Applications of Tandem Mass Spectrometry: From Structural Analysis to Fundamental Studies

Abstract

1.1 Mass spectrometry brief history and recent developments The first and most important question to be asked: What is mass spectrometry? The basic principle of mass spectrometry (MS) is to generate ions from either inorganic or organic compounds by any suitable method, to separate these ions by their mass-to-charge ratio (m/z) and to detect them qualitatively and quantitatively by their respective m/z and abundance. The analyte may be ionized thermally, by electric fields or by impacting energetic electrons, ions or photons. The ... ions can be single ionized atoms, clusters, molecules or their fragments or associates. Ion separation is effected by static or dynamic electric or magnetic fields.(Gross 2004) Although this definition dates back to 1968, when mass spectrometry was at its childhood, it is still valid. Nevertheless, two additions should be included. Firstly, besides electrons, (atomic) ions or photons, energetic neutral atoms and heavy cluster ions can also be used to ionize the analyte. Secondly, ion separation by m/z can be effected in field free regions, as effectively demonstrated by the time-of-flight analyser, provided the ions possess a welldefined kinetic energy at the entrance of the flight path. From the 1950s to the present, mass spectrometry has evolved tremendously. The pioneering mass spectrometrist had a home-built naked instrument, typically a magnetic sector instrument with electron ionization. Nowadays, highly automated commercial systems, able to produce thousands of spectra per day, are now concealed in a “black box”, a nicely designed and beautifully coloured unit resembling more an espresso machine or tumble dryer than a mass spectrometer. Mass spectrometry (MS) is probably the most versatile and comprehensive analytical technique currently available in the chemists and biochemists arsenal. Mass spectrometry measures precisely the molecular masses of individual compounds by converting them into ions and analysing them in what is called a mass analyser. This is the simplest, but somewhat reductionist, definition of mass spectrometry. The days of the simple determination of the m/z ratio of an organic compound are over. Today, mass spectrometry can be used to determine molecular structures, to study reaction dynamics and ion chemistry, to provide thermochemical and physical properties such as ionization energy, appearance energy, reaction enthalpies, proton and ion affinities, gas-phase acidities, and so on.