Real-time Partitioning of Organic Acids Using an Ambient Ion Monitor: Opportunities and Challenges Presented by Addition of a Mass Spectrometer

TREVOR VANDENBOER, Mayré Rodriguez Ramirez, Eric Vanhauwaert, Jessica Clouthier, Shira Joudan, Cora Young, York University

     Abstract Number: 447
     Working Group: Exhibitor and Instrument Application Showcase

Abstract
Organic acids in the atmosphere are formed after the oxidation of volatile organic and chemical compounds; the most abundant organic acid is formic acid. Trifluoroacetic acid (TFA) is a fluorinated organic acid that has been found in the atmosphere; it is a persistent compound and is resistant to environmental degradation.

A few techniques have been developed to measure organic acids in the gas and particle phase, restricted to offline, highly time-integrated, and subject to sampling biased methods. We developed a new technique to simultaneously measure trace levels of organic acids in the gas and particle phase (<2.5 µm) in real-time using an ambient ion monitor (AIM) coupled to an ion chromatograph (IC) and a mass spectrometer (MS), that with the use of different internal standards (IS), quantifies lower atmospheric amounts with greater accuracy.

The AIM-IC-MS is a world-unique online instrument that samples air hourly, an IC with anion and cation columns and conductivity detectors, and a single quadrupole mass spectrometer (MS) as a second detector for anions to separate and measure the conjugated base of water-soluble organic acids that cannot typically be resolved in under 30 minutes. Typical major ions in ambient air vary in abundance and cause co-elution and ion suppression in the MS. For this reason, bromide, 13C2 TFA, and acetic acid-d3 are added as IS in both gas and particle samples.

The AIM-IC-MS was used during the Toronto Halogens, Emissions, Contaminants, and Inorganics eXperiment (THE CIX) campaign in Toronto during July and August 2023. We will show how the system expands the suite of quantifiable analytes and use of IS impacts the accuracy of the measurements, focusing on TFA and formic acid. How to properly select the correct IS for each desired analyte will be discussed.