Imidazolium-based ionic liquid surfactants as pseudostationary in combination with a chiral selector in micellar electrokinetic chromatography

Comparison of aqueous and non-aqueous capillary electrophoresis for the determination of four benzalkonium chloride homologues in compound chemical disinfectants

A new method was established for the simultaneous analysis of four homologous benzalkonium chlorides (dodecyldimethylbenzyl ammonium chloride, tetradecyldimethylbenzyl ammonium chloride, hexadecyldimethylbenzyl ammonium chloride, and octadecyldimethylbenzyl ammonium chloride) in compound chemical disinfectants using non-aqueous capillary electrophoresis (CE) based on a micellar electrokinetic chromatography mode with direct ultraviolet detection. The separation was performed on an uncoated fused quartz capillary with a total length of 60.2 cm and a diameter of 25 μm. The separation buffer consisted of a mixture of methanol/acetonitrile (60:40, v/v) containing 70 mmol/L sodium acetate, 60 mmol/L trifluoroacetic acid and 20 mmol/L sodium dodecyl sulfate. The sample buffer was a methanol solution containing only 2 mmol/L trifluoroacetic acid. The separation voltage was set at 8 kV with a working current of approximately 2.3 μA. The detection wavelength was 214 nm. Under optimal conditions, the limit of detection and limit of quantification for these four benzalkonium chlorides (BACs) were 1.0 mg/L and 5.0 mg/L, respectively. Good linearities were observed in the concentration ranges from 5.0 to 100.0 mg/L, with correlation coefficients above 0.999 for all compounds. The recoveries of these four BACs ranged from 92.5 % to 109.1 % with relative standard deviations below 4.7 %. With the new method, all four BACs could be analyzed in a single injection. In contrast, the aqueous CE method in the National Standard GB/T 26369-2020 only allowed for the simultaneous analysis of the first three homologous. The new method demonstrated the improved peak shape compared to the aqueous CE method and then was successfully applied to the analysis of 19 commercially available samples, such as object table disinfectants, hand sanitizers, and disinfectant wipes, which claimed to contain quaternary ammonium compound. The results obtained using the new method were compared with those of the aqueous CE of the National Standard Method, and no statistically significant differences were observed. The new method is simple in pre-treatment and provides accurate results, making it highly suitable for routine analysis.

From capillaries to microchips, green electrophoretic features for enantiomeric separations: A decade review (2013-2022)

Enantioseparation by the electromigration-based method is well-established and widely discussed in the literature. Electrophoretic strategies have been used to baseline resolve complex enantiomeric mixtures, typically using a selector substance into the background electrolyte (BGE) from capillaries to microchips. Along with developing new materials/substances for enantioseparations, it is the concern about the green analytical chemistry (GAC) principles for method development and application. This review article brings a last decade's update on the publications involving enantioseparation by electrophoresis for capillary and microchip systems. It also brings a critical discussion on GAC principles and new green metrics in the context of developing an enantioseparation method. Chemical and green features of native and modified cyclodextrins are discussed. Still, given the employment of greener substances, ionic liquids and deep-eutectic solvents are highlighted, and some new selectors are proposed. For all the mentioned selectors, green features about their production, application, and disposal are considered. Sample preparation and BGE composition in GAC perspective, as well as greener derivatization possibilities, were also addressed. Therefore, one of the goals of this review is to aid the electrophoretic researchers to look where they have not.

Recent development of chiral ionic liquids for enantioseparation in liquid chromatography and capillary electrophoresis: A review

Ionic liquids (ILs), which are salts in a molten state below 100 °C, have become a hot topic of research in various fields because of their negligible vapour pressure, high thermal stability, and tunable viscosity. Chiral ionic liquids (CILs) can be applied in chromatography and capillary electrophoresis fields to improve the performance of enantiomeric separation, such as chiral stationary phases (CSPs) and mobile phase additives in high-performance liquid chromatography (HPLC); CSPs in gas chromatography (GC); and background electrolyte additives (BGE), chiral ligands and chiral selectors (CSs) in capillary electrophoresis (CE). This review focuses on the applications of CILs in HPLC and CE for the separation of enantiomers in the past five years. The mechanism for separating enantiomers was explained, and the prospect of the application of CILs in chiral liquid chromatography (LC) and CE analysis was also discussed.

Evaluating the hazardous impact of ionic liquids - Challenges and opportunities

Ionic liquids (ILs), being related to the design of new environmentally friendly solvents, are widely considered for applications within the "green chemistry" concept. Due to their unique properties and wide diversity, ILs allow tailoring new separation procedures and producing new materials for advanced applications. However, despite the promising technical performance, environmental concerns highlighted in recent studies focused on the toxicity and biodegradability of ILs and their metabolites have revealed that ILs safety labels are not as benign as previously claimed. This review refers to the fundamentals about the properties and applications of ILs also in the context of their potential environmental effect. Toxicological issues and harmful effects related to the use of ILs are discussed, including the evaluation of their biodegradability and ecological impact on diverse organisms and ecosystems, also with respect to bacteria, fungi, and cell cultures. In addition, this review covers the tools used to assess the toxicity of ILs, including the predictive computational models and the results of studies involving cell membrane models and molecular simulations. Summing up the knowledge available so far, there are still no reliable criteria for unequivocal attribution of toxicity and environmental impact credentials for ILs, which is a challenging research task.

Past, present, and future developments in enantioselective analysis using capillary electromigration techniques

Enantioseparation of chiral products has become increasingly important in a large diversity of academic and industrial applications. The separation of chiral compounds is inherently challenging and thus requires a suitable analytical technique that can achieve high resolution and sensitivity. In this context, CE has shown remarkable results so far. Chiral CE offers an orthogonal enantioselectivity and is typically considered less costly than chromatographic techniques, since only minute amounts of chiral selectors are needed. Several CE approaches have been developed for chiral analysis, including chiral EKC and chiral CEC. Enantioseparations by EKC benefit from the wide variety of possible pseudostationary phases that can be employed. Chiral CEC, on the other hand, combines chromatographic separation principles with the bulk fluid movement of CE, benefitting from reduced band broadening as compared to pressure-driven systems. Although UV detection is conventionally used for these approaches, MS can also be considered. CE-MS represents a promising alternative due to the increased sensitivity and selectivity, enabling the chiral analysis of complex samples. The potential contamination of the MS ion source in EKC-MS can be overcome using partial-filling and counter-migration techniques. However, chiral analysis using monolithic and open-tubular CEC-MS awaits additional method validation and a dedicated commercial interface. Further efforts in chiral CE are expected toward the improvement of existing techniques, the development of novel pseudostationary phases, and establishing the use of chiral ionic liquids, molecular imprinted polymers, and metal-organic frameworks. These developments will certainly foster the adoption of CE(-MS) as a well-established technique in routine chiral analysis.

Ionic liquids in electrokinetic chromatography

There is an interest in the application of ionic liquids as additives into the separation media to improve achiral and chiral separations in electrokinetic chromatography (EKC). This review will critically discuss the developments on the use of ionic liquids in the different modes of EKC during the last five years (2015-mid 2020). A healthy number of 48 research articles searched through Scopus were categorised into two: ionic liquids as sole pseudophase (micelles, microemulsions, ligand exchange pseudophase or molecular pseudophase) and ionic liquids with pseudophase (achiral or chiral). More than half of the papers dealt with chiral separations that were mostly facilitated by another additive or pseudophase. The role of ionic liquids for improvement of separations were analysed, and we provided some recommendations for further investigations. Finally, the use of ionic liquids in different on-line sample concentration or stacking methods (i.e., field enhancement and sweeping) was briefly discussed.

Chiral Micellar Electrokinetic Chromatography

The potential of Micellar Electrokinetic Chromatography to achieve enantiomeric separations is reviewed in this article. The separation principles and the most frequently employed separation strategies to achieve chiral separations by Micellar Electrokinetic Chromatography are described. The use of chiral micellar systems alone or combined with other micellar systems or chiral selectors, as well as of mixtures of achiral micellar systems with chiral selectors is discussed together with the effect of different additives present in the separation medium. Indirect methods based on the derivatization of analytes with chiral derivatizing reagents and the use of achiral micelles are also considered. Preconcentration techniques employed to improve sensitivity and the main approaches developed to facilitate the coupling with Mass Spectrometry are included. The most recent and relevant methodologies developed by chiral Micellar Electrokinetic Chromatography and their applications in different fields are presented.

Recent advances in the enantioseparation promoted by ionic liquids and their resolution mechanisms

More and more various chemical media are being applied in enantioseparation; among them, ionic liquids (ILs) have attracted the long-term attention in this decade as green designable solvents. This paper provides comprehensive overview for the applications of ILs in chiral extraction, gas chromatography, liquid chromatography, capillary electrophoresis and other techniques for enantioseparation. Additionally, the important resolution mechanisms based on ILs have also been summarized and discussed. This review focuses on the latest development of enantioseparation methods by using ILs in various modes, leading to meaningful and valuable information to related fields and thus promotes further research and application of reported methods.