Principles of Electromigration Techniques

Development of a DC-Biased AC-Stimulated Microfluidic Device for the Electrokinetic Separation of Bacterial and Yeast Cells

Electrokinetic (EK) microsystems, which are capable of performing separations without the need for labeling analytes, are a rapidly growing area in microfluidics. The present work demonstrated three distinct binary microbial separations, computationally modeled and experimentally performed, in an insulator-based EK (iEK) system stimulated by DC-biased AC potentials. The separations had an increasing order of difficulty. First, a separation between cells of two distinct domains (Escherichia coli and Saccharomyces cerevisiae) was demonstrated. The second separation was for cells from the same domain but different species (Bacillus subtilis and Bacillus cereus). The last separation included cells from two closely related microbial strains of the same domain and the same species (two distinct S. cerevisiae strains). For each separation, a novel computational model, employing a continuous spatial and temporal function for predicting the particle velocity, was used to predict the retention time (tR,p) of each cell type, which aided the experimentation. All three cases resulted in separation resolution values Rs>1.5, indicating complete separation between the two cell species, with good reproducibility between the experimental repetitions (deviations < 6%) and good agreement (deviations < 18%) between the predicted tR,p and experimental (tR,e) retention time values. This study demonstrated the potential of DC-biased AC iEK systems for performing challenging microbial separations.

Surface sampling capillary electrophoresis-mass spectrometry for a direct chemical characterization of tissue and blood samples

Capillary electrophoresis (CE) is a powerful separation tool for non-targeted analysis of chemically complex samples, such as blood, urine, and tissue. However, traditionally CE requires samples in solution for analysis, which limits information on analyte distribution and heterogeneity in tissue. The recent development of surface sampling CE-mass spectrometry (SS-CE-MS) brings these advantages of CE to solid samples and enables chemical mapping directly from the tissue surface without laborious sample preparation. Here, we describe developments of SS-CE-MS to increase reproducibility and stability for metabolite, lipid, and protein extraction from tissue sections and dried blood spots. Additionally, we report the first electrokinetic sequential sample injection for high throughput analysis. We foresee that the wide molecular coverage from a distinct tissue region in combination with higher throughput will provide novel information on biological function and dysfunction.

Capillary electrophoretic method for the simultaneous determination of nitrate, nitrite and bromate ions in some selected plants

BACKGROUND

Teas and traditional herbs are taken as health remedies in most cultures worldwide. Plants often used in the manufacture of teas and herbal remedies can comprise carcinogenic contaminates, such as nitrates, nitrites and bromate ions. In the present study, a quick method was applied for the simultaneous determination of nitrate (NO₃ ^- ), nitrite (NO₂ ^- ) and bromate (BrO₃ ^- ) ions in some selected plants and tea samples using capillary electrophoresis and a Box-Behnken response surface design for method optimization.

RESULTS

Optimal conditions of 60 mmol L^-1 phosphate buffer solution at pH 3.5, a capillary temperature of 40 °C, applied voltage of -22.5 kV, total capillary length of 61.5 cm (effective length 53.5 cm) with capillary internal diameter of 50 μm, and an injection pressure of 50 mbar for 30 s were selected. The limits of detection for nitrate, bromate and nitrite were 0.49, 1.25 and 0.11 mg L^-1 , whereas linearity values were determined as 0.998, 0.996 and 0.999, respectively.

CONCLUSION

A quick and easy applicable method was developed and the detection of the anions was achievable within 6 min of analysis. From the studied samples (cherry stalk, a dry mixed herbal tea; cherry stalk, dry sticks; dry pomegranate flower; dry olive leaves; and black tea), dry pomegranate flower (13.10 ± 0.62 mg L^-1 ) and cherry stalk, dry mix herbal tea (13.10 ± 0.62 mg L^-1 ) had the highest nitrate content. © 2021 Society of Chemical Industry.

Investigation of selected parameters of capillary zone electrophoresis method for analysis of isolates of outer membrane vesicles

The capillary zone electrophoresis (CZE) has recently been proposed by our group as a novel technique for outer membrane vesicles (OMVs) characterization (J. Chromatography 1621 (2020) 461047). In present work the impact of selected parameters of CZE method on OMVs isolates analysis was assessed. It was shown that the extension of sample injection plug length significantly improves the detectability of macromolecular aggregates in CZE. Moreover, a negligible adsorption of OMVs to both uncoated and polymer-modified (poly(DMA-GMA-MAPS)) capillary walls was proven. Finally, the relaxation effect as well as deformation/polarization of vesicles were demonstrated to affect OMVs electrophoretic mobility. The significance of these findings was discussed.

Evaluation of ion mobility in capillary electrophoresis coupled to mass spectrometry for the identification in metabolomics

Currently, feature annotation remains one of the main challenges in untargeted metabolomics. In this context, the information provided by high-resolution mass spectrometry (HRMS) in addition to accurate mass can improve the quality of metabolite annotation, and MS/MS fragmentation patterns are widely used. Accurate mass and a separation index, such as retention time or effective mobility (μ_eff ), in chromatographic and electrophoretic approaches, respectively, must be used for unequivocal metabolite identification. The possibility of measuring collision cross-section (CCS) values by using ion mobility (IM) is becoming increasingly popular in metabolomic studies thanks to the new generation of IM mass spectrometers. Based on their similar separation mechanisms involving electric field and the size of the compounds, the complementarity of ^DT CCS_N2 and μ_eff needs to be evaluated. In this study, a comparison of ^DT CCS_N2 and μ_eff was achieved in the context of feature identification ability in untargeted metabolomics by capillary zone electrophoresis (CZE) coupled with HRMS. This study confirms the high correlation of ^DT CCS_N2 with the mass of the studied metabolites as well as the orthogonality between accurate mass and μ_eff , making this combination particularly interesting for the identification of several endogenous metabolites. The use of IM-MS remains of great interest for facilitating the annotation of neutral metabolites present in the electroosmotic flow (EOF) that are poorly or not separated by CZE.