Mass spectra of free amino acids

The difficulty in studying free amino acids by MS is their low volatility. The simplest mass spectrometers call for samples with a sufficient vapour pressure, which can often be attained with intractable samples by raising the temperature of the sample-inlet system. The trade-off when high-temperature ionisation is used is that against the thermal stability of the sample. This is the source of the problem, since extensive thermal degradation of free amino acids occurs when the simplest mass spectrometers are used with ion sources at high temperatures. 

The sort of information that more sophisticated instrumentation has provided relates to subtle structural details of free amino acids, such as intramolecular hydrogen bonding and intermolecular associations in the gas phase. These details are not really relevant to analytical work and are not covered here. 

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