An atmospheric pressure field effect ionisation source for ion mobility spectrometry

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Ion Mobility Spectrometry

Background:

• Atmospheric pressure ionisation sources are crucial for analytical techniques like ion mobility spectrometry (IMS).
• Existing sources, such as atmospheric pressure corona discharge (APCD), have limitations.
• Developing novel, reliable ionisation sources is essential for advancing IMS capabilities.

Purpose of the Study:

• To develop and characterize a novel atmospheric pressure field effect (APFE) ionisation source for drift tube ion mobility spectrometry.
• To evaluate the performance of the APFE source in both positive and negative polarities.
• To compare the APFE source with the atmospheric pressure corona discharge (APCD) ionisation source.

Main Methods:

• Development of an APFE ionisation source with a point-to-plane geometry, featuring a 10 μm Pt electrode and 20 GΩ current limiters.
• Investigation of negative and positive ion formation in synthetic air using the APFE source.
• Utilisation of an Ion Mobility Spectrometer coupled with an orthogonal acceleration Time of Flight Mass Spectrometer (IMS-oa-TOF-MS) for ion identification.
• Demonstration of chemical ionisation for specific molecules in both polarities.

Main Results:

• The APFE source successfully generated key reactant ions (RIs) in both polarities: O₂⁻(H₂O) and O₂⁻CO₂(H₂O) in negative mode, and H⁺(H₂O) in positive mode.
• Stable production of RIs was achieved across different gas flow regimes within the IMS.
• The APFE source proved to be a reliable chemical ionisation source at atmospheric pressure.
• Successful chemical ionisation of 2,6-di-tert-butyl-pyridine (positive polarity) and tetrachloromethane (negative polarity) was demonstrated.

Conclusions:

• The developed APFE ionisation source is a robust and versatile tool for drift tube ion mobility spectrometry.
• The APFE source offers a reliable alternative for atmospheric pressure chemical ionisation, comparable to or exceeding APCD performance.
• This advancement facilitates broader applications of IMS in chemical analysis.