Analytical Methods Pervaporation flow injection analysis for the determination of sulphite in food samples utilising potassium permanganate–rhodamine B chemiluminescence detection Sakchai Satienperakul a, * , Pornthana Phongdong a , Saisunee Liawruangrath b a Department of Chemistry, Faculty of Science, Maejo University, Chiang Mai 50290, Thailand b Department of Chemistry and Centre for Innovation in Chemistry, Postgraduate Education and Research Program in Chemistry (PERCH-CIC), Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand article info Article history: Received 14 July 2009 Received in revised form 1 January 2010 Accepted 16 January 2010 Keywords: Sulphite Flow injection Pervaporation Chemiluminescence Acidic potassium permanganate Rhodamine B abstract A simple pervaporation flow injection chemiluminescence (PFI-CL) procedure was utilised as an on-line separation for the analysis of contaminated sulphite in food samples. The method involves the injection of standard and/or sulphite sample solutions into a 0.20 M sulphuric acid donor stream. Sulphite is con- verted to sulphur dioxide and transported to the donor chamber of a pervaporation module. The sulphur dioxide gas then evaporates into the headspace and diffuses across a semi-permeable PTFE membrane into an acceptor stream containing 0.75% (m/v) sodium hexametaphosphate and 1.0 mg L À1 rhodamine B in 0.02 M H 3 PO 4 , which functions as a carrier solution for the chemiluminescence detection. The sul- phur dioxide in the acceptor stream merges at a T-piece with a reagent stream consisting of potassium permanganate (8.0 10 À5 M) prepared in the acidic sodium hexametaphosphate carrier solution. The elicited chemiluminescence intensity of the resulting reaction mixture was measured at a red sensitive photomultiplier tube operated at a voltage of 1.00 kV. Optimal experimental conditions for an on-line determination of sulphite were investigated. The second-order polynomial calibration curve was devel- oped over the concentration range of 0.5–10.0 mg L À1 sulphite with a resulting equation of I = À0.239C 2 + 4.846C À 1.64, r 2 = 0.9997. The detection limit was found to be 0.2 mg L À1 with a sampling frequency of 30 h À1 . The effects of common anionic and cationic interferences were also investigated. The proposed PFI procedure was successfully applied to the determination of sulphite in different food sam- ples. The PFI data was validated versus standard differential pulse polarography. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Sulphiting agents (sulphur dioxide, sulphite, hydrogensulphite and metabisulphite) are commonly used as an additive in several foods and beverages for various purposes; e.g. to inhibit undesir- able micro-organisms in fermentation industries, to control enzy- matic and non-enzymatic browning reactions, and to assist in preserving vitamin C (Hanssen, Marsden, & Norris, 1989). Sulphite has been reported to cause harmful effects in hypersensitive peo- ple, exhibiting a wide variety of symptoms from hives, nausea and diarrhoea to respiratory failure and asthmatic attacks. Hence, products containing more than the established threshold sulphite level should be labelled adequately. The US Food and Drug Admin- istration (FDA) requires sulphite declaration on the label of any food in concentrations of 10 lg mL À1 sulphite or more (Warner, Diachenko, & Bailey, 2000). This obligation is also compulsory for pre-packed food sold in the UK and the rest of the European Union (Food Standards Agency, 2005/2006). The Association of Official Analytical Chemists (AOAC, 1990) standard detection method involves an iodimetry or gravimetry (detects sulphate) or polarographic procedure for sulphite deter- mination in foods and beverages. These procedures require an acid distillation to isolate gaseous sulphur dioxide from sample matri- ces prior to analysis. Normally, the conventional titrimetric meth- od suffers from poor precision and large time consumption during the acid distillation step, while the polarographic chemicals are highly toxic and harmful. Although the official methods are available to determine sulph- ite and sulphur dioxide in food samples, newer methods appear in recent literature. One especially searches for a simple and sensitive method which can be used for a broad range of complex samples (Ruiz-Capillas & Jiménez-Colmenero, 2009) and which can be eas- ily automated for an on-line separation. Gas diffusion flow injec- tion analysis (GD-FI) is one choice for determining sulphite and sulphur dioxide in food and beverages. This method is based on 0308-8146/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2010.01.013 * Corresponding author. Tel.: +66 53 873544; fax: +66 53 878225. E-mail address: sakchais@mju.ac.th (S. Satienperakul). Food Chemistry 121 (2010) 893–898 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem