction ability to fungicides than other three alicyclic heterocyclic MILs. Dication ionic liquids (DILs) with the four carbons at the side chain had better ability to extract fungicides than MILs, and DILs with a long bridge carbon chain had better recoveries of fungicides with low K_ow values. The proposed method showed high mean enrichment factors and high recoveries of the fungicides from real water samples. The rules of the relationship between the structure of IL and enrichment ability are instructive to the application of ILs in pretreatment of complex substances.

Recent advances on ionic liquid uses in separation techniques

The molten organic salts with melting point below 100°C, commonly called ionic liquids (ILs) have found numerous uses in separation sciences due to their exceptional properties as non molecular solvents, namely, a negligible vapor pressure, a high thermal stability, and unique solvating properties due to polarity and their ionic character of molten salts. Other properties, such as viscosity, boiling point, water solubility, and electrochemical window, are adjustable playing with which anion is associated with which cation. This review focuses on recent development of the uses of ILs in separation techniques actualizing our 2008 article (same authors, J. Chromatogr. A, 1184 (2008) 6-18) focusing on alkyl methylimidazolium salts. These developments include the use of ILs in nuclear waste reprocessing, highly thermally stable ILs that allowed for the introduction of polar gas chromatography capillary columns able to work at temperature never seen before (passing 300°C), the use of ILs in liquid chromatography and capillary electrophoresis, and the introduction of tailor-made ILs for mass spectrometry detection of trace anions at the few femtogram level. The recently introduced deep eutectic solvents are not exactly ILs, they are related enough so that their properties and uses in countercurrent chromatography are presented.