Phenol electrochemical detection

Micellar gradient elution liquid chromatography with electrochemical detection with sodium dodecyl sulfate has been used to separate phenols [186]. 

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). 

Because LCEC had its initial impact in neurochemical analysis, it is not, surprising that many of the early enzyme-linked electrochemical methods are of neurologically important enzymes. Many of the enzymes involved in catecholamine metabolism have been determined by electrochemical means. Phenylalanine hydroxylase activity has been determined by el trochemicaUy monitoring the conversion of tetrahydro-biopterin to dihydrobiopterin Another monooxygenase, tyrosine hydroxylase, has been determined by detecting the DOPA produced by the enzymatic reaction Formation of DOPA has also been monitored electrochemically to determine the activity of L-aromatic amino acid decarboxylase Other enzymes involved in catecholamine metabolism which have been determined electrochemically include dopamine-p-hydroxylase phenylethanolamine-N-methyltransferase and catechol-O-methyltransferase . Electrochemical detection of DOPA has also been used to determine the activity of y-glutamyltranspeptidase The cytochrome P-450 enzyme system has been studied by observing the conversion of benzene to phenol and subsequently to hydroquinone and catechol... 

Long, H., Zhu, Y. X., and Kissinger, P. T. (2003). Liquid chromatography with multi-channel electrochemical detection for the determination of natural phenolic compounds. Chin. J. Anal. Chem. 31, 631-634. 

Sontag, G., Friedrich, O., Kainz, G., and Jorg, E. (1989). Determination of phenolic compounds by HPLC with electrochemical detection. Proc. EUR 5th Food Chem. Conference, Agric. Food Chem. Consum. 2, 703-707. 

High-performance liquid chromatographic separation with electrochemical detection may provide the best sensitivity for phenol quantification in biological samples. The use of gas chromatography with a flame ionization detector may be a more versatile method, if other non-ionic pollutants must be quantified. The advantages and disadvantages of different methods available for the quantification of phenol and metabolites in biological and environmental samples have been discussed by Tesarova and Packova(1983). 

Achilli G, Cellerino GP, d Eril GM, et al. 1995. Simultaneous determination of 27 phenols and herbicides in water by high-performance liquid chromatography with multi-electrode electrochemical detection. J Chromatogr 697 357-362. 

Nieminen E, Heikkila P. 1986. Simultaneous determination of phenol, cresols and xylenols in workplace air, using a polystyrene-divinylbenzene column and electrochemical detection. J Chromatogr 360 271-278. 

Paterson B, Cowie CE, Jackson PE. 1996. Determination of phenols in environmental waters using liquid chromatography with electrochemical detection. J Chromatogr 731 95-102. 

Pocurull E, Marce RM, Borrull F. 1996. Determination of phenolic compounds in natural waters by liquid chromatography with ultraviolet and electrochemical detection after on-line trace enrichment. J Chromatogr 738 1-9. 

In particular, the priority pollutant phenols (PPP), identified by EPA since the 1970s are widespread water pollutants that must receive the greatest attention due to their recognized toxicity. For the separation of eleven PPP, an ion-interaction reagent (HR) RP HPLC/UV method has been developed that allows limits of detection lower than 30 J,g in river waters, after LLE in dichlo-romethane and a 500-fold pre-concentration [82]. Through on-line SPE followed by both UV and electrochemical detection [83], 16 priority phenols have been determined in water samples with the LOD value for chlorophenols lower than 1 ng L [84]. LODs at ng L levels were obtained for all the PPPs in samples of river water, employing a relatively small volume of sample through an on-line SPE HPLC/MS method with an APCI source. 

A postchromatographic -glucuronidase procedure has been also used for the analysis of phenolic glucuronides, such as those produced from trimethoprim (274). The enzymatic analysis of these glucuronides provided the production of the corresponding phenolic compounds, which were measured by both UV and electrochemical detection. 

The variety of detection modes available for HPLC analysis that provide additional information about the eluent as it exits the column greatly facilitates unknown characterization. The majority of analytical methods for phenolic compounds includes HPLC with spectrophotometric-based detection techniques (UV absorption, fluorescence, photo diode array—PDA) as well as HPLC with electrochemical detection. 

HPLC-based electrochemical detection (HPLC-ECD) is very sensitive for those compounds that can be oxidized or reduced at low voltage potentials. Spectrophotometric-based HPLC techniques (UV absorption, fluorescence) measure a physical property of the molecule. Electrochemical detection, however, measures a compound by actually changing it chemically. The electrochemical detector (ECD) is becoming increasingly important for the determination of very small amounts of phenolics, for it provides enhanced sensitivity and selectivity. It has been applied in the detection of phenolic compounds in beer (28-30), wine (31), beverages (32), and olive oils (33). This procedure involves the separation of sample constituents by liquid chromatography prior to their oxidation at a glassy carbon electrode in a thin-layer electrochemical cell. 

G Chiavari, V Concialini, GC Galletti. Electrochemical detection in the high-performance liquid chromatographic analysis of plant phenolics. Analyst 113 91-94, 1988. 

Molecules which are not electrochemically active can be derivatized using an appropriate "electrophore", making the derivative eligible for electrochemical detection (9). It is fortunate that the nitrophenyl group, commonly used for UV and GC derivatization, is easily reducible. Methods based on the determination of intact carbamate residues by GC have been very disappointing as the result of thermal instability of a large majority of carbamate compounds. Therefore, a number of derivatization methods have been proposed. Carbamates, which produce an aromatic amine or phenol when hydrolyzed, were derivatized using 2,4-Dinitrofluorobenzene (DNFB) to form 2,4-... 

Typically, in gradient elution liquid chromatography, electrochemical detection has been difficult due to base-line shifts that result as a consequence of the altered mobile phase composition. However, a unique property of micelles allows for much improved compatibility of gradients (i.e. gradient in terms of micellar concentration or variation of small amount of additive such as pentanol) with electrochemical detectors. This has been demonstrated by the separation and electrochemical detection of phenols using micellar gradient LC (488). A surfactant (apparently non-micellar) gradient elution with electrochemical detection has also been successfully applied for the assay of some thyroid hormones by LC (491). 

Woodring, P. J. Edwards, P.A. Chisholm, M.G. 1990. HPLC determination of nonflavonoid phenols in Vidal Blanc wine using electrochemical detection. J. Agric. Food Chem. 38 729-732. 

Vanbeneden, N., Delvaux, E, Delvaux, ER. (2006). Determination of hydroxycinnamic acids volatile phenols in wort and beer by isocratic high-performance liquid chromatography using electrochemical detection. J. Chromatogr. A, 1136, 237-242. 

Knutsson M, Mathiasson L, and Jdnsson JA. Supported liquid membrane work-up in combination with liquid chromatography and electrochemical detection for the determination of chlorinated phenols in natural water samples. Chromatographia 1996 42 165-170. 

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