The relevant role of humidity in Secondary Electrospray Ionization (SESI)

Rising the humidity level of the gas introduced through the sample line accelerates the charge transfer reaction rate in Secondary Electrospray Ionization (SESI). It is hypothesized that larger clusters transfer their charge more efficiently than smaller clusters or even bare ions. A study introducing regular and deuterated ethanol and water in the sample gas, showed that the gas-phase proton-affinity of the molecules clustering around the charging ion, and the molecules of interest is a key parameter.

The humidity has to be carefully considered, particularly when developing a new application or experimental set-up because:

• Exhaled air from the alveolar region of the lungs has a very steady humidity level, with a dew point regulated by the body temperature (36-37ºC). For breath research and analysis, the humidity is self-regulated.
  

• In headspace analysis (or the analysis of other humid samples), controlling the temperature and the humidity of the sample is crucial to ensure a constant humidity level. Adding extra humidity helps to boost some signals and to eliminate possible variations.

Better understanding the SESI ionization mechanism in different conditions is key to improve linearity. Humidity plays a very important role in the ionization, but quantification is still. Our R&D team is working on numerical models to understand this role and better to ensure that no variations in the humidity level will affect the ionization efficiency and thus the measurements.

We have worked in SESI-MS for 10 years now, if you would like to know more about how our core solution SUPER SESI works, contact us to ask any questions or keep on reading here.