Researchers from several leading Warsaw scientific institutions have collaborated to develop a new, extremely precise method for the chemical analysis of suspended particulate matter comprising smog. The method, easily adaptable in modern laboratories, not only determines the chemical composition of compounds, but even recognizes changes in the spatial distribution of atoms in molecules.
Atmospheric particulate matter, popularly known as smog, is becoming increasingly troublesome. Smog attacks the lungs of the inhabitants of big cities, and in industrialized countries, it is literally everywhere, even in forest areas seemingly distant from urban agglomerations. Smog is characterized by a huge richness of chemical compounds, many of them occurring in isomeric forms, 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—until now.
In the pages of Analytical Chemistry, 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 present a method of extremely precise analysis of smog particles. The new analytical technique can be used by any relatively modernly equipped chemical laboratory.
"What is really reaching our lungs? When we look closely at air samples, it turns out that they contain a lot of aerosols. In most cases, these particles, with sizes in the order of micro- or even nanometers, are of natural origin. These are mainly particles produced in gigantic quantities by complex atmospheric processes, whose main drivers are plants, especially forests," says Dr. Rafal Szmigielski, professor at the IPC PAS, head of the research team which has for years been dealing with atmospheric chemistry, including the mechanisms of suspended particulate matter formation and the evolution of smog.
The combustion of various substances—including in household furnaces, car engines and industrial facilities—introduces into the atmosphere a whole range of chemical compounds. Anthropogenic pollution, including nitrogen oxides, is not only in itself detrimental to health, its impact is heightened by the fact that it modifies the composition of the natural atmosphere, leading to its permanent contamination. Today, the correlation between long-term exposure to smog and the incidence of heart or lung disease is very clear.
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. "A single chemical compound, detected in an aerosol by existing methods, may actually be a whole group of stereoisomers. They will all have the same chemical composition, but due to the different distribution of atoms in the molecule, they can have completely different affinities, for example, to proteins or cell receptors. Functionally, then, they will be different substances with different effects on our health. This entire isomeric zoo has so far eluded the eyes of chemists," explains Prof. Szmigielski.
The Warsaw-based scientists have shown that a very accurate chemical composition of atmospheric aerosols can be obtained without any great financial expenditure, using equipment already operating in many contemporary laboratories. During the analysis, various analytical chemistry tools are combined. In this tandem analytical technique, the key role is played by the specific combination of 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," explains Prof. Szmigielski.
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 researchers will be able to provide the public with truly reliable information on the current concentration of pollutants in the air.
Knowledge of the chemical composition of smog particles and the isomers of its individual components is of 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.
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Grzegorz Spolnik et al, Improved UHPLC-MS/MS Methods for Analysis of Isoprene-Derived Organosulfates, Analytical Chemistry (2018). DOI: 10.1021/acs.analchem.7b05060