Glassy Carbon Electrode Modified with Functionalized Carbon Nanotubes Within a Poly(allylamine hydrochloride) Film for the Voltammetric Determination of Sulfite in Foods Elen Rom¼o Sartori, a Humberto Hissashi Takeda, b Orlando Fatibello-Filho * a, c a Departamento de Química, Universidade Federal de S¼o Carlos, C.P. 676, 13.560-970, S¼o Carlos – SP, Brazil b Departamento de Engenharia de Alimentos, Fundażo Universidade Federal de Rondônia, 76872-862, Ariquemes – RO, Brazil c Instituto Nacional de CiÞncia e Tecnologia de Bioanalítica (INCT de Bioanalítica) *e-mail: bello@ufscar.br Received: May 3, 2011; & Accepted: June 15, 2011 Abstract The performance of a glassy carbon electrode modified with functionalized multiwalled carbon nanotubes within a poly(allylamine hydrochloride) film (GCE/PAH/MWCNTs) for the voltammetric determination of sulfite in food samples is described. The anodic peak potential for sulfite oxidation at a GCE/PAH/MWCNTs was 0.41 V whereas at GCE/PAH and GCE, the peak potentials were 0.96 and 0.89V, respectively. Using square-wave voltammetric technique, the obtained analytical curve was linear in the sulfite concentration range from 1.1 10 5 to 3.9  10 4 M, with a detection limit of 4.2 mM. The electrode was successfully used to determinate sulfite in vinegar, pickle water, coconut water, and shredded coconut. Keywords: Glassy carbon electrode, Multiwalled carbon nanotubes, Modified electrode, Poly(allylamine hydrochloride), Sulfite determination DOI: 10.1002/elan.201100122 1 Introduction Sulfites or sulfating agents have been used as additives (E220–E228) in food and beverages [1] in order to pre- vent oxidation, inhibit growth of bacteria, and control en- zymatic and nonenzymatic reactions, thereby enhancing the appearance and flavor of many foods during their preparation, storage, and distribution stages [2]. As food additives they include sulfur dioxide, sodium sulfite, sodium and potassium hydrogen sulfite, and sodium and potassium metabisulfite, among others. They are all chemically equivalent (SO 2 , HSO 3  , SO 3 2 and S 2 O 5 ) after incorporation into food and beverage at a given pH. Many foods and beverages that people consume on a regular basis contain sulfite and its content should be strictly limited due to its potential toxicity and harmful effects in humans, particularly hypersensitivity, such as nausea, diarrhea, gastric irritation, nettle rash or swelling, and asthma attacks [3]. Dried fruits and vegetables, pick- les, coconut water, vinegar, juices, and wine are among the foods and beverages containing sulfite. Sulfite levels in food vary widely depending on the products. In several countries the use of sulfite is subject to regulations, which establish permitted levels of use and include labeling re- quirements. The Food and Drug Administration (FDA) requires that the presence of sulfite containing more than 10 mg kg 1 or 10 mg L 1 in processed foods to be declared on the label [4]. The acceptable daily intake of sulfite (expressed as SO 2 ) is 0.7 mg kg 1 body weight, including all species containing S(IV) [5]. The National Health Sur- veillance Agency (ANVISA) monitors the safety of food additives in Brazil and then sets legal limits on the levels of these additives in many different foods, including vine- gar, coconut water, shredded coconut (200 mg L 1 ), and pickles (100 mg L 1 ) [6]. As food safety is of paramount importance, the development of an accurate analytical procedure that allows an assessment of the quality of manufactured products containing sulfite is mandatory to verify whether the product meets its quality require- ments. Distillation of the samples under acidic conditions and then titration [7], photometry [8] and iodometry [9] are the traditional and official methods for sulfite determina- tion in foods and beverages. A major limitation of iodo- metric titration [9] protocols is that they are only suitable for uncolored samples, since the end-point is detected by the formation of the blue-like starch-iodine complex. The Monier-Williams procedure still remains the method of choice [10]. It offers sufficient sensitivity, but is tedious, time-consuming, and suffers moreover from much possi- ble interferences such as from reducing species frequently present in real samples. Several methods for the analytical determination of sul- fite have been reported in the literature, such as conduc- tometry [11], spectrophotometry [12] chemiluminescence [13], and capillary electrophoresis [14]. However, these 2526  2011 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim Electroanalysis 2011, 23, No. 11, 2526 – 2533 Full Paper