Foodstuffs electrochemical detection

With the major constituents in foods the choice of LC detector is often the most important issue. Compounds such as vitamins, carbohydrates etc. may not have a strong ultraviolet (UV) chromophore. Therefore refractive index (RI) detection and, increasingly, electrochemical detection are often used. As discussed later, the choice of detector is even more important when determining the concentration of components in the foodstuff rather than the bulk constituent. 

Pachla, L.A. Kissinger, P.T. Determination of ascorbic acid in foodstuffs, pharmaceuticals, and body fluids by liquid chromatography with electrochemical detection. Anal. Chem. 1976, 48, 364-367. 

Electrochemical techniques found many fewer appfica-tions for the determination of total iodine in foodstuffs compared with other techniques. They are inexpensive, but their limited specificity requires careful validation of the procedures developed. On the other hand, electrochemical detection of iodine species separated by chromatographic methods seems to be well-established. 

Chiu, M.-H., Yang, H.-H., Liu, C.-H. and Zen, J.-M. (2009) Determination of lin-comycin in urine and some foodstuffs by flow injection analysis coupled with liquid chromatography and electrochemical detection with a preanodized screen-printed carbon electrode. J. Chromatogr. B, 877, 991-994. 

Ultimately major efforts to develop coupled chromatographic techniques have been performed to alleviate the problem of manual sample pretreatment and to enhance sensitivity and selectivity in the analysis of PAHs in foodstuffs (192) and environmental samples (193-195). Liquid chromatography/MS (196,197), GC/MS (175), HPLC with UV absorbance, fluorescence (177) (see Fig. 4), or electrochemical (ED) detection (179), and ELISA immunoassay (198) have been successfully used for the determination of HAAs. 

Bettazzi F, Lucarelli F, Palchetti I, Berti F, Marrazza G, Mascini M (2008). Disposable electrochemical DNA-array for PCR amplified detection of hazelnut allergens in foodstuffs. Anal. Chim. Acta, 614(1) 93-102. 

Spectroscopic, luminescence, turbidimetric, and electrochemical methods of detection have been combined with SIA for the successful determination of amino acids, sugars, and trace elements in matrices such as meats, vegetables, breads, wines, juices, and milks. Many of these methodologies required sample pretreatment and whilst most performed this in an offline manner there have been some reports of online sample cleanup. Microwave assisted digestion was performed in-line for the determination of phosphorous, calcium, magnesium, and iron in slurried foodstuffs, wine, milk, and soft drinks whilst gaseous diffusion allowed interference removal for the determination of urea in milk. 

Reversed-phase h.p.l.c. with appropriate on-line immobilized oxidase enzyme reactors and an electrochemical detector to determine the hydrogen peroxide generated, proved sensitive (nM to pM detection limits), selective and rapid, and was applicable to the analysis of sugars in foodstuffs or... 

Determination of vitamin B12 by LC—UV is difficult to perform in non-supplemented foodstuffs because of the very low concentrations of the vitamin and the poor sensitivity and selectivity of the detection s)istem employed. These problems were overcome using an immimoaffinity column and monitoring the vitamin at 361 run [58]. The extractive procedure of liebiedzihska et al. [7] was based on an enzymatic digestion with a-amilase and papain after autoclaving salmon samples at 121°C in the presence of cyanide cyanocobalamin was monitored by an electrochemical detector. 

Bettazzi et al. used an electrochemical low-density DNA array in combination with polymerase chain reaction (PCR) in order to investigate the presence of hazelnut major allergens. Cor a 1.04 and Cor a 1.03, in foodstuff. Unmodified PCR products were captured at the electrode interface via sandwich hybridization with surface-tethered probes and biotinylated signaling probes. The resulting biotinylated hybrids were coupled to a streptavidin-alkaline phosphatase conjugate and then exposed to an a-naphthyl phosphate solution. Differential pulse voltammetry (DPV) was used to detect the a-naphthol signal with detection limits as 0.3 and 0.1 nmol for Cor a 1.03 and Cor 1.04, respectively. The results are comparable with the ones obtained with classical ELISA tests. 

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