Environmental Air Monitoring by TD/GC-TOF MS with Variable-energy Ionisation

Oral Presentation

Prepared by N. Watson1, P. Grosshans1, L. McGregor2
1 - Markes International, 11126-D Kenwood Road, Suite D, Cincinnati, OH, 45242, United States
2 - Markes International, Gwaun Elai Mediscience Campus, Llantrisant, RCT, CF72 8XL, United Kingdom

Contact Information: nwatson@markes.com; 866-483-5684


Gas chromatography with time-of-flight mass spectrometry (GC-TOF MS) offers highly sensitive detection and confident mass spectral identification of trace-level analytes. The combination of this technique with thermal desorption (TD) for the collection and pre-concentration of volatile and semi-volatile organic compounds makes it the ideal choice for monitoring air quality. The nature of TOF allows fast GC of complex samples, which not only saves time but also compresses the chromatography, further improving signal-to-noise values. Nevertheless, the identification of individual compounds may be hindered by weak molecular ions or when similar mass spectral characteristics are evident across entire chemical classes.

Select-eV ion source technology aims to solve this problem through the ability to switch between hard and soft electron ionisation with no inherent loss in sensitivity. The enhancement in absolute intensity of molecular ions at low ionisation energy extends the limits of detection. Additionally, Select-eV provides reduced fragmentation whilst retaining structurally-significant fragments, thus minimising spectral noise and further improving both the sensitivity and selectivity. Select-eV can therefore offer more robust quantification of target compounds, even within complex matrices.

Moreover, background gases (e.g. carrier gas, CO2, etc.) are not ionised at low ionisation energy, further increasing the selectivity of the technique. This is particularly useful for the detection and identification of low molecular weight compounds, such as 2-propanol and ethanol, which use m/z 45 for quantification in environmental air samples. The carbon dioxide 13C isotope also has m/z of 45, which can cause interference when quantifying these compounds at low concentrations.

This work demonstrates the increased dimensionality afforded by TD/GC-TOF MS with variable-energy ionisation for enhanced confidence in the identification and quantitation of VOCs in air.