Ion Chromatographic Determination of Sulfur Dioxide in Foods

Abstract

An ion chromatographic (IC) method was developed for the determination of sulfur dioxide in foods. Sulfur dioxide was separated from a food sample by addition of acid and heating, and carried into a trapping solution by bubbling. Conditions for separation and trapping of sulfur dioxide were as follows: sample, 1-5g; acid, 40ml of 20% phosphoric acid deaerated with nitrogen for 10min; heating temp., 90°C; bubbling gas, nitrogen; flow rate, 800ml/min; bubbling time, 40min; trapping solution, 10ml of 1% triethanolamine solution. After bubbling, the trapping solution was subjected to IC. Sulfite was separated on an anionic separator column, “SAX-1” with 3.5mM Na2CO3/4.0mM NaHCO3 as the eluent and quantitated by the use of a conductivity detector.In the determination of sulfur dioxide in foods by IC, nitrite ion and volatile aldehydes interfered. Thus, 1ml of 1% ammonium sulfamate solution was added the sample to eliminate nitrite and 5ml of 40% phosphoric acid containing 1% 2, 4-dinitrophenylhydrazine was placed between the trapping solution and the cooling condenser to eliminate aldehydes.The recoveries of sulfur dioxide added to water and 6 foods at levels of 10 and 100μg/g were 87.8-109.0% and, 97.3-104.7%, respectively. The detection limit was 0.2μg/g in the case of a 5g sample size.The proposed method, gas chromatography after separation and trapping by bubbling (bubbling-GC method) and the modified Rankine colorimetric method (MR method) were all applied to the determination of sulfur dioxide in commercial foods and the results were compared. The values of residual sulfur dioxide obtained from the foods treated with sulfite by all three methods were in good agreement. The values of naturally occurring sulfur dioxide obtained from the foods containing sulfur compounds without sulfite treatment by the proposed method and the bubbling-GC method were in good agreement, although those obtained by the MR method were higher.