6. Qualitative analysis

6.1 Random search for a priori unknown molecules

The problem is analogous to "finding a needle in a haystack", without being sure it's there. It's best to separate all the constituents of the mixture and try to identify them one by one.

It's important to gather as much information as possible about the origin and possible composition of the mixture, as well as the analytical protocol preceding GC-MS. Apart from a few limited cases, no ionization method can identify a molecule solely on the basis of its mass spectrum. Identification is essentially based on the similarity between a spectrum extracted from GC-MS data and that of a molecule listed in a library of mass spectra. Additional data, such as prior information and chromatographic retention parameters, can...