Simultaneous separation of 17 anions by capillary electrophoresis with the addition of an organic solvent

Combination of large-volume sample stacking with polarity switching and micelle electrokinetic chromatography for the analysis of anion compounds in Yangxinshi tablets

INTRODUCTION

Yangxinshi tablet (YXST) is a traditional Chinese medicine preparation characterized by its high efficacy and safety for the treatment of cardiovascular diseases. Anionic compounds have been revealed as potential active components. However, there is currently limited research regarding its quality control.

OBJECTIVE

We aimed to establish a strategy for the simultaneous separation and determination of five key anionic compounds in YXST.

METHOD

A sensitive and efficient analytical method was developed and applied for the simultaneous separation and determination of five key compounds in YXST using large-volume sample stacking with polarity switching and micelle electrokinetic chromatography (LVSS-PS-MEKC) coupled with diode array detection. Crucial parameters, including sample volume, applied voltage, composition and pH of the running buffer, concentration of organic modifier, and switching time of the polarity, were systematically evaluated and optimized using a single variable method to enhance separation performance. Furthermore, the impact of cyclodextrin and sodium dodecyl sulfate as electrolyte modifiers was also investigated.

RESULTS

Under the optimal conditions, baseline separation of the five compounds (daidzein, puerarin, glycyrrhiztinic acid, chlorogenic acid, and salvianolic acid B) was achieved within 20 min. In comparison to the conventional MEKC mode, the constructed LVSS-PS-MEKC method exhibited a more than sixfold increase in the enrichment factor. The method was validated in terms of linearity, precision, accuracy, 24 h stability, and recovery and successfully applied to analyze YXST samples.

CONCLUSION

A sensitive strategy was developed for the simultaneous separation and determination of five key anionic components in YXST, offering a robust and efficient strategy for pharmaceutical analysis.

Capillary electrophoresis separations with deep eutectic solvents as greener separation media: A proof-of-concept study

Capillary electrophoresis (CE) has conventionally been classified into aqueous and non-aqueous categories based on the types of buffer solvents employed. Traditionally, non-aqueous CE has always been associated with the use of organic solvents, which are considered hazardous to health and environmentally detrimental. In this work, we introduce deep eutectic solvents (DESs) as CE separation media for the first time, presenting a novel and environmentally friendly approach to CE separations. The DES employed consists of proline and urea (Proline:Urea, PU), both of which are naturally occurring compounds that are readily available, cost-effective, and environmentally benign. Various fundamental aspects of the DES-type CE media were investigated, including thermal property, viscosity, electroconductivity, Joule heating effect, and compatibility with detectors. A simulated complex mixture of ten naphthalene-based compounds with varied charges and sizes was separated using the DES-based medium in capillary zone electrophoresis (CZE) mode. Moreover, we also established a DES-based micellar electrokinetic chromatography (MEKC) system utilizing Tween-20 as the surfactant. Six structurally similar naphthalene derivatives (isomers) that couldn't be resolved by CZE were effectively separated due to their strong hydrophobic interaction with Tween-20 micelles within the DES medium. Given that DESs are "designer" solvents with highly tunable properties and environmentally friendly characteristics, this study demonstrates the potential of employing DESs as an alternative to organic solvents for greener CE separations.

Determination of 13-cis-Retinoic Acid and Its Metabolites in Plasma by Micellar Electrokinetic Chromatography Using Cyclodextrin-Assisted Sweeping for Sample Preconcentration

The online preconcentration technique, cyclodextrin-assisted sweeping (CD-sweeping), coupled with micellar electrokinetic chromatography (MEKC) was established to determine 13-cis-retinoic acid (13-cis-RA), all-trans-retinoic acid (all-trans-RA) and 4-oxo-13-cis-retinoic acid (4-oxo-13-cis-RA) in human plasma. A CD-sweeping buffer (45 mM borate (pH 9.2), containing 80 mM sodium dodecyl sulfate (SDS) and 22 mM hydroxypropyl β-CD (HP-β-CD) was introduced into the capillary and, then, the sample dissolved in 70 mM borate (pH 9.2): methanol = 9:1 (v/v) was injected into capillary by pressure. The separation voltage was 23 kV. Compared to the conventional cyclodextrin-micellar electrokinetic chromatography (CD-MEKC) method, the new technique achieved 224-257-fold sensitivity enrichment of analytes. The limits of detection of 13-cis-RA, all-trans-RA were 1 ng/mL, whereas that of 4-oxo-13-cis-RA was 25 ng/mL in plasma. The linear ranges of 13-cis-RA, all-trans-RA were between 15 and 1000 ng/mL, whereas that of 4-oxo-13-cis-RA was between 75 and 1500 ng/mL. The coefficient of correlation between the concentration of analytes and peak area ratio of analytes and internal standard (2, 4-dihydroxy-benzophenone) for intra-day (n = 3) and inter-day (n = 5) analyses were both greater than 0.999. The optimized experimental conditions were successfully applied to determine 13-cis-retinoic acid and its metabolites in plasma samples from a patient during the administration of 13-cis-RA for treating acne.