Comparison Between Mass Spectra of Individual Organic Particles Generated by UV Laser Ablation and in the IR/UV Two-Step Mode
One of the most fundamental aspects of single particle mass spectrometry is that the individual particle mass spectra are first classified and only then averaged. When ions are generated by ablation with a UV laser the mass spectra of particles with identical compositions exhibit large particle to particle fluctuations in the mass spectral intensity pattern. This is particularly true when it comes to particles containing organic molecules. At laser fluence that is sufficient to ionize sulfates many of the organic molecules exhibit high degree of fragmentation, often to the point where they cannot be distinguished from elemental carbon. In contrast, when ion generation is separated into two steps, in which the first step uses infra red to evaporate the semi-volatile components and the second, time delayed UV pulse to ionize the evaporating plume, the quality of the individual particle mass spectra are significantly improved. We present an experimental investigation of the properties and behavior of individual particle mass spectra of organic particles that are generated by ablation and in two steps. We investigate the effect of UV laser fluence and the delay between the two lasers. The study shows that the two step approach yields highly reproducible mass spectra that contain sufficient detail to allow clear molecular assignments. The two step approach also produces 10 times as many ions, and the mass spectral intensity can be related to the amount of organics in the particle. In contrast, ablation generated mass spectra were found to exhibit high degree of fragmentation and particle-to-particle fluctuations.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 958491
- Report Number(s):
- PNNL-SA-62555; 24590; KC0302020; TRN: US201002%%58
- Journal Information:
- International Journal of Mass Spectrometry, 282(1-2):6-12, Vol. 282, Issue 1-2
- Country of Publication:
- United States
- Language:
- English
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