Determination of sulfite in sugar and sulfur dioxide in air by chemiluminescence using the Ru(bipy)3(2+)-KBrO3 system. Analyst

A chemiluminescence (CL) detection method for the determination of sulfite using the reaction of Ru(bipy)32+ (bipy = 2,2A-bipyridyl)–SO322–KBrO3 is described. The concentration of sulfite is proportional to the CL intensity in the range 2.5 3 1028–9.5 3 1025 mol l21. The limit of detection is 3.8 3 1029 mol l21 and the relative standard deviation is 4.6 % for 5 3 1025 mol l21 sulfite solution with nine repeated measurements. This method was successfully applied to the determination of sulfite in sugar and sulfur dioxide in air by using triethanolamine as the absorbent material. The determinations of sulfite and sulfur dioxide are very important because of their use as food preservatives to prevent oxidation and bacterial growth and a reducing agent in bleaching, they also show potential toxicity as pollutants in the atmosphere. Many methods are available for their determina-tion, such as spectrophotometry,1,2 potentiometry,3,4 coulo-metry,5 gas chromatography–chemiluminescence (CL),6 HPLC–fluorescence detection7 and ion chromatography.8 How-ever, each has some drawbacks, such as lack of sensitivity, selectivity or simplicity. CL has been used for the determination of sulfite because of its high sensitivity and simplicity. The CL was produced by sulfite as follows: sulfite can be oxidized by copper(ii)9 in an alkaline solution, and reacts with the chemiluminescent reagent luminol.10 In an acidic solution it can be oxidized by potassium permanganate11 or cerium(iv).12 The light-emission intensity can be enhanced by the presence of some compounds, e.g., riboflavin for reaction with permanga-nate13,14 and cerium(iv),15 flavin mononucleotide for reaction with permanganate16 and 3-cyclohexylaminopropanesulfonic acid (CAPS) for reaction with permanganate14,17 and cer-ium(iv),18 steroids for reaction with potassium bromate19 and sodium cyclamate for reaction with cerium(iv).20 The kinetics and mechanism of sulfite oxidation were as follows:9,2