Sulfite, determination

Electrocatalysis in oxidation has apparently first been shown for ascorbic acid oxidation by Prussian blue [60] and later by nickel hexacyanoferrate [61]. More valuable for analytical applications was the discovery in the early 1990s of the oxidation of sulfite [62] and thiosulfate [18, 63] at nickel [62, 63] and also ferric, indium, and cobalt [18] hexacyanoferrates. More recently electrocatalytic activity in thiosulfate oxidation was shown also for zinc [23] hexacyanoferrate. Prussian blue-modified electrodes allowed sulfite determination in wine products [64], which is important for the wine industry. 

T. Garcia, E. Casero, E. Lorenzo, and F. Pariente, Electrochemical sensor for sulfite determination based on iron hexacyanoferrate film modified electrodes. Sens. Actuators B chem. 106, 803 (2005). 

Experimentally, Equation 15 was found to hold in a range of sulfite concentrations between 0.001 M and 0.050 M. The precision and accuracy of the sulfite determination was 2%. 

The concentration of sulfite in wine is expected to be in the low ppm range however, the sample matrix includes a wide variety of materials including several carboxylic acids, ethanol, sugars, and many other components. A search of the literature for sulfite determinations by ion chromatography yielded several references [1-22] describing a variety of separation methods, matrixes, and detection methods. Detection methods included ICP-AE [1], amperometric [3,5,9] refractive index [17], fluoro-metric [8,14] UV [12] and other methods. The sample type ranged from vitamins... 

The application of immobilized sulfite oxidase in the Multipurpose Bioanalyzer (Provesta, USA) has been described by Smith (1987). 1.8 U of the enzyme was entrapped in a gel at the active tip of an oxygen probe. The sensor is suitable for sulfite determination in food samples down to 100 ppm and has a lifetime of 84 days. 

M. Kato, M. Yamada, and S. Suzuki, Flavin Mononucleotide Sensitized and Polyoxyethylene (20) Sorbitan Trioleate Micelle-Enhanced Chemiluminescence for Sulfite Determination by Flow Injection Method [in Japanese]. J. Flow Injection Anal., 1(2) (1984) 31. 

Benzidine hydrochloride solution (for sulfite determination). Make a paste of 8 g of benzidine hydrochloride (Ci2Hg(NH3)2-2HCl) and 20 mL of water, add 20 mL of HCl (sp. gr. 1.12) and dilute to 1 L with water. Each mL of this solution is equivalent to 0.00357 g of H2SO4. 

Adeloju, S.B., S.J. Shaw, and G.G. Wallace. 1994. Polypyrrole-based amperometric biosensor for sulfite determination. Electroanalyis 6 865. 

Various different extraction conditions (distillation, acid extractant, alkaline extractant, etc.) have been tried for determination of sulfites in foods and beverages. These processes require some procedure to remove and recover the total sulfites (free and reversibly bound) and avoid loss of sulfites during extraction, which can be substantial. This is especially important in complex food matrices where extraction is a crucial step in sulfite determination. 

FIGURE 8.1 FIA diagram for sulfite determination (P pump Rl, R2 reactors). (Adapted from Ruiz-Capillas, C. and F. Jimenez-Colmenero. 2009. Food Chem. 112 487-493.)... 

The acceptor stream, where the released SO2 is collected, is usually a solution containing an acid-base indicator. The SO2 gas released from the donor diffuses through the membrane and is dissolved into the acceptor solution. Which acceptor is used (iodine, bromocresol green, malachite green, etc.) in sulfite determination depends on the detection system concerned (spectrophotometry, fluorometry, amperometry, etc.) (Figures 8.1 and 8.2). 

There have been studies on interferences in this system of SO2 determination with gas diffusion, chiefly in connection with the presence of compounds in beverages that are able to pass through the permeable membrane, such as nitrite, sulfide and cyanide (Frenzel and Hillmann, 1995). No interferences were detected with concentrations of nitrite up to 3 times higher than those of sulfite. Cyanine interference became apparent only when present at concentrations above 10 mg/L (Frenzel and Hillmann, 1995). In some cases, EDTA has been assayed as a means of preventing interference from some cations and anions however, it was found that EDTA practically doubled the sensitivity of the sulfite determination (Safavi and Haghighi, 1997). 

A copper electrode in an alkaline medium with amperometric detection has been used for sulfite determination in beverages (Corbo and Bertotti, 2002). Other systems have been reported such as a potentiometric sensor with a hydrated titanium oxide anion exchanger and an epoxy resin matrix membrane (Hassan et al., 2001) enzymes (sulfite... 

Some anionic surfactants are prepared using sulfite compounds. Such products are analyzed for residual sulfite ion. The standard method for sulfite determination is iodometric titration. Determination of sulfite in a-olefin sulfonates presents special problems, covered in detail by Perm and Griffin (29). 

Dadamos TRL, Teixeira MFS (2009) Electrochemical sensor for sulfite determination based on a nanostmctured copper-salen film modified electrode. Electrochim Acta 54 (19) 4552 558. doi 10.1016/j.electacta.2009.03.045... 

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