Learning Objectives This chapter will define construction and use of multiple types of mass spectrometers including GCMS and LCMS systems. Interpretation of the resulting data will be an important focus. describe the design of differing types of mass spectrometers explain how gas chromatography and liquid chromatography are used in tandem with mass spectrometers explain common ionization methods describe the function of common mass analyzers interpret mass spectra 2.1: Introduction to Mass Spectrometry Individual molecules often fall apart during the mass spectrometry experiment. As a result, in addition to measuring the mass of an entire molecule, we also obtain the weights of various smaller pieces of the molecule. That may add some confusion to the data. However, these fragments provide an idea about what parts make up the whole molecule. 2.2: Mass Spectrometry Mass spectrometry (MS) is a powerful characterization technique used for the identification of a wide variety of chemical compounds. At its simplest, MS is merely a tool for determining the molecular weight of the chemical species in a sample. However, with the high resolution obtainable from modern machines, it is possible to distinguish isomers, isotopes, and even compounds with nominally identical molecular weights. Libraries of mass spectra have been compiled which allow rapid identification 2.3: How the Mass Spectrometer Works This page describes how a mass spectrum is produced using a mass spectrometer. Electrospray Ionization Mass Spectrometry Injection Stage MALDI-TOF Mass Analyzers (Mass Spectrometry) 2.4: Interpretation of Mass Spectra 13C Br and Cl Fragmentation Fragmentation Patterns in Mass Spectra Molecular Ions Molecular Ion and Nitrogen Organic Compounds Containing Halogen Atoms The Molecular Ion (M⁺) Peak The M 1 Peak 2.5: Mass Spectrometry Problems LEGO Exercise 2.6: ESI-QTOF-MS Coupled to HPLC and its Application for Food Safety Mass spectrometry (MS) is a detection technique by measuring mass-to-charge ratio of ionic species. The procedure consists of different steps. First, a sample is injected in the instrument and then evaporated. Second, species in the sample are charged by certain ionized methods, such as electron ionization (EI), electrospray ionization (ESI), chemical ionization (CI), matrix-assisted laser desorption/ionization (MALDI).