Characterization of Organic Compounds in Atmospheric Nanoparticles by Thermal Extraction - Comprehensive Two-Dimensional Gas Chromatography (GC x GC) in Combination with Selective Detection, Mass Spectrometry and Accurate Mass Detection

Significance of the Topic

Understanding organic composition of atmospheric nanoparticles is critical due to their health impacts and role in air pollution The small size high surface area and complex chemistry of nanoparticles pose challenges for sample collection and analysis

Objectives and Study Overview

This study presents a workflow combining thermal extraction comprehensive two dimension gas chromatography GC x GC high resolution time of flight mass spectrometry HRTOF MS and simultaneous selective detection to characterize organic compounds in roadside nanoparticles of 29 58 nm diameter The goals include tentative identification of trace level organics including heteroatomic species and quantitative profiling of polycyclic aromatic hydrocarbons PAHs across size resolved fractions

Methodology and Used Instrumentation

Sampling was performed in a high traffic roadside monitoring site in Kawasaki Japan with a low pressure impactor collecting 13 aerodynamic size fractions Thermal extraction was carried out with a GERSTEL TDS 2 thermal desorber Cryo focusing in a programmable temperature vaporization inlet preceded GC x GC separation on a non polar BPX 5 first column and a polar BPX 50 second column with a Zoex loop modulator Detection was achieved by a high resolution TOF MS operated at 25 Hz for accurate mass measurement and by simultaneous nitrogen phosphorus detection NPD coupled to a rapid scanning quadrupole MS for selective identification of nitrogen containing compounds Quantitative analysis used the qMS with limited mass range and high scan rate for improved data density

Main Results and Discussion

• Over one thousand peaks detected in the 29 58 nm fraction spanning alkanes alkenes fatty acids ketones substituted aromatics PAHs oxy PAHs and heterocyclic species
• Exact mass extraction with a 0.05 Da window coupled to NIST library matching yielded tentative identification of 50 compounds with average mass error of 0.91 mDa and 27 compounds below 2 mDa error
• Group type separation of oxy PAHs was enhanced using narrow extracted ion slices in two dimension space enabling clear visualization and structural assignment
• Simultaneous NPD and qMS detection confirmed 15 nitrogen containing compounds by direct matching of retention times in both detectors
• Method validation for 12 PAHs demonstrated linearity of r2 greater than 0.98 limits of quantification below 11 pg and retention time repeatability under 1 percent with response repeatability under 9 percent
• Size dependent PAH load normalized by PM mass peaked in the smallest fraction reaching up to 39 pg per microgram of PM

Benefits and Practical Applications

• Enables comprehensive speciation of complex organic mixtures in ultralow mass samples
• Combines high resolution mass accuracy and group type separation for confident assignment of trace constituents
• Simultaneous selective and mass detection accelerates targeted identification of heteroatom containing analytes
• Quantitative size resolved PAH profiles support source apportionment and health impact assessments

Future Trends and Potential Applications

The integration of faster exact mass detectors with selective detectors and advanced data mining algorithms will further enhance sensitivity dynamic range and confidence in compound identification Automated workflows may enable routine monitoring of urban industrial and indoor aerosols and extend to biomonitoring of inhaled particulate matter

Conclusion

A novel thermal extraction GC x GC method combining HRTOF MS and simultaneous selective detection was demonstrated for in depth qualitative and quantitative analysis of organic compounds in sub 100 nm atmospheric particles The approach delivers comprehensive coverage of trace components and valuable insight for aerosol research and air quality monitoring

Reference

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