Improving the Quantification of Secondary Organic Aerosol Using a Microflow Reactor Coupled to HPLC-MS and NMR to Manufacture Ad Hoc Calibration Standards

An Automated Methodology for Non-targeted Compositional Analysis of Small Molecules in High Complexity Environmental Matrices Using Coupled Ultra Performance Liquid Chromatography Orbitrap Mass Spectrometry

The life-critical matrices of air and water are among the most complex chemical mixtures that are ever encountered. Ultrahigh-resolution mass spectrometers, such as the Orbitrap, provide unprecedented analytical capabilities to probe the molecular composition of such matrices, but the extraction of non-targeted chemical information is impractical to perform via manual data processing. Automated non-targeted tools rapidly extract the chemical information of all detected compounds within a sample dataset. However, these methods have not been exploited in the environmental sciences. Here, we provide an automated and (for the first time) rigorously tested methodology for the non-targeted compositional analysis of environmental matrices using coupled liquid chromatography-mass spectrometric data. First, the robustness and reproducibility was tested using authentic standards, evaluating performance as a function of concentration, ionization potential, and sample complexity. The method was then used for the compositional analysis of particulate matter and surface waters collected from worldwide locations. The method detected >9600 compounds in the individual environmental samples, arising from critical pollutant sources, including carcinogenic industrial chemicals, pesticides, and pharmaceuticals among others. This methodology offers considerable advances in the environmental sciences, providing a more complete assessment of sample compositions while significantly increasing throughput.

Multidimensional Analytical Characterization of Water-Soluble Organic Aerosols: Challenges and New Perspectives

Water-soluble organic aerosols (OA) are an important component of air particles and one of the key drivers that impact both climate and human health. Understanding the processes involving water-soluble OA depends on how well the chemical composition of this aerosol component is decoded. Yet, obtaining detailed information faces several challenges, including water-soluble OA collection, extraction, and chemical complexity. This review highlights the multidimensional non-targeted analytical strategies that have been developed and employed for providing new insights into the structural and molecular features of water-soluble organic components present in air particles. First, the most prominent high-resolution mass spectrometric methods for near real-time measurements of water-soluble OA and their limitations are discussed. Afterward, a special emphasis is given to the degree of compositional information provided by offline multidimensional analytical techniques, namely excitation–emission (EEM) fluorescence spectroscopy, high-resolution mass spectrometry and two-dimensional nuclear magnetic resonance (NMR) spectroscopy and their hyphenation with chromatographic systems. The major challenges ahead on the application of these multidimensional analytical strategies for OA research are also addressed so that they can be used advantageously in future studies.

Infrared Ion Spectroscopy of Environmental Organic Mixtures: Probing the Composition of α-Pinene Secondary Organic Aerosol

Characterizing the chemical composition of organic aerosols can elucidate aging mechanisms as well as the chemical and physical properties of the aerosol. However, the high chemical complexity and often low atmospheric abundance present a difficult analytical challenge. Milligrams or more of material may be needed for speciated spectroscopic analysis. In contrast, mass spectrometry provides a very sensitive platform but limited structural information. Here, we combine the strengths of mass spectrometry and infrared (IR) action spectroscopy to generate characteristic IR spectra of individual, mass-isolated ion populations. Soft ionization combined with in situ infrared ion spectroscopy, using the tunable free-electron laser FELIX, provides detailed information on molecular structures and functional groups. We apply this technique, along with quantum mechanical modeling, to characterize organic molecules in secondary organic aerosol (SOA) formed from the ozonolysis of α-pinene. Spectral overlap with a standard is used to identify cis-pinonic acid. We also demonstrate the characterization of isomers for multiple SOA products using both quantum mechanical computations and analyses of fragment ion spectra. These results demonstrate the detailed structural information on isolated ions obtained by combining mass spectrometry with fingerprint IR spectroscopy.