Review on atmospheric pressure ionization sources for gas chromatography-mass spectrometry. Part I: Current ion source developments and improvements in ionization strategies

The use of atmospheric pressure ionization (API) sources has become very popular for gas chromatography-mass spectrometry (GC-MS) determinations. GC-API-MS shows important advantages over traditional vacuum ionization sources such as a lower fragmentation preserving the molecular or quasi-molecular ion, the combination of GC separations with advanced mass spectrometers typically developed for liquid chromatography (LC) systems, a significantly higher sensitivity, or the reduction of costs due to the capability to use the same MS for both LC- and GC- couplings. For these reasons, the development of new API sources and GC-API-MS platforms has exponentially increased during the last years. Thus, this review is mainly focused on the last advances in GC-API-MS instrumentation. New setups and couplings on extensively reported API techniques as well as the development of new API sources for GC-MS coupling are thoroughly discussed. Moreover, novel ionization strategies have been reviewed to overcome some of the drawbacks of GC-API-MS methodologies.