Flavonoids electrochemical detection

Knowledge of the identity of phenolic compounds in food facilitates the analysis and discussion of potential antioxidant effects. Thus studies of phenolic compounds as antioxidants in food should usually by accompanied by the identification and quantification of the phenols. Reversed-phase HPLC combined with UV-VIS or electrochemical detection is the most common method for quantification of individual flavonoids and phenolic acids in foods (Merken and Beecher, 2000 Mattila and Kumpulainen, 2002), whereas HPLC combined with mass spectrometry has been used for identification of phenolic compounds (Justesen et al, 1998). Normal-phase HPLC combined with mass spectrometry has been used to identify monomeric and dimeric proanthocyanidins (Lazarus et al, 1999). Flavonoids are usually quantified as aglycones by HPLC, and samples containing flavonoid glycosides are therefore hydrolysed before analysis (Nuutila et al, 2002). 

SM Lunte. Structural classification of flavonoids in beverages by liquid chromatoaphy with ultraviolet-visible and electrochemical detection. J Chromatogr 384 371-382, 1987. 

Capillary electrophoresis (CE) has also been employed for the analysis of flavonols.17 In fact, CE methods coupled with electrochemical detection (ECD) are increasingly being employed for the analysis of flavonoids because of the minimal sample volume required, short analysis time, and high separation efficiency.17 The limit of detection for quercetin and kaempferol by CE/ECD methods are comparable to those obtained by LC/MS. The primary drawback of using CE is low repeatability of retention times as compared with HPLC. 

Cao Y, Chu Q, Fang Y and Ye J, Analysis of flavonoids in Ginkgo biloba L. and its phytopharmaceuticals by capillary electrophoresis with electrochemical detection. Anal Bioanal Chem 374 294-299 (2002). 

A significant amount of literature regarding the antioxidant properties of flavonoids and other plant polyphenols is available. As the essence of redox chemistry involves electron transfer, it seems natural that electrochemical detection rivals spectrophotometric detection techniques for the compounds that are supposed to be antioxidants. With the improvements in electrochemical detector geometries and electronics over the last decade, coupled with a requirement for increased sensitivity, the use of electrochemical detectors offers significant additional advantages when combined with the traditional UV-VIS detection in the analysis of flavonoids and other plant polyphenols. ... 

Milhury, P.E. Analysis of complex mixtures of flavonoids and polyphenols hy high-performance hquid chromatography electrochemical detection methods. Methods Enzy-mol. 2001, 335, 15-26. 

Electrochemical detection is very sensitive for the compounds that can be oxidized or reduced at low-voltage potentials. Therefore, it could also be applied in the HPLC analysis of phenolic acids that are present in natural samples at very low concentrations. With the recent advances in electrochemical detection, multi-electrode array detection is becoming a powerful tool for detecting phenolic acids and flavonoids in a wide range of samples. The multi-channel coulometric detection system may serve as a highly sensitive way for the overall characterization of antioxidants the coulometric efficiency of each element of the array allows a complete voltametiic resolution of analytes as a function of their reaction (redox) potential. Some peaks may be resolved by the detector, even if they are unresolved when they leave the HPLC column. ... 

The advantage of LC-MS detection over UV or electrochemical detection is its tremendously improved selectivity. Flavonoids, phenolic acids but also certain oxidation and degradation products of procyanidins can be suppressed by monitoring specific ion traces. Sample clean up procedures can therefore be minimized. Fig. (10) illustrates the benefit of LC-MS detection in the analysis of complex matrices. A major drawback of this technology in the analysis of procyanidins is its low sensitivity, even compared to UV detection [282],... 

Huck, C.W. Bonn, G.K. Evaluation of detection methods for the reversed-phase HPLC determination of 3, 4, 5 -tri-methoxyflavone in different phytopharmaceutical products and in human serum. Phytochem. Anal. 2001,12,104—109. Huck, C.W. Huber, C.G. Ongania, K.H. Bonn, G.K. Isolation and characterization of methoxylated flavones in the flowers of Primula veris hy Uquid chromatography and mass spectrometry. J. Chromatogr. A, 2000, 870,453-462. Milhury, P.E. Analysis of complex mixtures of flavonoids and polyphenols hy high-performance hquid chromatography electrochemical detection methods. Methods Enzymol. 2001, 335, 15-26. 

Jin DR, Hakamata H, Takahashi K, Kotani A, Kusu E (2004) Separatimi of flavonoids by semi-micro high-pmformance liquid chrmnatography with electrochemical detection. B Chem Soc Jpn 77 1147—1152... 

Novak I, Janeiro P, Seruga M, Oliveira-Biett AM (2008) Ultrasound extracted flavonoids from foiff varieties of Portuguese red grape skins determined by reverse-phase high-performance liquid chromatography with electrochemical detection. Anal Chim Acta 630 107-115... 

The electroactive property of flavonoids was used to optimize a FIA coupled to an electrochemical detection (FIA-EC) method to determine quercetin and rutin natural plant extracts and pharmaceutical preparations [65]. In this method, flavonoids were determined at normal (unheated) and hot platinum microelectrodes using cyclic voltammetry. The use of the FIA system causes an increase of the analytical signal by more than 6 times because of the increase of the temperature to about 76°C in a small zone close to... 

Examples of electrochemical detection apphed to flavonoid analysis are presented in Table 3.10. Acceptable resolution of flavonoids has been achieved with LC working in isocratic conditions or with gradient elution, mainly consisting of two phases, ° in RP (C18) columns with electrochemical detector. 

Peng, Y., Liu, F., and Ye, J., Quantitative and qualitative analysis of flavonoids markers in Frucus aurantii of different geographical origin by capillary electrophoresis with electrochemical detection, J. Chromatogr. B, 830, 224, 2006. 

Procyanidins can usually not be completely separated from each other, from phenolic acids and from accompanying flavonoids by sample clean up and/or chromatographic procedures. The differentiation between these individual compounds can therefore only by accomplished by the selectivity of a suitable detection method. UV-DAD (ultra violet diode array detection), electrochemical and mass spectrometry detection have been used for the identification and quantitative determination of procyanidins. 

Multichannel electrochemical coulometric detection or coulometric array detection has been developed so that different potentials are applied on the electrodes. A number of chromatograms (8, 12, or 16) can be recorded simultaneously. Flavonoids can have several oxidation processes across the array of potentials, giving characteristic profiles for identification. Methods were developed for the... 

Although UV-Vis detector is the most widespread detection system, fluorescence or electrochemical detectors have also proven adequate for flavonoid analysis. However, the lack of active fluorescent or electrochemical groups in many flavonoids may affect the accuracy of these detection methods. MS is a powerful, highly sensitivity technique. Its use is spreading among food scientists because of its effectiveness in the identification of flavonoids and their applicability for quantitative analysis. Common sources of error in flavonoid analysis may derive from nonlinearity of the detector, which should be checked since many detectors are linear over only one or two decades. In addition, the different response factors of different flavonoids should be taken into account since detectors usually are not equally sensitive to aU components of a mixture. 

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