Institute of Food Research 1 article published in JoVE Biochemistry Species Determination and Quantitation in Mixtures Using MRM Mass Spectrometry of Peptides Applied to Meat Authentication Yvonne Gunning1, Andrew D. Watson1, Neil M. Rigby2, Mark Philo1, Joshua K. Peazer1,3, E. Kate Kemsley1 1Analytical Sciences Unit, Institute of Food Research, 2Institute of Food Research, 3School of Chemistry, University of East Anglia We present a protocol for identifying and quantifying the components in mixtures of species possessing similar proteins. Mass spectrometry detects peptides for identification, and gives relative quantitation by ratios of peak areas. As a tool food for fraud detection, the method can detect 1% horse in beef.