Sensitive Determination of Four Polypeptide Antibiotic Residues in Milk Powder by High Performance Liquid Chromatography–Electrospray Tandem Mass Spectrometry

Polypeptide antibiotics abuse can lead to antibiotic residues in food products and have unwanted effects on human health. A selective, accurate, and sensitive analytical method for the simultaneous determination of four polypeptide antibiotics (gramicidin S, bacitracin, polymyxin B, and polymyxin E) in infant formula powder was developed using solid-phase extraction (SPE) combined with high performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS). The samples were extracted with acidified methanol, deproteinized with acetonitrile, and degreased with n -hexane before SPE. After cleanup with 0.1% formic acid and methanol (3:1, v/v) in Oasis HLB cartridges, the extracts were analyzed by HPLC–MS/MS with electrospray ionization (ESI) source and time-scheduled multiple reaction monitoring (MRM). Linearity was assessed by using matrix-matched standard calibration and good determination coefficients ( r 2 > 0.995) were obtained. The average recoveries for blank sample at three spiked concentration levels were in the range of 82.8–101.2%. The limits of detection (LODs) and limits of quantitation (LOQs) of all analytes were in the range of 5–15 μg kg −1 and 20–50 μg kg −1 , respectively. The intra-day and inter-day precisions were lower than 10%. The results of method validation demonstrated that the developed method is accurate and reliable, and it can be applied for screening and quantitation of target polypeptide antibiotics in food. Graphic Abstract