Online preconcentration and determination of five alkaloids in Yangxinshi tablet by large-volume sample stacking and micelle to solvent stacking in cyclodextrin-modified electrokinetic chromatography.

The two-step preconcentration technique consisting of large-volume sample stacking (LVSS) and micelle to solvent stacking (MSS) in cyclodextrin-modified electrokinetic chromatography (CDEKC) was developed for the analysis of five cationic alkaloids in complex Chinese herbal prescriptions. Relevant parameters affecting separation and stacking performance were optimized separately. Under the optimal LVSS-MSS-CDEKC conditions, less analysis time and organic solvent were required, and the enhancement factors of analytes ranged from 12 to 15 compared with the normal CDEKC separation mode. Further, all validation results demonstrated good applicability and multiple alkaloids (epiberberine, dehydrocorydaline, jatrorrhizine, coptisine and berberine) in Yangxinshi tablet (YXST) have been simultaneously determined. This approach presents powerful potential for the determination of multiple components in complex preparations of Chinese medicine.

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.

Rapid indirect separation of glutamine enantiomers by micellar electrokinetic chromatography. Analysis of dietary supplements.

Glutamine is the most abundant free proteinogenic α-amino acid. It is naturally produced in the organism and acts as a precursor for the synthesis of different biologically important molecules (such as proteins or nucleotides). However, under stressful conditions, the organism is unable to produce it in enough amounts to function properly. Thus, glutamine (Gln)-based supplements have become increasingly popular over the last decade. Since legal regulations establish that amino acid-based dietary supplements must contain only the L-enantiomer and not the racemate, adequate chiral methodologies are required to achieve their quality control. In this work, an analytical methodology based on the use of micellar electrokinetic chromatography is proposed for the rapid enantiomeric determination of DL-Gln in dietary supplements. Using (+)-1-(9-fluorenyl)-ethyl chloroformate as a derivatizing agent and ammonium perfluorooctanoate as separation medium, the Gln diastereoisomers formed under optimal conditions were separated in 8 min with a resolution of 2.8. The analytical characteristics of the method were evaluated in terms of linearity, precision, accuracy, and limits of detection/quantitation, and they were found appropriate for the analysis of L-Gln-based dietary supplements.

In-capillary screening and quantifying the antioxidants of Yangxinshi Tablet using field-enhanced sample injection-micellar electrokinetic chromatography.

An in-capillary 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate) as oxyradicals combining field-enhanced sample injection with micellar electrokinetic chromatography was developed for screening and determination of the major antioxidants in Yangxinshi Tablet. To obtain simultaneous separation and detection of radicals and analytes, relevant factors were optimized separately. Under the optimum conditions, four compounds including salvianolic acid B, hyperoside, puerarin, and caffeic acid were identified as the major antioxidants. All validation results covering recovery, precision, and stability demonstrated good applicability of the method. On this basis, the total antioxidant activity was successfully evaluated in terms of the decreased peak area of radicals. There was a correlation coefficient of 0.8974 between the total contents of major antioxidants and the total antioxidative activity of the sample. Therefore, these four compounds were selected as combinatorial markers for the quality evaluation of Yangxinshi Tablet. It was concluded that the established method presented a powerful potential to screen and quantify active ingredients in the complex preparation of Chinese medicine.

Nanoemulsion supported microemulsion electrokinetic chromatography coupled with selected preconcentration techniques as an approach for analysis of highly hydrophobic compounds.

In this paper, an oil-in-water (O/W) nanoemulsion (NE) prepared by water cold dilution of an O/W microemulsion (ME) was introduced as a sample matrix in microemulsion electrokinetic capillary chromatography (MEEKC) for the highly hydrophobic compounds analysis. Several model compounds with log PO/W values in the 4.1-10.9 range, from different chemical groups, including retinol, α-tocopherol, cholecalciferol, phylloquinone, menaquinone-7, dichlorodiphenyltrichloroethane, ivermectin have been tested. As a proof of the concept of NE formation, a dynamic light scattering technique was employed to determine the size distribution profile of NE particles. Moreover, due to relatively low conductivity of the NE matrix (50-100 times lower in comparison to the separation buffer) and a negative electric charge provided to hydrophobic compounds through NE dispersed phase, NE matrices have been combined with preconcentration techniques based on electrokinetic dosing, namely field amplified sample injection (FASI) and pressure assisted electrokinetic injection (PAEKI). The detection limits for vitamin K1 and K2-MK7 in the NE matrix in combination with FASI (NE-MEEKC-FASI) as well as PAEKI (NE-MEEKC-PAEKI) were up to 42.9 and 12.1 ng mL-1, respectively. In comparison to standard hydrodynamic injection for microemulsion sample matrix NE-MEEKC-PAEKI grant 45-fold improvement in signal sensitivity. The study presents an innovative approach, as it enables the use of preconcentration techniques for highly hydrophobic compounds (log PO/W > 4), which was not previously possible for implementation in the electromigration techniques. Likewise, the use of organic solvents has been reduced by using ME as a solvent for stock solutions and diluting with water prior to the analysis. The application to real samples was investigated using a dietary supplement containing vitamin K2-MK7 obtained from the fermentation product of soybeans.

Capillary Electrophoresis Mass Spectrometry: Developments and Applications for Enantioselective Analysis from 2011-2020.

It is now more than 25 years since the first report of enantioselective analysis by capillary electrophoresis-mass spectrometry (CE-MS) appeared. This article reviews the power of chiral CE-MS in resolving issues on the use of chiral selector incompatibility with MS and poor detectability encountered for chiral compounds by UV detection. The review begins with the general principles, requirements, and critical aspects of chiral CE-MS instrumentation. Next, the review provides a survey of MS-compatible chiral selectors (CSs) reported during the past decade, and the key achievements encountered in the time period using these CSs. Within the context of the strategies used to combine CE and MS, special attention is paid to the approaches that feature partial filling technique, counter-migration techniques, and direct use of CS, such as molecular micelles. In particular, the development and application of moving and fixed CS for EKC-MS, MEKC-MS, and CEC-MS demonstrate how various chiral compounds analyses were solved in a simple and elegant way during the 2010-2020 review period. The most noteworthy applications in the determination of chiral compounds are critically examined. The operating analytical conditions are detailed in the Tables, and the authors provide commentary on future trends of chiral separations by CE-MS.

The two-phase amphiphilic preconcentration based on surfactants to enrich phenolic compounds from diluted plant extracts and rat urine by micellar electrokinetic chromatography.

A novel technology by two-phase amphiphilic preconcentration based on surfactants was established for enriching phenolic compounds by micellar electrokinetic chromatography (MEKC). The cationic surfactant cetyltrimethylammonium chloride (CTAC) was combined with the anionic analytes that existed in the sample solution before injection. The boundary was formed between CTAC and sodium dodecyl sulfate (SDS) in the background solution when the sample solution was injected into the capillary, where the analytes bound inside micelles were released due to the stronger electrostatic force between SDS and CTAC. This procedure accelerated the separation of analytes from CTAC and greatly improved the enrichment efficiency. The optimal conditions were obtained after a series of optimizations, and the sensitivity enrichment factors of the four analytes were in the range of 39-93 compared to typical injections in capillary zone electrophoresis. Good linearity for matrix-matched calibrations was established for all analytes with R2 values of 0.9993-0.9997. The limits of detection (S/N = 3) for kaempferol, quercetin, salvianolic acid C, and salvianolic acid B were 0.0166, 0.0292, 0.0215, and 0.0195 µg/ml, respectively. The intracapillary RSDs of the analytes ranged from 0.8% to 1.3% for migration time and from 0.4% to 1.8% for peak areas. The developed method was successfully applied to the determination of phenolic compounds, the main compounds of Salvia miltiorrhiza Bge., and had been validated for the determination of spiked recoveries in rat urine.

Chiral Analysis of Non-Protein Amino Acids by Capillary Electrophoresis.

A high number of non-protein amino acids are chiral compounds that have demonstrated to be relevant in different fields. Their determination enables to obtain valuable information related to food quality and safety and has also a high interest from a biological point of view since many of them are key compounds in metabolic pathways or are related with different pathologies.In the development of analytical methodologies to perform chiral separations, capillary electrophoresis (CE) is well-established and one of the most powerful separation techniques as a consequence of its high efficiency, short analysis time, and versatility.This chapter shows, by means of three interesting examples, the application of different CE methodologies to the chiral analysis of non-protein amino acids. The first example describes different electrokinetic chromatography (EKC)-UV methodologies based on the use of negatively charged cyclodextrins as chiral selectors to carry out the stereoselective separation of ten different non-protein amino acids of relevance from a biological or food analysis point of view. The second method illustrates the EKC-UV analysis of L-citrulline and its enantiomeric impurity in food supplements using sulfated-γ-cyclodextrin as chiral selector. The last example shows the simultaneous enantiomeric separation of 3,4-dihydroxy-DL-phenylalanine and all the other chiral constituents involved in the phenylalanine-tyrosine metabolic pathway by using an EKC-MS methodology.

Comparison of GC-MS and MEKC methods for caffeine determination in preworkout supplements.

In this study, GC-MS- and MEKC-based methods for determination of caffeine (CAF) in preworkout supplements were developed and validated. The proposed protocols utilized minimal sample preparation (simple dilution and syringe filtration). The developed methods achieved satisfactory validation parameters, i.e. good linearity (R2 > 0.9988 and R2 > 0.9985 for GC-MS- and MEKC-based method, respectively), satisfactory intra- and interaccuracy (within 92.6-100.7% for method utilizing GC-MS and 92.1-110.3% for protocol based on MEKC) and precision (CV < 15.9% and CV < 6.3% for GC-MS- and MEKC-based method, respectively) and recovery (within 100.1-100.8% for method utilizing GC-MS and 101.5-106.2% for protocol based on MEKC). The LOD was 0.03 and 3 µg/mL for method utilizing GC-MS and MEKC, respectively. The CAF concentrations determined by GC-MS- and MEKC-based methods were found to be in the range of 8.53-11.23 and 8.20-11.61 µg/mL, respectively. Taking into consideration information on the labels, the investigated supplements were found to contain from 110.0 to 167.3% of the declared CAF content, which confirmed the literature reports on incompatibility of the declared product compositions with real ones. Nevertheless, the consumption of examined supplements as recommended by producers did not lead to exceeding the CAF safe limit of 400 mg per day. Additionally, the MEKC-based method allowed for detection and identification of vitamin B3 and B6 in all of the investigated supplement samples, which demonstrated that MEKC-based protocols may be an appropriate assays for simultaneous determination of CAF and vitamins.

The in-capillary- 2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)-sweeping micellar electrokinetic chromatography - Diode array detector method for screening and quantifying trace natural antioxidants from Schisandra chinensis.

An in-capillary 2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)-sweeping micellar electrokinetic chromatography-diode array detector (ABTS+-sweeping MEKC-DAD) method was developed and successfully applied to screening and quantifying antioxidative ingredients from natural products. The parameters affecting sweeping and separation were optimized including components of background electrolyte and sample matrix. Comparing with previously reported MEKC, the sensitivity enhancement factors of trace natural antioxidants obtained by this proposed method were from 17 to 167. The limit of detection was as low as 6 ng·mL-1. The results of other validation parameters including linearity, reproducibility, accuracy and recovery were satisfactory. Seven compounds including schizandrin, schisandrol B, schisantherin B, schisantherin A, schisanhenol, deoxyschizandrin, schisandrin B were identified as the main antioxidants in Schisandra chinensis. It was demonstrated that this developed in-capillary ABTS+-sweeping MEKC-DAD is simple, sensitive, reliable and rapid method for screening and quantifying trace antioxidants from natural products.

Separation and simultaneous determination of seven bioactive components in Tripterygium wilfordii Hook. F. and Tripterygium preparations by micellar electrokinetic capillary chromatography.

A simple, comprehensive, and highly selective MEKC method has been developed for simultaneous analysis of seven bioactive components (triptolide, wilfortrine, wilfordine, wilforgine, wilforine, triptophenolide, and triptonide) in the root extracts of Tripterygium wilfordii Hook. F. (TWHF) and Tripterygium preparations (TPs). Optimal BGE consisted of 10 mM sodium tetraborate, 30 mM SDS, and 30% v/v methanol. The separation voltage was 20 kV and the temperature was 25°C. A DAD was used and the detection wavelength was at 218 nm. Under the optimum conditions, the baseline separation of seven components was achieved in less than 26 min. Excellent precision, good stability, and accuracy were obtained. For all analytes, linear calibrations were established within 10-100 µg/mL. The LOD and LOQ were within 1.2-4.2 µg/mL and 4.0-14 µg/mL, respectively. The developed method was suitable for the determination of key components in TWHF and TPs.

Purification of the total steroidal saponins from fenugreek seeds ( Trigonella foenum- graecum L.) using aqueous two-phase system and determination of diosgenin content using micellar electrokinetic chromatography method.

The total steroidal saponins, particularly its major steroidal sapogenin (diosgenin), are the main active principles of fenugreek seed extract. In this study, an ethanol-salt aqueous two-phase system (ATPS) was explored for the purification of the total steroidal saponins, and the process conditions were optimized by response surface methodology (RSM). Under the optimized conditions, the RSM predicted recovery of the total steroidal saponins in the top phase of ATPS was 97.9%, which agreed with the average experimental recovery (98.3 ± 4.2% ( n = 6)). Moreover, a rapid micellar electrokinetic chromatography (MEKC) method was developed for the determination of diosgenin from extracts. The diosgenin content in the ATPS top phase extract was 3-fold higher than that in crude extract, suggesting this ATPS having a great potential for purification pharmacological active ingredients from fenugreek seeds.

Combining excitation-emission matrix fluorescence spectroscopy, parallel factor analysis, cyclodextrin-modified micellar electrokinetic chromatography and partial least squares class-modelling for green tea characterization.

In this study, an alternative analytical approach for analyzing and characterizing green tea (GT) samples is proposed, based on the combination of excitation-emission matrix (EEM) fluorescence spectroscopy and multivariate chemometric techniques. The three-dimensional spectra of 63 GT samples were recorded using a Perkin-Elmer LS55 luminescence spectrometer; emission spectra were recorded between 295 and 800 nm at excitation wavelength ranging from 200 to 290 nm, with excitation and emission slits both set at 10 nm. The excitation and emission profiles of two factors were obtained using Parallel Factor Analysis (PARAFAC) as a 3-way decomposition method. In this way, for the first time, the spectra of two main fluorophores in green teas have been found. Moreover, a cyclodextrin-modified micellar electrokinetic chromatography method was employed to quantify the most represented catechins and methylxanthines in a subset of 24 GT samples in order to obtain complementary information on the geographical origin of tea. The discrimination ability between the two types of tea has been shown by a Partial Least Squares Class-Modelling performed on the electrokinetic chromatography data, being the sensitivity and specificity of the class model built for the Japanese GT samples 98.70% and 98.68%, respectively. This comprehensive work demonstrates the capability of the combination of EEM fluorescence spectroscopy and PARAFAC model for characterizing, differentiating and analyzing GT samples.

Sensitive analysis of curcuminoids via micellar electrokinetic chromatography with laser-induced native fluorescence detection and mixed micelles-induced fluorescence synergism.

Curcuminoids, the major bioactive constituents of traditional medicine known as turmeric, have exhibited extensive therapeutic benefits. Excited by violet-blue light, curcuminoids can emit native fluorescence, making them possible to be detected with high sensitivity and specificity by laser-induced native fluorescence (LINF). Here, a commercial 445 nm laser diode was used as an excitation source to construct a confocal laser-induced fluorescence (LIF) detector and then a complete capillary electrophoresis (CE) system coupled with LIF detection was established. With three major curcuminoids, curcumin, demethoxy curcumin (DMC) and bisdemethoxy curcumin (BDMC) as target analytes, a micellar electrokinetic chromatography (MEKC) method was proposed using mixed micelles consisting of Triton X-100 and SDS to sensitize the native fluorescence of curcuminoids and enhance their separation efficiency. Fluorescence spectra revealed that the mixed micelles induced fluorescence synergism could enhance the signals of three curcuminoids by 77-, 57-, and 47-fold for curcumin, DMC, and BDMC. After systematic investigation, the optimal separation buffer for curcuminoids was chosen as follows: 20 mM Triton X-100, 20 mM SDS, 30% (v/v) methanol in 10 mM borax solution at pH 10.0. Under these conditions, a baseline separation of three curcuminoids was achieved within 10 min and the detection limits were found to be 4.1, 2.6, and 0.4 ng/mL for curcumin, DMC, and BDMC, respectively. Furthermore, the developed MEKC-LINF method was validated in terms of precision, linearity, accuracy and successfully applied for the determination of three curcuminoids in turmeric, medicinal turmeric liniment, curry seasoning, and human urine samples.

Simultaneous separation and determination of praeruptorin A, B and C by micellar electrokinetic chromatography using sodium dodecyl sulphate and sodium cholate as mixed micelles.

INTRODUCTION: Praeruptorin A, B and C are major bioactive constituents in Peucedani Radix. They display anti-inflammatory effect, anti-hypertension effect, antiplatelet aggregation, potential anti-cancer activities and so on. They are worthy of investigation as potentially novel and versatile drugs. OBJECTIVE: To develop a method using micellar electrokinetic chromatography (MEKC) for the application in simultaneously separation and determination of praeruptorin A, B and C from Peucedani Radix and its medicinal preparations. METHODS: Method optimisation was carried out by investigating influences of significant factors on the separation. The method was subjected to validation. The determination of praeruptorin A, B and C in Peucedani Radix and its drug formulations was accomplished by the developed method. RESULTS: The optimal separation condition was 20 mM borate buffer containing 40 mM sodium cholate (SC), 22 mM sodium dodecyl sulphate (SDS) and 25% (v/v) acetonitrile (pH 10.00); 15 kV of voltage; 25°C of temperature; detection at 224 nm. Under this condition, three analytes were baseline separated within 16 min. A good linearity was obtained with correlation coefficients from 0.9988 to 0.9995. The limits of detection (LODs) and limits of quantitation (LOQs) ranged from 0.50 to 0.80 µg/mL and from 1.50 to 2.50 µg/mL, respectively. The recoveries ranged between 95.3% and 103.4%. CONCLUSION: The proposed method has been successfully applied to the simultaneous determination of praeruptorin A, B and C in Peucedani Radix and its pharmaceutical preparations. Additionally, it could be a potential alternative to the quality control of Peucedani Radix.

Chemometric Assessment of Chromatographic Methods for Herbal Medicines Authentication and Fingerprinting.

Nowadays, increasingly more individuals turn to supplementation of the diet with herbal medicines and many such products are marketed lately. Thus the problem that this article focuses on is that these products are not subjected to rigorous quality control like synthetic drugs are, which rises a constant debate whether the supplements actually contain the herb or mixture of herbs that the manufacturer claims they do. As a solution, micellar electrokinetic chromatography and high performance liquid chromatography were investigated in order to fingerprint and authenticate herbal medicines. For this purpose, minimal sample pre-treatment was applied to several fruit based herbal medicines, which were compared with the ethanolic extract of the respective fruit. The holistic evaluation of the electropherograms and chromatograms was made by using appropriate chemometric tools, such as principal component analysis (PCA), cluster analysis and a combination of PCA and linear discriminant analysis (PCA-LDA). The results suggest that the developed method was able to successfully discriminate between different herbal medicines, based on their raw material content. Moreover, this simple and efficient methodology might also be used for routine screening and authenticity control of different products and could be implemented in any quality control laboratory.

Micro-matrix solid-phase dispersion coupled with MEEKC for quantitative analysis of lignans in Schisandrae Chinensis Fructus using molecular sieve TS-1 as a sorbent.

A simple and effective method was developed for determining lignans in Schisandrae Chinensis Fructus by using a micro-matrix solid phase dispersion (MSPD) technique coupled with microemulsion electrokinetic chromatography (MEEKC). Molecular sieve, TS-1, was applied as a solid supporting material in micro MSPD extraction for the first time. Parameters that affect extraction efficiency, such as type of dispersant, mass ratio of the sample to the dispersant, grinding time, elution solvent and volume were optimized. The optimal extraction conditions involve dispersing 25mg of powdered Schisandrae samples with 50mg of TS-1 by a mortar and pestle. A grinding time of 150s was adopted. The blend was then transferred to a solid-phase extraction cartridge and the target analytes were eluted with 500µL of methanol. Moreover, several parameters affecting MEEKC separation were studied, including the type of oil, SDS concentration, type and concentration of cosurfactant, and concentration of organic modifier. A satisfactory linearity (R>0.9998) was obtained, and the calculated limits of quantitation were less than 2.77µg/mL. Finally, the micro MSPD-MEEKC method was successfully applied to the analysis of lignans in complex Schisandrae fructus samples.

Development of a novel dual CD-MEKC system for the systematic flavonoid fingerprinting of Ligaria cuneifolia (R. et P.) Tiegh.-Loranthaceae-extracts.

The present work deals with the development and validation of a novel dual CD-MEKC system for the systematic flavonoid fingerprinting of Ligaria cuneifolia (R. et P.) Tiegh.-Loranthaceae-extracts. The BGE consisted of 20 mM pH 8.3 borate buffer, 50 mM SDS, a dual CD system based on the combination of 5 mM ß-CD and 2% w/v S-ß-CD, and 10% v/v methanol. The proposed method has been successfully applied to the comparative analysis of extracts from aerial parts and different hosts, geographical areas, and extraction procedures in order to establish the flavonoid fingerprint of L. cuneifolia. The method was validated according to international guidelines. LOD and LOQ, intra and interday precision, and linearity were determined for catechin, epicatechin, procyanidin B2, rutin, quercetin-3-O-glucoside, quercetin-3-O-xyloside, quercetin-3-O-rhamnoside, quercetin-3-O-arabinofuranoside, quercetin-3-O-arabinopyranoside, and quercetin. The CD-MEKC methodology emerges as a suitable alternative to the traditional HPLC for quality control, fingerprinting, and standardization of L. cuneifolia extracts from different sources.

Myrosinase Compatible Simultaneous Determination of Glucosinolates and Allyl Isothiocyanate by Capillary Electrophoresis Micellar Electrokinetic Chromatography (CE-MEKC).

INTRODUCTION: The functional food Cruciferous vegetables contain glucosinolates which are decomposed by the myrosinase enzyme upon tissue damage. The isothiocyanates are the most frequent decomposition products. Because of their various bioactivities, these compounds and the myrosinase is of high interest to many scientific fields. OBJECTIVE: Development of a capillary electrophoresis method capable of myrosinase-compatible, simultaneous quantification of glucosinolates and isothiocyanates. METHODS: Capillary electrochromatography parameters were optimised, followed by optimisation of a myrosinase-compatible derivatisation procedure for isothiocyanates. Vegetable extracts (Brussels sprouts, horseradish, radish and watercress) were tested for myrosinase activity, glucosinolate content and isothiocyanate conversion rate. Allyl isothiocyanate was quantified in some food products. RESULTS: The method allows quantification of sinigrin, gluonasturtiin and allyl isothiocyanate after myrosinase compatible derivatisation in-vial by mercaptoacetic acid. The chromatograhpic separation takes 2.5 min (short-end injection) or 15 min (long-end injection). For the tested vegetables, measured myrosinase activity was between 0.960-27.694 and 0.461-26.322 µmol/min/mg protein, glucosinolate content was between 0-2291.8 and 0-248.5 µg/g fresh weight for sinigrin and gluconastrutiin, respectively. The possible specificity of plants to different glucosinolates was also shown. Allyl isothiocyanate release rate was different in different vegetables (73.13 - 102.13%). The method could also be used for quantification of allyl isothiocyanate from food products. CONCLUSIONS: The presented capillary electrophoresis method requires a minimal amount of sample and contains only a few sample preparation steps, and can be used in several applications (glucosinolate determination, myrosinase activity measurement, isothiocyanate release estimation). Copyright © 2016 John Wiley & Sons, Ltd.

Multivariable optimization of the micellar system for the ionic liquid-modified MEKC separation of phenolic acids.

An ionic liquid (IL)-modified micellar electrokinetic chromatography (MEKC) method was proposed for the separation and determination of eight phenolic acids. In order to increase separation efficiency and selectivity, the micelle system consisting of aqueous mixtures of ILs, Tween 20 and borate was optimized using a D-optimal design. A 16-run experimental plan was carried out. The results indicated that the addition of ILs in background electrolyte could significantly alter the electrophoretic behavior and improve the resolution of target analytes. By evaluating the electropherograms obtained, a satisfactory separation condition for all analytes was achieved in 10min with optimized buffer composed of 0.70% (w/w) 1-butyl-3-methylimidazolium tetrafluoroborate, 8.1% (w/w) polyoxyethylene sorbitan monolaurate (Tween 20) and 10mM sodium borate at pH 9.2. Under these conditions, all calibration curves showed good linearity (r(2)>0.9969), and accuracy (recoveries ranging from 94.71 to 106.85%). Finally, the proposed method was successfully applied to determine the phenolic acids in a Chinese medicine compound, compound danshen dripping pills.