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Detection of Lipids Using Direct Analysis in Real Time Mass Spectrometry

There has been a recent trend in mass spectrometry towards the development of “open-air” ionization sources. These techniques allow for the rapid analysis of samples at atmospheric pressure with little or no sample preparation. The Direct Analysis in Real Time (DART™) ion source, which is ideal for the analysis of small molecules, represents the first and simplest of the open-air techniques.1 This source creates ions based on the interactions of long-lived excited state neutral atoms or molecules (“metastables”) with the sample and atmospheric gases.

Figure 1 shows a schematic of the DART™ source. Samples are typically placed in a stream of helium or nitrogen containing these metastables (sample gap in Figure 1), which results in the formation of ions that are introduced into the mass spectrometer vacuum system through an orifice. Different ionization mechanisms occur depending on the type of sample being analyzed (and its concentration), the nature of the carrier gas used, and the polarity of the ions formed. A complete discussion of these mechanisms can be found elsewhere.

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