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New method for the precise analysis of the composition of secondary organic aerosols in PM

Researchers in Poland have developed a new precise method for the chemical analysis of secondary organic aerosol (SOA)—an important yet not fully characterized constituent of atmospheric particulate matter. The method, easily adaptable in many modern laboratories, not only determines the chemical composition of compounds, but also recognizes changes in the spatial distribution of atoms in molecules.

The Warsaw-based scientists from the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS), the Institute of Organic Chemistry of the PAS and the Institute of Environmental Protection of the National Research Institute presented their method in a paper in the ACS journal Analytical Chemistry.

The chemical properties of molecules, especially organic ones, are determined not only by their chemical composition itself, but also by the spatial structure of the molecules. SOAs are characterized by a richness of chemical compounds, many of them occurring in isomeric forms—i.e., differing in the distribution of atoms in the molecule, and consequently also in their chemical properties. The detection of these isomers used to be the weak point of modern analytical techniques.

Atmospheric aerosols are a major pollutant of the Earth’s atmosphere. They consist of fine particulate matter with diameters below 100 μm that are suspended in the air. A large proportion of aerosols originate in the atmosphere through the chemical transformation of volatile organic compounds (VOCs) followed by gas-to-particle partitioning and/or transfer, followed by further reaction therein. These aerosols are known as secondary organic aerosols (SOA). Consequently, SOA particles are complex mixtures of organic and inorganic compounds that have a negative impact on human health, influence the biosphere and take part in climate change.

The organic fraction of atmospheric aerosols is one of the most important subjects of recent atmospheric studies. … Most of these compounds are strongly hydrophilic and occur as minute quantities in samples. Thus, they are difficult to separate or analyze with conventional techniques and resist detailed identification of molecular structure, including differentiation of positional and/or stereo isomers. … the quantification of SOA components of complex isomeric profiles remains a challenge for analytical atmospheric chemists.

The goal of this study was to optimise and improve commonly used UHPLC [ultra-high performance liquid chromatography] methods and create a tool for the qualitative comparison for SOA compositions obtained in different environmental laboratories.

—Spolnik et al.

The Warsaw-based scientists have shown that a very accurate chemical composition of the atmospheric aerosol can be obtained without any great financial expenditure, with the help of apparatus already operating in many contemporary laboratories. There is only one condition: during the analysis, various analytical chemistry tools need to be skillfully combined. In this tandem analytical technique, the key role is played by the specific combination of possibilities offered by two quite common analytical techniques: chromatography and mass spectrometry.

Particulate matter is collected for research using special samplers. They suck in air, which passes through a system of nozzles allowing for division of the aerosol particle fractions depending on their size. What enters the instrument reaches a clean quartz fibre disc on which it is deposited. Then, by means of solvent extraction, the collected aerosol particles are transferred to the solution and concentrated there. As part of our method, we chose, among others, more effective solvents for transferring particles to the solution, which significantly improved the results obtained by mass spectrometry.

—Dr. Rafal Szmigielski, corresponding author and professor at IPC PAS

The new method of analyzing smog particles is accurate and fully reproducible. Samples taken from the same place, analyzed in different laboratories, lead to the same results. This means that those who are professionally responsible for monitoring the environment will be able to provide the public with truly reliable information on the current concentration of pollutants in the air.

Knowledge of not only the chemical composition of smog particles, but also the isomers of its individual components, is of additional, significant practical significance. With such accurate knowledge, scientists are able to more precisely identify the sources responsible for the emission of individual compounds and recreate the migration of pollutants in the atmosphere.

Resources

  • Grzegorz Spolnik, Paulina Wach, Krzysztof J. Rudzinski, Krzysztof Skotak, Witold Danikiewicz, and Rafal Szmigielski (2018) “Improved UHPLC-MS/MS Methods for Analysis of Isoprene-Derived Organosulfates” Analytical Chemistry 90 (5), 3416-3423 doi: 10.1021/acs.analchem.7b05060

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