Flavonoid separation by capillary electrophoresis. Effect of temperature and pH

Analysis of natural antioxidants by capillary electromigration methods

In this work, an exhaustive survey of capillary electromigration methods used to analyze natural antioxidants is presented together with some discussion of the use of these substances use as functional foods. This review provides an updated and exhaustive overview of the separation and identification by capillary electrophoresis of natural compounds with antioxidant activity found in natural matrices and/or foods. The compounds concerned are catechins, isoflavones, anthocyanins, phenolic acids, vitamins, as well as other less common natural substances that have shown antioxidant activity.

Capillary electrophoretic separation of phenolic diterpenes from rosemary

The major phenolic diterpenes responsible for the antioxidant properties of rosemary extracts, namely carnosol and carnosic acid, were separated by capillary zone electrophoresis (CZE) using a 56 cm long uncoated fused-silica capillary and a 50 mM disodium tetraborate buffer of pH 10.1. The effect of the buffer type, pH and concentration, and the capillary length on the separation, was studied. Carnosol and carnosic acid were identified in the electrophoregrams of rosemary extracts through their migration times and UV spectra obtained by CZE analysis of pure compounds isolated from a rosemary extract by HPLC fractionation. The CZE method had good reproducibility (relative standard deviation less than 5%) and was applied to compare the contents of carnosol and carnosic acid in solid and oil-dispersed commercial extracts of rosemary and in rosemary leaves. The separation of carnosol and carnosic acid was accomplished in less than 11 min.

Quantification of the production of dihydrokaempferol by flavanone 3-hydroxytransferase using capillary electrophoresis

A sensitive method using capillary electrophoresis for the separation, detection, and quantification of dihydrokaempferol (1) is reported. Well-resolved, sharp symmetrical peaks were obtained in grapefruit leaf extracts for 1, naringenin (2), and the internal standard, naringin (3). Long columns were required to resolve 1 from 2 in crude enzyme reactions and this resulted in run times of 60 min. The limit of detection for 1 was found to be 1.44 ng/microL (4.2 pg). The method showed excellent linearity and reproducibility. The method was used to determine the activity of flavanone 3-hydroxytransferase (F3H) in leaf tissue of grapefruit by quantification of the production of dihydrokaempferol in controlled time course reactions. The sensitivity of the method makes it adaptable to assaying F3H activity in individual young seedlings and/or in small tissue samples and requires only 100 mg of tissue.

Capillary electrophoresis of phytochemical substances

Applications of capillary electrophoresis (CE) for analysis of phytochemical substances (e.g. flavonoids, alkaloids, terpenoids, phenolic acid, quinones and coumarins) are reviewed. For example, CE analysis of sixteen tea ingredients were achieved within 10 min with the good precision (RSDs% <1% for intra-day and 2% for inter-day) and linearity (R(2)>0.990). Quantitation of sanguinarine and chelerythrine, alkaloids from Sanguinaria canadensis L. or Macleaya cordata (Wild) Br. R. by CE showed excellent linearity (R(2)>0.998), precision (RSD%=1.8%) and detection limit (2.4-3.0 microM). Determination of antraquinone-1-sulphonate was also obtained by this technique with good linearity (R(2)>0.9999), precision (RSD%=2%) and detection limit (0.7 microg/ml). Results of CE analysis from several studies are comparable to those of high performance liquid chromatography (HPLC), but the former is more useful for complex mixture samples where the analysis demands higher resolving power. Advantages of CE are high efficiency, low cost, short analysis time and simplicity, whereas disadvantages include low sensitivity comparing to HPLC and limitation of the preparative scale.

Separation of hypericins and hyperforins in extracts of Hypericum perforatum L. using non-aqueous capillary electrophoresis with reversed electro-osmotic flow

The separation of the lipophilic compounds in extracts of Hypericum perforatum L. is demonstrated in a non-aqueous capillary electrophoresis system with reversed electro-osmotic flow. Solvent mixtures of methanol, dimethylsulfoxide and N-methylformamide were used for the electrophoresis media, with addition of ammonium acetate and sodium acetate as electrolytes. The flow was reversed by the addition of the polycation hexadimethrine bromide, and thus negative voltage was applied. The method shows baseline separation between the four hypericins-protopseudohypericin, pseudohypericin, protohypericin and hypericin-whereas total baseline separation between the two hyperforins-hyperforin and adhyperforin-was not achieved. Using a fused-silica capillary (30 cm x 25 microm ID) and a voltage of -25 kV the analysis time of the hypericins and hyperforins was obtainable within 3 min. Application of the method with a fused-silica capillary of a larger internal diameter (48.5 cm x 50 microm ID) and a voltage of -20 kV resulted in analysis times of 8 min, but also lower limits of detection. The maximal attainable voltage was applied in both cases. Simultaneous separation of the flavonoids-although less efficient-may also be achieved. The technique of non-aqueous capillary electrophoresis with reversed electro-osmotic flow provides a very fast technique to evaluate the composition of hypericins and hyperforins in extracts of Hypericum perforatum L.

Analysis of black tea theaflavins by non-aqueous capillary electrophoresis

In this study a new capillary electrophoresis (CE) method was developed to quantify the four major theaflavins occurring in black tea. Where aqueous based CE methods showed poor selectivity and considerable band broadening, non-aqueous CE achieved baseline separation of the theaflavins within 10 min. The effects of the organic solvent composition and background electrolyte concentration on the separation selectivity and electrophoretic mobilities were investigated. Our optimized separation solution consisted of acetonitrile-methanol-acetic acid (71:25:4, v/v) and 90 mM ammonium acetate. This method was used to analyze three black tea samples.

Determination of flavonoids in plant material by HPLC with diode-array and electro-array detections

A high-performance liquid chromatographic (HPLC) method with in-line connected diode-array (DAD) and electro-array (EC) detection to identify and quantify 17 flavonoids in plant-derived foods is described. Catechins were extracted from the samples using ethyl acetate, and quantification of these compounds was performed with the EC detector. Other flavonoids were quantified with DAD after acid hydrolysis. The methods developed were effective for the determination of catechins and other flavonoids in plant-derived foods. Responses of the detection systems were linear within the range evaluated, 20-200 ng/injection (DAD) and 20-100 ng/injection (EC), with correlation coefficients exceeding 0.999. Coefficient of variation was under 10.5%, and recoveries of flavonoids ranged from 70 to 124%. Purity of the flavonoid peaks was confirmed by combining the spectral and voltammetric data.

Analysis of enzymatically glucosylated flavonoids by capillary electrophoresis

HPCE with UV detection was applied to the analyses of enzymatically glucosylated flavonoids, which are used as natural food additives in Japan. Four items, which have flavonol or flavanone as aglycone, were analyzed. Each of these items is a mixture of glycosides with various lengths of maltooligosaccharide chain. On capillary zone electrophoresis with an untreated fused-silica capillary at alkaline pH, glycosides with longer sugar chains migrated more rapidly. Flavonol glycosides with 1-13 glucose units were distinguished with the borate buffer (pH 10.0). Flavanone glycosides needed higher pH values for good separation than flavonol glycosides.

Capillary electrophoresis of natural products

Capillary electrophoresis (CE) and micellar electrokinetic chromatography were used for the separation of widely different compounds from natural materials including antibiotics, humic substances, flavonoids, isoflavonoids, illicit drugs, coumarins, alkaloids, steroids, Chinese herbal preparations, nicotine, caffeine, amphetamines, toxins such as aflatoxins B1, B2, G1, G2, mycotoxins, heptapeptide toxins and others, ephedrine compounds, mineral elements, and natural compounds in biological samples. A discussion of sample extraction and clean-up and the advantages of using CE is also presented.