article 180 mass spectrometry 138 nonhuman 124 unclassified drug 101 priority journal 93 controlled study 83 Mass spectrometry 77 chemistry 74 Animals 59 metabolism 50 Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization 46 electrospray mass spectrometry 46 matrix assisted laser desorption ionization time of flight mass spectrometry 45 Article 43 proton nuclear magnetic resonance 42 human 41 Humans 39 Spectrometry, Mass, Electrospray Ionization 35 Mass Spectrometry 33 Magnetic Resonance Spectroscopy 32 chemical structure 32 high performance liquid chromatography 30 nuclear magnetic resonance spectroscopy 29 animal 28 Argentina 27 carbon nuclear magnetic resonance 27 drug structure 27 Molecular Structure 26 Chromatography, High Pressure Liquid 24 drug isolation 24