Mass spectrometry is used to analyse complex mixtures of components where the amounts of sample available is limited so as to preclude isolation of the individual components.
The results of an experiment can be compared to libraries of compounds to positively identify them. It is both a quantitative and a qualitative technique. In complex biological systems where small molecules are analysed, this is referred to as Metabolomics.
Electron ionisation (EI)
When combined with gas chromatography complex mixtures can be analysed and compared to one of many libraries commercially available.
Chemical ionisation (CI)
A softer ionisation technique than electron ionisation that can also be combined to gas chromatography. A more reliable method to determine the molecular mass of an unknown.
Electrospray ionisation (ESI)
This technique is combined to a HPLC permitting the analysis of the outlet stream from a HPLC. Good for polar molecules.
Atmospheric pressure chemical ionisation (APCI)
Similar to ESI when combined to a HPLC however better results for less polar molecules.