Analysis of antimicrobial agents in pig feed by liquid chromatography coupled to orbitrap mass spectrometry

The emerging trend towards full scan mass spectrometry alternatives was evaluated for the identification of a wide range of anti-bacterial compounds in animal feed. The high resolving power of the orbitrap exactive provides precise mass accuracy, resulting in high selectivity which enables qualitative and quantitative analysis in complex matrices such as feed. A simple generic sample preparation procedure was applied, including extraction of the feed samples with a combination of organic solvents. The mass spectrometer was operated in full scan with polarity switching between positive and negative modes, using heated electrospray ionization (H-ESI). The detection was carried out using automatic control of the number of ions entering the mass analyzer and with the combination of the ion injection time, accurate quantitative analysis was achieved. Due to the complexity of the feed samples the resolving power proved to be the key for the discrimination between interfering masses from the matrix and the exact masses of the compounds in order to achieve mass accuracy of 5 ppm. Furthermore, the use of narrow mass windows (±5 ppm) improved the selectivity of the method, increasing the signal-to-noise ratio for the compounds. A thoroughly validation study was successfully performed and evaluated in pig feed. The utilization of liquid chromatography to the high resolution orbitrap exactive proved to be a powerful tool for routine analysis of undesirable anti-bacterial compounds in feed control, ensuring food safety under the EU food chain legal framework.