Topic Single-Particle Mass Spectrometry

Dr. Johannes Passig

Overview

Fig. 1: (top) Spatio-temporal matching of the laser excitation to the evolving particle (plasma) plume allow for the simultaneous detection of toxic aromatic hydrocarbons and the inorganic composition of individual particles [2]. (bottom) Model of the optical detection and sizing unit.

Atmospheric aerosols play a key role in the earth climate and biogeochemical cycles. Moreover, the global deaths caused by exposure to ambient particulate matter with a diameter less than 2.5 µm (PM2.5) reached 4.2 million in 2015 and is further increasing with the rapid development of mobile industrial societies. However, the observation of toxic trace compounds, their distribution, transport pathways, and degradation are so-far limited by technological challenges. Single-particle mass spectrometry (SPMS) can tackle many of these issues by obtaining the size and a chemical profile from individual particles in real time. However, the conventional laser ionization method in SPMS leads to strong fragmentation of important species, impeding their identification and provides only limited data on the particle composition.

 

Our research focuses on new technologies that acquire chemical information from individual, microscopic particles. Key is the understanding and optimization of complex laser-matter interactions for efficient and non-destructive ablation, ionization and detection of health-relevant trace components from particles. We exploit resonances between laser radiation and molecules or atoms to detect such species with masses in the order of 10-16–10-12 g per particle.

Basic working principle

In single-particle mass spectrometry (SPMS) [6,7], airborne particles are accelerated in a gas expansion into vacuum. Their size is determined by their final velocity, measured by Mie scattering in a pair of laser beams (laser velocimetry). An electronic circuit calculates the arrival time of each individual particle in the ion source of the mass spectrometer and triggers the desorption- and ionization laser pulses that hit the particles ‘on-the-fly’ for the desired excitation and ionization scheme. The resulting ions are analyzed in a bipolar mass spectrometer, detecting positive and negative ions in opposite time-of-flight mass analyzers. Fast digitizes record the mass spectra of every individual particle and pattern recognition algorithms based on artificial neural networks classify the particles for source apportionment.

Field studies

An important example are polycyclic aromatic hydrocarbons (PAHs), toxic organic trace compounds originating from natural and anthropogenic combustion, e.g. from coal, vehicles or wildfires. Bound on airborne particles, they are transported over long distances. Their distribution is a crucial factor for health effects from air pollution. On one hand, PAHs can by equally distributed with low concentration over the particle ensemble, thus being metabolized after inhalation. On the other hand, they might be present on few particles with high concentration, overcoming the lung’s cellular defense and leading to local inflammation – a starting point for serious health effects that are associated with asthma, cardiovascular diseases or cancer. We developed mass spectrometers that detect less than 10-15 g of PAHs on individual particles and obtain additional information on the particle’s origin and atmospheric transport [2].

Fig. 2: The laser-controlled mixing of resonant- and non-resonant ionization mechanisms reveals the key particle components for health effects. (top) Heavy-metal containing particle from coal combustion after long-range atmospheric transport from Eastern Europe to Rostock. (bottom) Particle of 400 nm size containing PAHs from wood combustion. The sulfate- and oxalate signals left indicate oxidation by photochemistry and atmospheric transport [2].

Another research focus are particle-bound metals that affect ecosystems and human health. Inhaled transition metals such as iron (Fe) induce oxidative stress and are involved in health effects from air pollution [3]. Furthermore, metal-containing aerosols are important sources of marine micronutrients affecting primary production and carbon fixation in the world's oceans [4]. We tune laser pulses to atomic resonances of metals, enhancing the sensitivity of SPMS for these biologically relevant aerosol components. Thus, we help to elucidate the sources and transport pathways of bioavailable metals to the oceans [5].

Fig. 3: Principal component analysis of single-particle chemical profiles from background aerosol measured at two days in autumn at the Swedish coast. The particles were classified from SPMS data using a neural network algorithm (ART-2a). Exploiting laser-atom resonances, our new ionization approach reveals that organic aerosols from industrial/traffic combustion dominate the transport of biologically relevant iron (circulated) – affecting marine communities and human health. However, also mixtures with sea salt contribute to Fe transport. For details see [5].

Beyond air pollution, we are also interested in the detection of safety-relevant substances, e.g. dusts of explosives or dangerous drugs. Therefore, we optimize SPMS for their real-time detection, using safe model substances such as ibuprofen powder as shown in the mass spectra below.

Fig. 4: The technology is also applicable to powders of non-volatile molecular species and medical preparations, as indicated by the mass spectra of single particles from aspirin and ibuprofen powder.

Contact

University of Rostock
Institute of Chemistry
Division of Analytical and Technical Chemistry

Dr. Johannes Passig

Dr.-Lorenz-Weg 2 &
Albert Einstein Straße 25
18059 Rostock
Germany

Tel: +49 (0) 381 498 - 8989
johannes.passiguni-rostockde

 

University of Rostock
Institute of Chemistry
Division of Analytical and Technical Chemistry
Department Life Light & Matter

Dr. Julian Schade

Albert-Einstein-Straße 25
18059 Rostock (Germany)

Tel.: +49 (0) 381 498 - 8978
julian.schadeuni-rostockde

References

References

[1] WHO, Ambient Air Pollution: A global assessment of exposure and burden of disease, report, (2016)

[2] J. Schade, J. Passig, R.Irsig, S. Ehlert, M. Sklorz, T. Adam, C. Li, Y. Rudich, R. Zimmermann, Spatially Shaped Laser Pulses for the Simultaneous Detection of Polycyclic Aromatic Hydrocarbons as well as Positive and Negative Inorganic Ions in Single Particle Mass Spectrometry, Anal. Chem. 91, 15, 10282-10288, (2019)

[3] Ye, D., Klein, M., Mulholland, J. A., Russell, A. G., Weber, R., Edgerton, E. S., Chang, H. H., Sarnat, J. A., Tolbert, P. E., and Ebelt Sarnat, S.: Estimating Acute Cardiovascular Effects of Ambient PM2.5 Metals, Environ. Health Persp. 126, 27007, (2018)  

[4] N. M. Mahowald, D. S. Hamilton, K. R. M. Mackey, J. K. Moore, A. R. Baker, R. A. Scanza, Y. Zhang, Aerosol trace metal leaching and impacts on marine microorganisms, Nat. Commun. 9, 2614 (2018)

[5] J. Passig, J. Schade, E.-I. Rosewig, R. Irsig, T. Kröger-Badge, H. Czech, M. Sklorz, T. Streibel, L. Li, X. Li, Z. Zhou, H. Fallgren, J. Moldanova, R. Zimmermann, Resonance-enhanced detection of metals in aerosols using single-particle mass spectrometry, Atmos. Chem. Phys. 20, 7139–7152, (2020)

[6] K. Pratt, K. Prather, Mass spectrometry of atmospheric aerosols-Recent developments and applications. Part II: On-line mass spectrometry techniques, Mass Spectrom. Rev., 31: 17-48, (2012)

[7] J. Passig, R. Zimmermann, Laser Ionization in Single‐Particle Mass Spectrometry, book chapter in Photoionization and Photo‐Induced Processes in Mass Spectrometry: Fundamentals and Applications, Wiley-VCH, ISBN: 9783527335107, (2021)