Nowadays the molecular weights of intact proteins of several tens of kDa can be determined very precisely by mass spectrometry and even the determination of the molecular weight of a coliphage T4 DNA species of about 100 MDa has been shown to be possible. Simultaneously instrumental developments have taken place which permit to study the chemistry of species within the vacuum of the mass spectrometer in great detail. The knowledge obtained in this way is amongst others important to be able to extract information from mass spectral data in terms of chemical structures or to understand what happened in chemical reactions.
Actually, the sophistication of high performance mass spectrometers has reached such a level that they can be considered as complete laboratories by themselves. That is, following generation of ions (synthesis) species with a particular m/z subsequently can be selected (purified), modified (derivatised) and brought into reaction with suitable substrates (chemical reaction), whereafter the ionic reaction products are detected and analysed (product analysis). This enables, for example, to study in detail the reactivity and hydrogen/deuterium exchange behaviour of mass selected ions in reactions with suitable substrates and to determine quantitatively thermodynamic properties of reactive and/or kinetically unstable species as will be exemplified in the lecture.