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

Abstract

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.

UV/Vis and IRMPD Spectroscopic Analysis of the Absorption Properties of Methylglyoxal Brown Carbon

“…This technique has been used to probe the ground-state conformation of different systems including biomolecules 43−48 and recently in monomers formed in α-pinene SOA. 33 For the current study, IRMPD spectroscopy was used to investigate the low-energy conformations of protonated and neutral IC. Protonated IC is observed in the positive ion mode as an ion with m/z 125.…”

“…Infrared action spectra of mass-to-charge selected ions were collected at the FELIX laboratory following a similar methodology to our previous work. 33 Briefly, positive-ion electrospray ionization was run on a Bruker Amazon ion trap mass spectrometer that is coupled to the infrared laser beam line. 34 Here, 10 μL of the concentrated MG BrC stock was diluted with 10 mL of methanol to produce the sample solution.…”

Metabolite Identification Using Infrared Ion Spectroscopy─Novel Biomarkers for Pyridoxine-Dependent Epilepsy

“…Very recently, several groups have suggested infrared ion spectroscopy (IRIS) as an alternative mass spectrometry-based technique for small-molecule identification. − By combining the sensitivity and mass selectivity of MS­(/MS) with infrared spectroscopy-based orthogonal structural characterization, IRIS is able to provide detailed structural information to annotate detected features arising from MS analyses. IRIS can provide a mass-selective fingerprint IR spectrum for essentially any ion detected in an MS experiment.…”

Evaluation of table-top lasers for routine infrared ion spectroscopy in the analytical laboratory

“…Consequently, IRIS has found recent application in a range of biochemical areas such as drug metabolism, 26,27 clinical chemistry, 28–30 forensics 31–34 and environmental sciences. 35,36 …”