Development of a LC-MS/MS method for the simultaneous determination of sorbic acid, natamycin and tylosin in Dulce de leche

A simple extraction, rapid routine method for the simultaneous determination of sorbic acid, natamycin and tylosin in Dulce de leche, a traditional South American product, by liquid chromatography-tandem mass spectrometry has been developed and fully validated. The limits of detection were set to 24.41mgkg(-1) (sorbic acid), 0.10mgkg(-1) (natamycin) and 2μgkg(-1) (tylosin). Recoveries ranged from 95% to 110%. Proportionally, internal standardization was more efficient than external standard, resulting in a smaller measurement of uncertainty. In total, 35 commercial samples from Brazil, Argentina and Uruguay have been assessed. The proposed method was tested on other dairy desserts, demonstrating to be versatile. Although tylosin was not detected in any sample, a high rate of non-compliance was found, with 67.39% of samples above the maximum allowed for sorbic acid and a maximum concentration of 2105.36±178.60mgkg(-1). In two samples, natamycin was irregularly found.