A mass spectrometry assay that combines two mass spectrometers together to analyze complex biomolecules such as peptides. The first instrument separates ionized molecules by their mass-to-charge ratio and filters for ions at a particular ratio. Once isolated, these ions are fragmented into smaller ions that are analyzed with the second instrument. The mass-charge filter and fragment spectra are then compared to a reference database to identify the original molecule. [ http://www.ncbi.nlm.nih.gov/pubmed/3462691 http://orcid.org/0000-0002-3564-4813 ]