Analysis of three flavonoids by CE-uV and CE-ESI-MS. Determination of naringenin from a phytomedicine

Determination of Phenolic Compounds by Capillary Zone Electrophoresis-Mass Spectrometry

A CZE-MS method was developed for the determination of several phenolic compounds (phenolic acids, flavonoids). Since the analysis of these components necessitates the application of basic conditions for CZE separation and negative ionization mode for MS detection, the simplest choice was to use 0.5 M NH₄OH and IPA:water (1:1 v/v%) as the background electrolyte and sheath liquid, respectively. The LOD values ranged between 0.004-1.9 mg/L showing that there are relatively large differences in the ionization (and chemical) features of these compounds. The precision data were better than 0.75 RSD% for migration times and were between 5-8 RSD% for peak areas. In order to test the applicability of the developed method, a honey sample was analyzed.

The Research Progress of Chalcone Isomerase (CHI) in Plants

Chalcone isomerase (CHI) is the second rate-limiting and the first reported enzyme involved in the biosynthetic pathway of flavonoids. It catalyzes the intramolecular cyclization reaction, converting the bicyclic chalcone into tricyclic (2S)-flavanone. In this paper, we obtained and analyzed 916 DNA sequences, 1310 mRNA sequences, and 2403 amino acid sequences of CHI registered in NCBI by Jan 2018. The full length of CHI DNA sequences ranges from 218 to 3758 bp, CHI mRNA sequences ranges from 265 to 1436 bp, and CHI amino acid sequences ranges from 35 to 465 amino acid residues. Forty representative species were selected from each family to construct the maximum likelihood tree and analyze the evolutionary relationship. According to the medicinal and agricultural use, 13 specific species were selected, and their physicochemical properties were analyzed. The molecular weight of CHI ranges from 23 to 26 kD, and the isoelectric point of CHI ranges from 4.93 to 5.85. All the half-life periods of CHI are 30 h in mammalian reticulocytes in vitro, 20 h in yeast, and 10 h in E. coli in vivo, theoretically. The consistency of the 13 CHI amino acid sequences is 63.55%. According to the similarity between each sequence, we selected four CHI sequences of Paeonia suffruticosa, Paeonia lactiflora, Taxus wallichiana, and Tradescantia hirsutiflora for secondary structure, three-dimensional protein models, conserved domains, transmembrane structure, and signal peptide prediction analysis. It was found that CHI sequences of Paeonia suffruticosa and Paeonia lactiflora owned a higher similarity; they both share the template 4doi.1.A. The four CHI all have no signal peptides, and they exert their activities in cytoplasm. Then, PubMed, Web of Science, Science Direct, and Research Gate were used as information sources through the search terms 'chalcone isomerase', 'biosynthesis', 'expression', and their combinations to get the latest and comprehensive information of CHI, mainly from the year 2010 to 2018. More than 300 papers were searched and 116 papers were reviewed in the present work. We summarized the classification of CHI, catalytic reaction mechanism of CHI, and progress of genetic engineering regarding CHI clone, expression, and exogenous stimulator regulation. This paper will lay a foundation for further studies of CHI and other functional genes involved in flavonoids biosynthetic pathway.

A Capillary Electrophoresis Electrospray Ionization-Mass Spectrometry Method using a Borate Background Electrolyte for the Fingerprinting Analysis of Flavonoids in Ginkgo biloba Herbal Supplements

A laboratory-built sheath liquid capillary electrophoresis-mass spectrometry interface was used to develop a qualitative method for fingerprinting analysis of 14 structurally similar flavones, flavonols, flavonones, and several representative glycosides in plant samples. The migration order of the flavonoids was dependent on a the number of hydroxyl groups present on the flavonoid B-ring, extent of conjugation, number of glycosidic functionalities, and ability of the flavonoid to form stable borate complexes with the background electrolyte. Parent ion scans of the flavonoids yielded [M-H]-, except for catechol containing flavonoids, which were detected as borate adducts. These adducts can be used diagnostically to determine the presence or absence of catechol groups on unknown polyphenolic compounds. Product ion scans of the flavonoid glycosides and borate adducts typically yielded the deprotonated aglycone fragment as the base peak, which could be used to confirm the base structure of the flavonoid. This method's utility was demonstrated by analyzing flavonoids present in ethanolic extracts of Ginkgo biloba herbal supplements.

Advances of vibrational spectroscopic methods in phytomics and bioanalysis

During the last couple of years great advances in vibrational spectroscopy including near-infrared (NIR), mid-infrared (MIR), attenuated total reflection (ATR) and imaging and also mapping techniques could be achieved. On the other hand spectral treatment features have improved dramatically allowing filtering out relevant information from spectral data much more efficiently and providing new insights into the biochemical composition. These advances offer new possible quality control strategies in phytomics and enable to get deeper insights into biochemical background in terms of medicinal relevant questions. It is the aim of the present article pointing out the technical and methodological advancements in the NIR and MIR field and to demonstrate the individual methods efficiency by discussing distinct selected applications.

Phenolic acids and flavonoids: occurrence and analytical methods

Phenolics are structurally assorted and are generally part of a complex mixture isolated from plant and biological origin matrices. A wide gamut of natural products have been the focus of main study for phenolic compounds while urine and blood are the two main biological fluids that have been analyzed for metabolism studies. Traditional and more advanced techniques have come to prominence for sample preparation, detection, and identification. This review is devoted to a short discussion of the occurrence of phenolic acids and flavonoids, their role in human health, and focuses on a detailed presentation of the analytical methods, concluding with the advantages of analytical methods employed so far and prospects. Strategies and practical aspects for the determination of phenolic acids and flavonoids in biological fluids, beverages, plants, and food are reported. Novel and past applications are provided with significant treatment and detection-related developments on the basis of the employment of separation and non-separation analytical techniques.

Extraction, separation, and detection methods for phenolic acids and flavonoids

The impetus for developing analytical methods for phenolic compounds in natural products has proved to be multifaceted. Hundreds of publications on the analysis of this category of compounds have appeared over the past two decades. Traditional and more advanced techniques have come to prominence for sample preparation, separation, detection, and identification. This review provides an updated and extensive overview of methods and their applications in natural product matrices and samples of biological origin. In addition, it critically appraises recent developments and trends, and provides selected representative bibliographic examples.

Separation mechanism and determination of flavanones with capillary electrophoresis and high-performance liquid chromatography

To probe separation mechanism and determination with capillary zone electrophoresis (CZE) and liquid chromatography (LC), nine compounds with identical flavanone skeleton were studied. Optimum separation of LC was attained with gradient of acetonitrile and 5mM phosphate buffer (pH 6.9). For CE, electrolyte buffer was 4.5mM SDS in 32mM sodium tetraborate buffer (pH 9.2). The distinguishing feature in this work was successful separation of monohydroxyl stereoisomers by CZE. Polarity is generally increased with hydroxyl groups. In a separation mechanism study, polarity would be reduced by intramolecular hydrogen bond between hydroxyl of C5 and carbonyl group of C4. Comparison of the retention results among monohydroxyl flavanones shows polarity with hydroxyl at C6 the least, and that at C4' and C7 nearly equal. Also, elution order of flavones and flavanones would be adverse due to the hydroxyl at C3 in LC. From the numerical value pK(a) of flavanone, the C7-OH is the smallest, and two hydroxyl groups in an adjacent position is always less than the unique one caused by forming a stable 5-membered ring. Investigation of separation mechanism yield only the effect of constituent but also reasonable explanation for contradictory results between Wulf and our laboratory, this due to the hydroxyl at C3.

Antioxidant compounds of propolis determined by capillary electrophoresis-mass spectrometry

Propolis is a resinous hive product rich in antioxidant compounds. Capillary electrophoresis coupled to mass spectrometric detection can provide selective information about the analytes present in complex extracts of propolis and has turned out to be an attractive alternative to HPLC methods. Therefore, a CE-ESI-MS method has been developed for the analysis of antioxidant compounds obtained from propolis. For this purpose, different electrophoretic parameters such as the nature, pH, and concentration of the separation buffer, as well as electrospray parameters (dry gas temperature and flow, nebulising gas pressure, and make-up flow) have been carefully optimised. Different phenolic compounds (e.g. pinobanksin 3-acetate, naringenin, pinocembrin, chrysin, daidzein, quercetin 3',7-dimethyl ether, apigenin, and kaempferid) could be detected. To confirm the identity of the phenolic compounds in propolis extracts, accurate mass data of the molecular ions were obtained by TOF MS. Limits of detection ranging from 6 mg/100 g of raw propolis for chrysin to 58 mg/ 100 g of raw propolis for luteolin, were obtained.

Analysis of flavonoids by CE using capacitively coupled contactless conductivity detection

A CE method employing capacitively coupled contactless conductivity (C(4)D) compared to indirect UV-detection was developed for the analysis of phytochemically relevant flavonoids, such as 6-hydroxyflavone, biochanin A, hesperetin and naringenin. To ensure fast separation at highest selectivity, sensitivity and peak symmetry, the pH value and the concentration of the running BGE had to be optimized regarding both co- and counter-EOF mode. Optimum conditions were found to be 1.0 and 5.0 mM chromate BGE (pH 9.50) in the counter- and co-EOF mode, respectively. Validation of the established CE-C(4)D method pointed out to be approximately seven times more sensitive compared to indirect UV-detection applying the same conditions. The lower LOD defined at an S/N of 3:1 was found between 0.12 and 0.21 microg/mL for the analytes of interest using C(4)D and between 0.77 and 1.20 microg/mL using indirect UV-detection. Compared to an earlier published CE method employing direct UV-detection, C(4)D was found to be approximately two times more sensitive. Due to the lower baseline noise, C(4)D showed an excellent regression coefficient >0.99 compared to 0.93 when using indirect UV detection calibrating within a concentration range between 1 and 10 microg/mL. The influence of the sugar moiety on the conductivity of a flavonoid was studied upon the analysis of the aglycon hesperetin and the rutinosid hesperidin. The sugar moiety in hesperedin shows a higher conductivity compared to hesperetin. Finally, the optimized established CE-C(4)D method was applied to the determination and quantification of naringenin in Sinupret.

Analytical separation and detection methods for flavonoids

Flavonoids receive considerable attention in the literature, specifically because of their biological and physiological importance. This review focuses on separation and detection methods for flavonoids and their application to plants, food, drinks and biological fluids. The topics that will be discussed are sample treatment, column liquid chromatography (LC), but also methods such as gas chromatography (GC), capillary electrophoresis (CE) and thin-layer chromatography (TLC), various detection methods and structural characterization. Because of the increasing interest in structure elucidation of flavonoids, special attention will be devoted to the use of tandem-mass spectrometric (MS/MS) techniques for the characterization of several important sub-classes, and to the potential of combined diode-array UV (DAD UV), tandem-MS and nuclear magnetic resonance (NMR) detection for unambiguous identification. Emphasis will be on recent developments and trends.

Recent trends in the determination of polyphenols by electromigration methods

An overview mapping recent trends in the determination of polyphenols of natural origin (mostly flavonoids) and their synthetic derivatives by electromigration methods is presented. The overview (covering the period of the recent 5 years and comprising 61 references) is focused on capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) with various detection methods. Techniques comprising on-line pre-separation such as isotachophoresis (ITP)-CZE and flow-injection-CZE, chiral separations and CZE evaluation of antioxidation activity are also discussed.

Recent advances in the application of capillary electrophoresis with mass spectrometric detection

This review gives an overview of applications of CE coupled to MS detection published in the literature of the last three years. The works discussed in this paper comprise a wide range of different fields of application. These include important sections such as the analysis of biomolecules, the analysis of pharmaceuticals and their metabolites in different matrices, environmental analysis, and also investigations on the composition of technical products.

Quantitation in capillary electrophoresis-mass spectrometry

CE-MS has evolved into a strong alternative to LC-MS. Most of CE-MS applications deal with characterization and identification. However, quantitative aspects have gained importance in, e.g., pharmaceutical and biotechnological applications. Here we summarize and evaluate various methodological aspects in order to achieve sensitive and reproducible results. Similar to LC-MS, aspects of matrix influence on the electrospray process need to be carefully addressed when quantitative results are intended by CE-MS. Due to a more complicated coupling special emphasis needs to be put on the CE-MS interface. Generally linearity over more than three orders of magnitude can be achieved by CE-ESI-MS. Furthermore, a literature survey has been performed in order to give an overview over quantitative measurements performed by CE-MS. The precision can be doubled when changing from a structural related to an isotopically labeled internal standard. Thus a level of precision better than 5% RSD can be achieved.

Recent applications of capillary electrophoresis-electrospray ionisation-mass spectrometry in drug analysis

A critical review of applications for the period 2000-2004, taken from the Web of Knowledge database, of the technique capillary electrophoresis-electrospray ionisation-mass spectrometry (CE-ESI-MS) in drug analysis is presented. The review is concerned with molecules of mass less than 500 Da, chosen according to selected structural classes in which they give ESI signals primarily as [M+H](+) ions although other ions, such as [M-H](-), [M+Na](+), and [M+NH(4)](+), are also reported. These structural classes are drugs with amine-containing side chains, drugs with N-containing saturated ring structures, 1,4-benzodiazepines, other heterocyclic hypnotics, carbohydrates, sulphonylureas, anthracyclines, sulphonamides, penicillins, cephalosporins, tetracyclines, nitrocatechols, steroids, flavonoids/polyphenols, cannabinols, and miscellaneous molecules. Details are given on the fragmentations, where available, that these ionic species exhibit in-source and in ion-trap, triple quadrupole, and time of flight-mass spectrometers. The review gives a critical evaluation of these recent CE-ESI-MS analytical methods in drug analysis. Analytical information on, for example, sample concentration techniques, CE separation conditions, recoveries from biological media and limits of detection (LODs) are provided. Potential applications of CE-MS to particular drugs or drug classes are also briefly discussed in the text.

Capillary electrophoresis-mass spectrometry in food analysis

This work provides an updated overview (including works published till June 2004) on the principal applications of capillary electrophoresis-mass spectrometry (CE-MS) together with their main advantages and drawbacks in food science. Thus, analysis of amino acids, peptides, proteins, carbohydrates, or polyphenols by CE-MS in different foods is reviewed. Also, other natural compounds (e.g., alkaloids) and toxins analyzed by CE-MS in foods are revised. Moreover, exogenous substances with a potential risk for human health (e.g., pesticides, drugs) detected in foods by CE-MS are included in this work. The usefulness of CE-MS for food analysis and the information that this coupling can provide in terms of processing, composition, authenticity, quality, or safety of foods is also discussed.

Utilization of capillary electrophoresis/mass spectrometry (CE/MSn) for the study of anthocyanin dyes

Hyphenation of capillary electrophoresis with electrospray ionization mass spectrometry was utilized for the monitoring of anthocyanins in wine and wine musts. CE/MS was performed in two electrolytes: 1) an acidic one (chloroacetate-ammonium, pH 2) and 2) a basic one with high selectivity towards derivatives containing vicinal hydroxy groups (borate-ammonium, pH 9). The setup of MS was optimized and the fragmentation of common anthocyanins was studied in detail. Attention was also focused on the fragmentation of anthocyanidin skeleton. The anthocyanidins substituted with hydroxy groups fragment via a cascade of neutral losses of water and carbon monoxide. Fragmentation of anthocyanidins containing a methoxy group on their B-ring starts with the cleavage of methane and/or methyl radical. The optimized method was utilized for the monitoring of changes in anthocyanin profile in red wines as well as the process of release of anthocyanins to wine must.

Analysis of drugs, natural and bioactive compounds containing phenolic groups by capillary electrophoresis coupled to mass spectrometry

This review summarizes the use of capillary electrophoresis (CE) coupled to mass spectrometry (MS) for the analysis of phenolic compounds and its latest developments. Special attention is paid to the different interfaces. The instrumental setups are discussed and demonstrated in a high number of real applications.

Development of capillary zone electrophoresis-electrospray ionization-mass spectrometry for the determination of lamotrigine in human plasma

A method of coupling capillary zone electrophoresis (CZE) with electrospray ionization-mass spectrometry (ESI-MS) detection has been developed for monitoring an antiepileptic drug, lamotrigine (LTG) in human plasma. The CZE-MS was developed in three stages: (i) CZE separation and ESI-MS detection of LTG and tyramine (TRM, internal standard) were simultaneously optimized by studying the influence of CZE background electrolyte (BGE) pH, BGE ionic strength, and nebulizer pressure of the MS sprayer; (ii) sheath liquid parameters, such as pH, ionic strength, organic modifier content, and flow rate of the sheath liquid, were systematically varied under optimum CZE-MS conditions developed in the first stage; (iii) MS sprayer chamber parameters (drying gas temperature and drying gas flow rate) were varied for the best MS detection of LTG. The developed assay was finally applied for the determination of LTG in plasma samples. The linear range of LTG in plasma sample assay was between 0.1-5.0 microg/mL with a limit of detection as low as 0.05 microg/mL and run time less than 6 min. Finally, the concentration-time profile of LTG in human plasma sample was found to correlate well when CZE-ESI-MS was compared to a more established method of high-performance liquid chromatography with ultraviolet detection.