Assay of phenolic compounds in red wine by on-line combination of capillary isotachophoresis with capillary zone electrophoresis

Phenolic acids induced growth of 3D ordered gold nanoshell composite array as sensitive SERS nanosensor for antioxidant capacity assay

A novel method based on surface-enhanced Raman scattering (SERS) was developed to estimate the reducing capacity of phenolic acids by using self-assembled three-dimensionally (3D) ordered gold nanoparticles (GNPs) precursor composite (SiO₂/GNPs) arrays as nanoprobes. In the present work, the 3D ordered SiO₂/GNPs arrays immersed in the growth solution containing different phenolic acids, the SiO₂/GNPs were enlarged to varying degrees. Phenolic acids with one or more phenolic hydroxyl groups served as reductants for the growth of GNPs. The enlargement conditions varied with the different reducing capacity of phenolic acids, exhibiting specific morphologies differ from the complete gold nanoshells (GNSs). Consequently, the UV-vis spectra and SERS spectra for the phenolic acid-treated SiO₂/GNPs arrays were gradually changed. The change of the intensities of the SERS spectra correlated well with phenolic acids concentration which indicated that this SiO₂/GNPs array is a suitable SERS nanoprobe for phenolic acids. Results showed that the higher reducing capacity of phenolic acid, the stronger SERS of the enlarged GNSs. Thus, the SERS results could be used to evaluate the antioxidant capacity of phenolic acids by utilizing 3D ordered SiO₂/GNPs arrays as nanoprobes. The results also indicated that the reducing capacity of these three phenolic acids was in the order gallic acid > syringic acid > vanillic acid. The detection ranges of vanillic acid, syringic acid and gallic acid were 10-250 µM, 10-110 µM and 5-55 µM, respectively.

Analytical characterization of wine and its precursors by capillary electrophoresis

The accurate determination of marker chemical species in grape, musts, and wines presents a unique analytical challenge with high impact on diverse areas of knowledge such as health, plant physiology, and economy. Capillary electromigration techniques have emerged as a powerful tool, allowing the separation and identification of highly polar compounds that cannot be easily separated by traditional HPLC methods, providing complementary information and permitting the simultaneous analysis of analytes with different nature in a single run. The main advantage of CE over traditional methods for wine analysis is that in most cases samples require no treatment other than filtration. The purpose of this article is to present a revision on capillary electromigration methods applied to the analysis of wine and its precursors over the last decade. The current state of the art of the topic is evaluated, with special emphasis on the natural compounds that have allowed wine to be considered as a functional food. The most representative revised compounds are phenolic compounds, amino acids, proteins, elemental species, mycotoxins, and organic acids. Finally, a discussion on future trends of the role of capillary electrophoresis in the field of analytical characterization of wines for routine analysis, wine classification, as well as multidisciplinary aspects of the so-called "from soil to glass" chain is presented.

Determination of polyphenols in Spanish wines by capillary zone electrophoresis. Application to wine characterization by using chemometrics

A capillary zone electrophoresis (CZE) method for the simultaneous determination of 20 polyphenols in wine was developed. The separation was performed using fused-silica capillaries of 75 μm i.d. and a 30 mM sodium tretraborate buffer solution at pH 9.2 with 5% isopropanol as a background electrolyte. A capillary voltage of +25 kV with pressure-assisted (3.5 kPa) separation from minute 18 was applied, thus achieving a total analysis time of <25 min. Instrumental quality parameters such as limits of detection (LOD, values between 0.3 and 2.6 mg/L), linearity (r(2) > 0.990), and run-to-run and day-to-day precisions (RSD values lower than 6.5 and 15.7%, respectively) were established. Three different calibration procedures were evaluated for polyphenol quantitation in wines: external calibration using standards prepared in Milli-Q water, standard addition, and pseudomatrix-matched calibration using wine as a matrix. For a 95% confidence level, no statistical differences were observed, in general, between the three calibration methods (p values between 0.11 and 0.84), whereas for some specific polyphenols, such as cinnamic acid, syringic acid, and gallic acid, results were not comparable when external calibration was used. The CZE method using pseudomatrix-matched calibration was then proposed and applied to the analysis of polyphenols in 49 Spanish wines, showing satisfactory results and a wide compositional variation between wines. Electrophoretic profiles and other compositional data (e.g., peak areas of selected peaks) were considered as fingerprints of wines to be used for characterization and classification purposes. The corresponding data were analyzed by principal component analysis (PCA) to extract information on the most significant features contributing to wine discrimination according to their origins. Results showed that a reasonable distribution of wines depending on the elaboration areas was found, tyrosol and gallic, protocatechuic, p-coumaric, and caffeic acids being some representative discriminant compounds.

Application and potential of capillary electroseparation methods to determine antioxidant phenolic compounds from plant food material

Antioxidants are one of the most common active ingredients of nutritionally functional foods which can play an important role in the prevention of oxidation and cellular damage inhibiting or delaying the oxidative processes. In recent years there has been an increased interest in the application of antioxidants to medical treatment as information is constantly gathered linking the development of human diseases to oxidative stress. Within antioxidants, phenolic molecules are an important category of compounds, commonly present in a wide variety of plant food materials. Their correct determination is pivotal nowadays and involves their extraction from the sample, analytical separation, identification, quantification and interpretation of the data. The aim of this review is to provide an overview about all the necessary steps of any analytical procedure to achieve the determination of phenolic compounds from plant matrices, paying particular attention to the application and potential of capillary electroseparation methods. Since it is quite complicated to establish a classification of plant food material, and to structure the current review, we will group the different matrices as follows: fruits, vegetables, herbs, spices and medicinal plants, beverages, vegetable oils, cereals, legumes and nuts and other matrices (including cocoa beans and bee products). At the end of the overview, we include two sections to explain the usefulness of the data about phenols provided by capillary electrophoresis and the newest trends.

Multivariant optimization, validation, and application of capillary electrophoresis for simultaneous determination of polyphenols and phenolic acids in Brazilian wines

A method for the simultaneous determination of the stilbene resveratrol, four phenolic acids (syringic, coumaric, caffeic, and gallic acids), and five flavonoids (catechin, rutin, kaempferol, myricetin, and quercetin) in wine by CE was developed and validated. The CE electrolyte composition and instrumental conditions were optimized using 2(7-3) factorial design and response surface analysis, showing sodium tetraborate, MeOH, and their interaction as the most influential variables. The optimal electrophoretic conditions, minimizing the chromatographic resolution statistic values, consisted of 17 mmol/L sodium tetraborate with 20% methanol as electrolyte, constant voltage of 25 kV, hydrodynamic injection at 50 mbar for 3 s, and temperature of 25 degrees C. The R(2) values for linearity varied from 0.994 to 0.999; LOD and LOQ were 0.1 to 0.3 mg/L and 0.4 to 0.8 mg/L, respectively. The RSDs for migration time and peak area obtained from ten consecutive injections were less than 2% and recoveries varied from 97 to 102%. The method was applied to 23 samples of inexpensive Brazilian wines, showing wide compositional variation.

Advanced separation methods of food anthocyanins, isoflavones and flavanols

In recent years, increasing knowledge of the positive health effects of food polyphenols has prompted the need to develop new separation techniques for their extraction, fractionation and analysis. This article provides an updated and exhaustive review of the application of counter-current chromatography, high performance liquid chromatography, capillary electrophoresis, and their hyphenation with mass spectrometry to the study of food polyphenols. Flavonoids constitute the largest class of polyphenols, widely spread in the plant kingdom and common in human diet which has been the most widely studied with respect to their antioxidant and biological activities. The main subgroups are anthocyanins, catechins, isoflavones, flavonols and flavones. They are reported to exhibit antioxidant, anti-carcinogenic, anti-inflammatory, anti-atherogenic, anti-thrombotic, and immune modulating functions, among others. Since red fruit anthocyanins, soy isoflavones and flavanols from grapes and teas are currently the most used phenolic compounds for producing new nutraceuticals and functional foods, this review is focused on these three flavonoid groups.

Matrix-less laser desorption/ionisation mass spectrometry of polyphenols in red wine

Matrix-assisted laser desorption/ionisation (MALDI) of small molecules is challenging and in most cases impossible due to interferences from matrix ions precluding analysis of molecules <300-500 Da. A common matrix such as ferulic acid belongs to an important class of compounds associated with antioxidant activity. If the shared phenolic structure is related to the propensity as an active MALDI matrix then it follows that direct laser desorption/ionisation should be possible for polyphenols. Indeed matrix-less laser desorption/ionisation mass spectrometry is achieved whereby the analyte functions as a matrix and was used to monitor low molecular weight compounds in wine samples. Sensitivity ranging from 0.12-87 pmol/spot was achieved for eight phenolic acids (4-coumaric, 4-hydroxybenzoic, caffeic, ferulic, gallic, protocatechuic, syringic, vanillic) and 0.02 pmol/spot for trans-resveratrol. Additionally, 4-coumaric, 4-hydroxybenzoic, caffeic, ferulic, gallic, syringic, vanillic acids and trans-resveratrol were identified in wine samples using accurate mass measurements consistent with reported profiles based on liquid chromatography (LC)/MS. Minimal sample pre-treatment make the technique potentially appropriate for fingerprinting, screening and quality control of wine samples.

Determination of phenolic acids by capillary zone electrophoresis and HPLC

Selected phenolic acids are determined by capillary zone electrophoresis and HPLC, each using UV detection. The optimised CZE background electrolyte contained 50 mM acetic acid, 95 mM 6-aminocaproic acid, 0.1% polyacrylamide, 1% polyvinylpyrrolidone, and 10% methanol. Twelve phenolic acids (gallic, p-hydroxybenzoic, 3,4-dihydroxybenzoic, vanillic, syringic, o-coumaric, p-coumaric, caffeic, sinapic, ferulic, salicylic and chlorogenic) were separated within 10 minutes. Chromatographic separation of these phenolic acids was carried out on an Eclipse XBD C8 column using a mobile phase gradient (acetonitrile / methanol / water / 0.1% phosphoric acid); all were separated within 25 minutes. Electrophoretic and chromatographic determinations of ferulic and chlorogenic acids were compared on barley, malt, and potato samples. The methods’ characteristics were: linearity (1–20 mg ml and 0.2–4 mg ml−1), accuracy (recovery 94 ± 5% and 96 ± 4%), intra-assay repeatability (4.1% and 3.5%), and detection limit (0.2 and 0.02 mg ml−1).

Determination of some phenolic acids in Majorana hortensis by capillary electrophoresis with online electrokinetic preconcentration

An online accumulation/mobilization preconcentration technique based on a dynamic pH junction technique and electrokinetic injection was employed for analysis of phenolic acids (sinapic, ferulic, coumarinic, caffeic, syringic, vanillic, and 4-hydroxybenzoic acid) in extracts from Majorana hortensis leaves. Samples were extracted by pressurized solvent extraction with acetone at 150 degrees C and 15 MPa. The capillary electrophoretic method employed 50 mmol.L (-1) sodium borate, pH 9.5, as the sample electrolyte, 50 mmol.L (-1) sodium phosphate, pH 2.5, as the background electrolyte, and 50 mmol.L (-1) sodium phosphate, pH 2.5, with 60 mmol.L (-1) sodium dodecyl sulfate as the mobilization electrolyte. The method allowed 720-fold to 5560-fold preconcentration of the phenolic acids during 30 min of electrokinetic accumulation with detection limits from 0.38 to 4.22 ng.mL (-1).

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.

CE methods applied to the analysis of micronutrients in foods

This article reviews the applications of CE that are relevant to the analysis of small molecules in foods. CE has been applied to a wide range of important areas of food analysis and is rapidly being established as an alternative technique to chromatographic methods including HPLC and GC within analytical food and research laboratories. In recent years the analysis of food by CE has become more frequent and important and as such a variety of compounds have been separated and quantified. Although many other analytes have been detected by CE, this review will highlight areas relating primarily to the rather broad chemical classes of free amino acids, carbohydrates, organic acids, vitamins and a variety of antioxidants. In addition, information relating to the analyte, sample matrix, mode of CE employed, scope of the methodology and the detection and derivatization of the small molecules are considered and discussed.

Determination of iodide in samples with complex matrices by hyphenation of capillary isotachophoresis and zone electrophoresis

A method has been developed for the determination of iodide in mineral water, seawater, cooking salt, serum, and urine based on hyphenation of capillary ITP and zone electrophoresis. A commercially available instrumentation for capillary ITP with column-switching system was used. ITP served for removal of chloride present in the analyzed samples in a ratio of 10(6)-10(7):1 to iodide, zone electrophoresis was used for evaluation. Isotachophoretic separation proceeded in a capillary made of fluorinated ethylene-propylene copolymer of 0.8 mm id and 90 mm total length to the bifurcation point filled with a leading electrolyte (LE) composed of 8 mM HCl + 16 mM beta-alanine (beta-Ala) + 10% PVP + 2.86 mM N(2)H(4)x2HCl, pH 3.2; and a terminating electrolyte composed of 8 mM H(3)PO(4) + 16 mM beta-Ala + 10% PVP + 5 mM N(2)H(4), pH 3.85 for all the matrices except seawater. For ITP of seawater the LE consisted of 50 mM HCl + 100 mM beta-Ala + 10% PVP + 2.86 mM N(2)H(4)x2HCl, pH 3.52. Distance of conductivity detector from the injection point and bifurcation point was 52 and 38 mm, respectively. Zone electrophoresis was performed in a capillary made of fused silica of 0.3 mm id and 160 mm total length filled with LE from isotachophoretic step. LODs reached for all matrices were 2-3x10(-8) M concentration (2.5-4 microg/L) enabled monitoring of iodide in all analyzed samples with RSD 0.4-9.3%. Estimated concentrations of iodide in individual matrices were 10(-6)-10(-8) M.

Application of CE in hydrodynamically closed systems for analysis of bioactive compounds in food

CE is a family of electrokinetic separation techniques that separate compounds based upon differences in electrophoretic mobilities, phase partitioning, pI, molecular size, or a combination of one or several of these properties. CE has been used in several modes to analyze and characterize a wide variety of analytes from simple inorganic ions, small organic molecules, peptides, proteins, nucleic acids to virus, microbes and particles. Food consists of a complex mixture of a variety of components, many of which are biologically active. Components classified as "nutrients" are essential for growth, maintenance, and repair of the body. Other food constituents, typically occurring in small quantities, are classified as "biologically active substances" and they have beneficial or harmful effects on human health. There are two types of biologically active substances in food - naturally occurring and food additives. The bioactive compounds of food that will be mentioned in this review are inorganic and organic acids, amino acids, vitamins, phenolic compounds, biogenic amines, antinutrients, toxins, etc. This review is focused on the application of CE with hydrodynamically closed system (suppression of EOF) for the analysis of the above-mentioned compounds. CE can be an alternative method to HPLC or other methods for analysis of bioactive compounds in food. The main advantages of CE are low running cost (at least ten times than HPLC) and consideration to environment (hundreds of microliters of diluted water based electrolyte per analysis).

Study of low-molecular weight organic acids in maize roots under the stress of cadmium using capillary zone electrophoresis

An indirect CE method was developed for the study of low-molecular weight organic acids (LMWOAs) in maize under the stress of cadmium. The influences of indirect reagents (phthalate, salicylic acid, and benzoic acid), coion concentration, and pH were studied. A buffer composed of 15 mmol/L benzoate and 0.2 mmol/L CTAB (pH 5.7) was used in the organic acid determination. The detection limit ranged between 0.5 and 6 micromol/L. The RSD (n = 14) of the method was found to be in the range of 0.11-0.49% for migration time and 1.25-4.72% for peak area. In the maize roots, obvious increases of LMWOAs were observed when the plants were under the stress of cadmium and/or organic acids. The recovery of standard organic acids added in real samples ranged from 85 to 116%.

Recent progress in capillary ITP

ITP has been attracting constant attention for many years due to its principal capability to concentrate trace analytes by several orders of magnitude. In the current capillary format, it is able to concentrate trace analytes diluted to several microliters of an original sample into concentrated zones having volumes in the range of picoliters. Due to this reason, ITP holds an important position in many current multistage and multidimensional separation schemes. This article links up previous reviews on the topic and summarizes the progress of analytical capillary ITP since 2002. Almost 100 papers are reviewed that include methodological novelties, instrumental aspects, and analytical applications. Papers using ITP and/or isotachophoretic principles as part of multistage and/or multidimensional separation schemes are also included.

Optimization of CZE for analysis of phytochemical bioactive compounds

Advantages of CZE such as high efficiency, low cost, short analysis time, and easy implementation result in its wide applications for analysis of phytochemical bioactive compounds (e.g. flavonoids, alkaloids, terpenoids, phenolic acid, saponins, anthraquinones and coumarins). However, several aspects, including sample preparation, separation, and detection have significant effects on CZE analysis. Therefore, optimization of these procedures is necessary for development of the method. In this review, sample preparation such as extraction method and preconcentration, separation factors including buffer type, concentration and pH, additives, voltage and temperature, as well as detection, e.g. direct and indirect UV detection, LIF and MS were discussed for optimization of CZE analysis on phytochemical bioactive compounds. The optimized strategies were also reviewed.

Integrated isotachophoretic preconcentration with zone electrophoresis separation on a quartz microchip for UV detection of flavonoids

A quartz microchip integrated isotachophoretic (ITP) preconcentration with zone electrophoresis (ZE) separation was fabricated using a novel multi-point pressure method featured in normal temperature and lower pressure during bonding process. ITP followed by subsequential ZE of two flavonoids, quercetin and isorhamnetin on the microchip was performed consecutively on the homemade microfluidic workstation with UV detection, resulting in a decreased detectable concentration of 32-fold, compared to the ZE mode only, and their detection limits decreased down to 0.2 microg/mL and 1.2 microg/mL, respectively.

Analysis of selected constituents in methanolic extracts ofHypericum perforatum collected in different localities by capillary ITP-CZE

The on-line combination of CZE with capillary ITP (ITP-CZE) was used for the separation and quantification of selected flavonoids and phenolic acids in Hypericum perforatum leaves and flowers collected in six different localities in Slovakia. The leading electrolyte in the ITP preseparation step was 10 mM HCl with Tris as counterion (pH* 7.2). The terminating electrolyte was 50 mM boric acid of pH* 8.2 (adjusted with barium hydroxide). The BGE in the electrophoretic step contained 25 mM beta-hydroxy-4-morpholinopropanesulfonic acid (MOPSO), 50 mM Tris, 65 mM boric acid, pH* 8.3. The content of methanol in all electrolytes was 20% v/v. The total time of the analysis (including the preseparation step) was approximately 35 min. The rectilinear calibration ranges were between 0.125 and 5.0 microg/mL with kaempferol as internal standard. The correlation coefficients ranged between 0.9912 (for quercitrin and chlorogenic acid) and 0.9988 (for isoquercitrin). The RSD values are between 0.86 and 7.78% (n = 6) when determining rutin and quercetin (4 microg/mL). The optimized method was employed for the assay of flavonoids in medicinal plant extract of different collections of Hypericum perforatum haulm. The variability of the content of the active components depending on the place of collection was confirmed.

Capillary isotachophoresis from the student point of view – images and the reality

A review of some fundamental aspects of ITP from the student point of view, imaginations of some basic facts and laws, use of ITP, and the recent trends are presented. The results of theoretical computations of ITP separation processes are added for comparison of imaginations with the exact mathematical description.

Analysis of phenolic acids as chloroformate derivatives using solid phase microextraction–gas chromatography

In the presented study, a simple and original procedure of phenolic acids derivatization treated by ethyl and methyl chloroformate performed in an aqueous media consisting of acetonitrile, water, methanol/ethanol and pyridine has been modified and optimized. Seven phenolic acid standards-caffeic, ferulic, gallic, p-coumaric, protocatechuic, syringic and vanillic were derivatized into corresponding methyl/ethyl esters and subsequently determined by the means of gas chromatography connected to the flame-ionisation detector (FID). Some selected validation parameters as linearity, detection and quantitation limits and peak area repeatability were valued. The total time of gas chromatography (GC) analysis was 24 min for methyl chloroformate and 30 min for ethyl chloroformate derivatization. The more suitable methyl chloroformate derivatization was used for further experiments on the possibility of multiple pre-concentration by the direct solid phase microextraction technique (SPME). For this purpose, polyacrylate (PA), polydimethylsiloxane (PDMS), carboxen/polydimethylsiloxane (CAR/PDMS) and polydimethylsiloxane/divinylbenzene (PDMS/DVB) fibres were tested and the extraction conditions concerning time of extraction, temperature and time of desorption were optimized. The most polar PA fibre gave the best results under optimal extraction conditions (50 min extraction time, 25 degrees C extraction temperature and 10 min desorption time). As a result, the total time of SPME-GC analysis was 74 min and an increase in method sensitivity was reached. The limits of quantitation (LOQ) of p-coumaric, ferulic, syringic and vanillic acid esters after SPME pre-concentration were 0.02, 0.17, 0.2 and 0.2 microg mL(-1), respectively, showing approximately 10 times higher sensitivity in comparison with the original GC method.

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 electromigration methods for food analysis

This article reviews the latest developments in the application of capillary electromigration methods for the analysis of foods and food components. Nowadays, methods based on CE techniques are becoming widely used in food analytical and research laboratories. This review covers the application of CE to analyze amino acids, biogenic amines, peptides, proteins, DNAs, carbohydrates, phenols, polyphenols, pigments, toxins, pesticides, vitamins, additives, small organic and inorganic ions, chiral compounds, and other compounds in foods, as well as to investigate food interactions and food processing. The use of microchips as well as other foreseen trends in CE analysis of foods is discussed. Papers that were published during the period June 2002-June 2005 are included following the previous review by Frazier and Papadopoulou (Electrophoresis 2003, 24, 4095-4105).

Determination of organic acids in wine by zone electrophoresis on a chip with conductivity detection

An appropriate combination of separation mechanisms (simultaneous use of differences in pK values, host-guest complexations, and the ionic strength dependences of the actual ionic mobilities) provided zone electrophoresis (ZE) resolution of 22 organic and inorganic acids expected in wines on a polymethylmethacrylate (PMMA) chip with integrated conductivity detection. These separating conditions offered a framework for the ZE determination of organic acids responsible for some important organoleptic characteristics of wines (tartrate, malate, succinate, acetate, citrate, and lactate). The ZE procedure developed in this context is simple and rapid (ca. 10 minutes' analysis time), while affording reproducible migration and quantitation data for the acids. For example, 0.8-2.0% RSD values characterized the migration times of the acids for 25 repeated ZE runs with the same sample carried out in 5 days in the background electrolyte solution prepared freshly on a daily basis, while 3-5% RSD values were typical for the accompanying peak area data. The concentration ranges within which the acids of analytical interest could be determined in one ZE run covered all wine samples included in our study (100-400-fold sample dilutions were needed to work under the conditions corresponding to the validities of the calibration data). 90-110% recoveries of the acids as obtained repeatedly for one of the reference wine samples used in our experiments indicate a good predisposition of the present method to provide accurate analytical results. This statement also supports the results from the determination of the acids in reference wine samples with claimed concentrations of malic (five samples), tartaric (one sample), and lactic (one sample) acids.

Capillary electrophoresis in food authenticity

Food authenticity is a term which simply refers to whether the food purchased by the consumer matches its description. False description can occur in many forms, from the undeclared addition of water or other cheaper materials, or the wrong declaration of the amount of a particular ingredient in the product, to making false statements about the source of ingredients i.e., their geographic, plant, or animal origin. The aim of this review is to summarize applications of capillary electrophoresis in food authentication.