TABLE OF CONTENTS The low volatility and polar character of biomolecules and biopolymers initially prevented their direct ionisation and analysis by mass spectrometry. These compounds could, at best, only be studied after derivatisation of their polar groups, through methylation and acetylation, or following their degradation by, for example, acid hydrolysis. This converts large biopolymers into manageable (and ionisable) smaller molecules. Even then, only low to moderate (~1000) molecular weight compounds could be introduced into a mass spectrometer in the form of gaseous ions.
This situation changed, first with the development of plasma desorption and fast atom bombardment, and subsequently with the introduction of the electrospray and matrix-assisted laser desorption ionisation techniques. ESI and MALDI are particularly proficient at ionising large biopolymers (to several hundred thousand Daltons) without any pre-treatment or degradation of the sample. These ionisation methods are highly complementary in terms of their performance and suitability to particular samples. As a consequence, most laboratories that study biological compounds by mass spectrometry possess at least two instruments, one with an ESI source and the other with a MALDI source. Alternatively an instrument that can support both ion sources interchangeably can be used.
Peptides, proteins, glycoproteins, glycoconjugates, glycolipids, lipids, oligonucleotides and moderately-sized nucleic acids can all be efficiently introduced into a mass spectrometer by virtue of the ESI and MALDI techniques. Their importance to the analysis of biological macromolecules was recognised in 2002 by the award of the Nobel Prize in Chemistry to those who contributed to their...
