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Abstract: The present review focuses on electrochemical methods for ascorbic acid assessment. The occurence, role, biological importance of vitamin C, as well as the non-electrochemical methods for its assessment are firstly reviewed. The electrochemical behavior of ascorbic acid is then illustrated, followed by a description of the potentiometric, voltammetric and amperometric methods for vitamin C content estimation in various media. Different methods for the development of electrochemical sensors are reviewed, from unmodified electrodes to different composites incorporating carbon nanotubes, ionic liquids or various mediators. From this perspective, the interaction between the functional groups of the sensor's material and the analyte molecule is discussed, as it is essential for the analytical characteristics obtained. The analytical performances of the potentiometric, voltammetric or amperometric chemical and biochemical sensors (linear range of analytical response, sensitivity, precision, stability, response time etc) are highlightened. The numerous applications of ascorbic acid electrochemical sensors in fields like food, pharmaceutical or clinical analysis, where vitamin C represents a key analyte, are also presented. [Copyright &y& Elsevier]

Antioxidants are compounds that prevent or delay the oxidation process, acting at a much smaller concentration, in comparison to that of the preserved substrate. Primary antioxidants act as scavenging or chain breaking antioxidants, delaying initiation or interrupting propagation step. Secondary antioxidants quench singlet oxygen, decompose peroxides in non-radical species, chelate prooxidative metal ions, inhibit oxidative enzymes. Based on antioxidants' reactivity, four lines of defense have been described: Preventative antioxidants, radical scavengers, repair antioxidants, and antioxidants relying on adaptation mechanisms. Carbon-based electrodes are largely employed in electroanalysis given their special features, that encompass large surface area, high electroconductivity, chemical stability, nanostructuring possibilities, facility of manufacturing at low cost, and easiness of surface modification. Largely employed methods encompass voltammetry, amperometry, biamperometry and potentiometry. Determination of key endogenous and exogenous individual antioxidants, as well as of antioxidant activity and its main contributors relied on unmodified or modified carbon electrodes, whose analytical parameters are detailed. Recent advances based on modifications with carbon-nanotubes or the use of hybrid nanocomposite materials are described. Large effective surface area, increased mass transport, electrocatalytical effects, improved sensitivity, and low detection limits in the nanomolar range were reported, with applications validated in complex media such as foodstuffs and biological samples. [ABSTRACT FROM AUTHOR]

• The development of ratiometric fluorescent probes led to improved specificity in sulfite assay. • Associating ion chromatography with other techniques (inductively coupled plasma / mass spectrometry) can lower the limit of detection. • Mediators hinder interferences by lowering the electro-oxidation potential in chemical sensors and enzyme sensors. • Nanoparticle-based sensors and biosensors enhance sulfite electroactivity, circumventing the oxidation of interfering species. • Conductive polymer films and screen printed sensors allow facile biocatalyst incorporation and improve electroactivity. Sulfite is a largely used preservative, and represents an analyte of interest, whose level should be carefully monitored, given the implications of its use, on human health. The present paper reviews the analytical techniques applied to sulfite quantification: titrimetric, spectrometric, chromatographic, electrochemical (voltammetric, amperometric, potentiometric). The methods are detailed with respect to their analytical performances (precision, accuracy, sensitivity), including modification of techniques aiming at improving selectivity, sensitivity, rapidity. A series of developed chemical sensors and biosensors aim at minimizing interferences from other electroactive compounds (mainly phenolics and ascorbic acid). The techniques' validation on real samples is discussed, with emphasis on food products and water analysis. The final section encompasses a critical and comparative discussion on the methods' appropriateness and performances. Image, graphical abstract [ABSTRACT FROM AUTHOR]