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.

Determination of naphthenic acids in produced water by using microchip electrophoresis with integrated contactless conductivity detection.

This study reports for the first time the use of a microchip electrophoresis (ME) device with integrated capacitively coupled contactless conductivity detection (C4D) to analyze naphthenic acids in produced water. A mixture containing 9-anthracenecarboxylic, 1-naphthoic, and benzoic acids was separated and detected using a running buffer composed of 10 mmol L-1 carbonate buffer (pH = 10.2). The separation was achieved within ca. 140 s with baseline resolution greater than 2 and efficiency values ranging from 1.9 × 105 to 2.4 × 105 plates m-1. The developed methodology provided linear correlation with determination coefficients greater than 0.992 for the concentration ranges between 50 and 250 µmol L-1 for benzoic and 9-anthracenecarboxylic acids, and between 50 and 200 µmol L-1 for 1-naphthoic acid. The achieved limit of detection values varied between 4.7 and 7.7 µmol L-1. The proposed methodology revealed satisfactory repeatability with RSD values for a sequence of eight injections between 5.5 and 7.7% for peak areas and lower than 1% for migration times. In addition, inter-day precision was evaluated for sixteen injections (a sequence of four injections performed during four days), and the RSD values were lower than 11.5 and 4.9% for peak areas and migration time, respectively. Five produced water samples were analyzed, and it was possible to detect and quantify 9-anthracenecarboxylic acid. The concentrations ranged from 1.05 to 2.24 mmol L-1 with recovery values between 90.8 and 96.0%. ME-C4D demonstrated satisfactory analytical performance for determining naphthenic acids in produced water for the first time, which is useful for petroleum or oil industry investigation.

Chip-based separation of organic and inorganic anions and multivariate analysis of wines according to grape varieties.

This report describes the use of electrophoresis microchips integrated with contactless conductivity detection for the determination of organic acids and inorganic anions in wine samples and the subsequent classification based on the grape varieties. The best separation was achieved using a buffer composed of 30 mmol L-1 2-(N-morpholino)ethanesulfonic acid, 15 mmol L-1l-histidine and 0.05 mmol L-1 cetyltrimethylammonium bromide (pH 5.8), allowing the determination of chloride, nitrate, sulfate, oxalate, tartrate, maleate, succinate, citrate, acetate, lactate, pyroglutamate and phosphate within ca. 100 s. The relative standard deviations obtained for the migration times were lower than 2%, while the obtained values for peak areas ranged from 2.5 to 8.4%. The limits of detection achieved for all compounds ranged between 3.0 and 12.6 µmol L-1. A total of 18 wines from Brazil and Chile were successfully investigated, including red, white and rosé, and the anionic species were quantified with recovery values between 92 and 117%. A statistical difference has not been observed between the data obtained by using electrophoresis microchips integrated with contactless conductivity detection (ME-C4D) and capillary electrophoresis with ultra-violet detection (CE-UV) and thus the results from newly developed method is validated. Finally, similarities among the anionic profile of wines were investigated by using a multivariate approach, and it was possible to discriminate samples mainly by grapes varieties. Furthermore, the proposed methodology has provided instrumental simplicity and good analytical performance, demonstrating to be useful for routine quality control of wines.

Nonaqueous electrophoresis on microchips: A review.

The use of organic solvents as electrolytic medium in electrophoresis has become an important alternative for the analysis of compounds that exhibit low or no solubility in water. In recent years, nonaqueous electrophoresis has been extensively explored in conventional capillary systems for different applications. On the other hand, this separation strategy is still not as popular as free solution electrophoresis on chip-based platforms due to the effects of solvent in the background electrolyte on the sample injection, detection performance, and microfluidic platform compatibility. In this way, this review summarizes the main achievements on nonaqueous microchip electrophoresis (NAME). To the best of our knowledge, this is the first review dedicated to discuss exclusively nonaqueous electrophoresis on chip-based systems. For this purpose, some important theoretical aspects involved when separations are performed in organic medium, such as equilibrium, interactions and electrophoretic considerations, are included in the review. In addition, the main challenges, advantages and influences of nonaqueous media on the sample injection, detection as well as the choice of the substrate to fabricate chip-based electrophoresis devices are highlighted. Last, examples showing the feasibility of nonaqueous microchip electrophoresis for applications exploiting different methodologies, operational, and instrumental conditions are summarized and discussed. We hope this review can be useful to spread the huge potential of nonaqueous electrophoresis on microfluidic platforms.

Baseline separation of α and ß-acids homologues and isomers in hop (Humulus lupulus L.) by CD-MEKC-UV.

An alternative method for simultaneous baseline separation of α and ß-acids homologues and isomers in hop by CD-MEKC with UV detection was proposed. The optimized background electrolyte was composed of 30 mmol/L sodium tetraborate solution, 45 mmol/L sodium dodecyl sulfate, 20 mmol/L ß-cyclodextrin and 10% v/v acetonitrile. The instrumental conditions were evaluated by using a 33 Box-Benhken experimental design. In order to demonstrate the applicability of the method, 21 hop samples from different varieties were analyzed. The repeatability intra- and interday tests were performed and relative standard deviations lower than 7% for area and migration times were observed. The present method comprehended 8 min analysis time and revealed to be faster and more efficient when compared to previous reports from literature.

Simultaneous determination of aspartame, cyclamate, saccharin and acesulfame-K in powder tabletop sweeteners by FT-Raman spectroscopy associated with the multivariate calibration: PLS, iPLS and siPLS models were compared.

For the first time, a procedure for simultaneous determination of the main artificial sweeteners, aspartame (ASP), cyclamate (CYC), saccharin (SAC), and acesulfame-K (ACSK) by a spectroscopic method associated with the multivariate calibration is proposed. These analytes were quantified in tabletop sweeteners samples using FT-Raman spectroscopy. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used as reference method. Partial least squares (PLS), interval PLS (iPLS), and synergism PLS (siPLS) methods were evaluated in a comparative study where the selected interval models presented better results. Multivariate regression models, such as PLS, iPLS and siPLS were built and the lower root mean square errors for prediction (RMSEP) found were 0.027-0.031% w/w, 0.316-0.363% w/w, 0.082-0.184% w/w, and 0.040-0.049% w/w to ASP, CYC, SAC, and ACSK, respectively. The coefficient of determination for prediction (R2p) varied between 0.978 and 0.979, 0.969-0.977, 0.952-0.994, and 0.959-0.965 for ASP, CYC, SAC and ACSK, respectively. The analysis of model's residues was made by bias and permutation tests to evaluate systematic and trend errors. The selected intervals by iPLS and siPLS were evaluated and the bands related to the vibrational modes of the analytes were assigned with the aid of density functional theory calculations (DFT).