Direct ionization methods in mass spectrometry: An overview

•Positioning of direct spray mass spectrometric techniques as a sub-group of ambient ionization mass spectrometry.•Comprehensive overview of paper spray mass spectrometry applications published so far.•Comprehensive overview of tissue spray mass spectrometry applications published so far.•Comprehensive overview of other direct spray mass spectrometry applications published so far.

Within this paper a sub-group of ambient ionization mass spectrometry namely direct ionization mass spectrometry techniques are reviewed. They are characterized by the generation of an electrospray directly from the sample investigated. Prominent representatives include paper spray mass spectrometry, tissue spray mass spectrometry, probe electrospray ionization or thin-layer chromatography mass spectrometry. Applications of all major direct ionization techniques within different fields such as biomedical analysis, analysis of natural products, analysis of technical products and food analysis, just to name a few, are discussed and relevant parameters are listed in five Tables.

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