An isocratic HPLC technique is described for the determination of benzoic acid and sorbic acid in industrial quince jam. The preparation procedure was optimized. Precipitation of proteins and fat by the addition of methanol, followed by centrifugation and/or filtration provided an extract suitable for chromatographic analysis. The chromatographic separation was achieved with a C18 column and acetate buffer (pH = 4.4) - methanol (65:35) as the mobile phase. The effluent was monitored at 235 nm. Effective separation and quantification was achieved in less than 7 min. Specificity of the method was checked against common food additives added to industrial quince jam, such as L-ascorbic acid and citric acid. Diode array detection was used for confirmation of the preservatives. Mean recoveries of 95-104% were obtained with a precision less than 2.6%, detection limits of 25 and 6.25 mg/kg were obtained for benzoic and sorbic acids, respectively. Results were in good agreement with the reference methods. The presence of benzoic and sorbic acids in quince jams available on the Portuguese market, was also determined. Eleven commercial brands of quince jam were analysed. All contained benzoic acid. The concentration ranged from 413.9 ± 10.4 to 1501 ± 4.2 mg of benzoic acid/kg of quince jam. Only two brands also contained sorbic acid. The concentrations were 515.0 ± 7.0 and 908.3 ± 5.3 mg of sorbic acid/kg of quince jam. (C) 2000 Elsevier Science Ltd.
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