Nontarget Tandem High-Resolution Mass Spectrometry Analysis of Functionalized Organic Compounds in Atmospherically Relevant Samples

Abstract

We present a data analysis workflow for nontarget tandem high-resolution mass spectrometry (MS), with the aim being full speciation of functionalized organic compounds in complex atmospheric samples without unambiguous molecular structure assignment. The workflow was demonstrated for four types of samples, including primary-emission aerosols, secondary organic aerosols, ambient aerosols, and rainwater, but could be applicable to other environmental samples. With a single mass spectrometry run, the combined MS1 and MS2 analysis provided molecular formula, functional group, and aromaticity information for 68.1–88.8% of deprotonated molecules and 58.6–84.7% of protonated molecules. We determined relative abundances of 22 and 21 compound categories for deprotonated and protonated molecules, respectively, on the basis of the assignment of a variety of oxygen-, nitrogen-, and sulfur-containing functional groups. Molar concentrations of compound categories were further semiquantified with surrogate standards in electrospray ionization negative mode, ranging from 10–4 to 1 nmol (μg of source aerosol mass)−1, from 3 × 10–3 to 2 nmol m–3 in the atmosphere, and from 2 × 10–3 to 1 nmol (mL of rainwater)−1. The assignment and quantification of functional groups provided new chemical fingerprints of organic compounds to trace their sources, formation, and aging in the atmosphere and also allowed the use of group contribution methods to study the physicochemical properties of organic aerosols.