A rapid and simple UHPLC-ESI-MS/MS method for the screening of propyl propane thiosulfonate, a new additive for animal feed
Allium derivative propyl propane thiosulfonate (PTSO) is a new additive for animal feed which improves animal health when used as an alternative to antibiotic growth promoters. Despite the effort of the European Union to ensure the control of animal feed alterations, information available on this new additive is sparse and analytical methods used for its monitoring have limited reach. Moreover, existing analytical methods exhibit shortcomings when applied to other matrices or when attempting to measure low concentration levels. This paper describes for the first time that PTSO reacts instantaneously with cysteine (CYS) and glutathione (GLU) generating s-propyl mercaptocysteine (CSSP) and s-propyl mercaptoglutathione (GSSP), thus explaining the limitations of previous methods when applied to feed with high concentration levels of CYS and GLU. Therefore, an ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method combined with a sample treatment based on simple solid–liquid extraction with methanol is proposed for the monitoring of PTSO, CSSP and GSSP in a wide range of animal feed samples including those for pigs, piglets, broilers, hens, rabbits and partridges. This method provides a simple, robust and efficient alternative for the determination of this additive. Matrix-matched calibration curves were established for PTSO, CSSP and GSSP and limits of detection (LODs) and quantification (LOQs) were estimated, being lower than the ones previously reported for PTSO when using HPLC-UV. The relative standard deviation of the whole analytical method was lower than 10% in all cases, while recoveries ranged from 93% to 104%.