Analysis of Airborne Carboxylic Acids and Phenols as Their Pentafluorobenzyl Derivatives: Gas Chromatography/Ion Trap Mass Spectrometry with a Novel Chemical Ionization Reagent, PFBOH

Abstract

The complex photochemical transformations of biogenic hydrocarbons such as isoprene and of anthropogenic hydrocarbons such as aromatics are an important source of carboxylic acids in the troposphere. The identification of unknown carboxylic acids can be difficult, however, due to the lack of standards as well as poor sensitivity and lack of selectivity of existing techniques. In this study, we describe the development of a method to analyze airborne carboxylic acids using derivatization with pentafluorobenzyl bromide (PFBBr) followed by capillary gas chromatography/ion trap mass spectrometry (GC/ITMS) analysis. In addition to the typical electron impact ionization (EI) and methane chemical ionization (CI) mass spectra of pentafluorobenzyl derivatives, we describe the use of pentafluorobenzyl alcohol (PFBOH) as a novel reagent gas for CIMS. Pentafluorobenzyl ions (m/z = 181) were produced at reduced pressure (1 × 10-5−2 × 10-5 Torr) from PFBOH gas, and the resulting CIMS were characterized by the predominance of the [M + 181]+ ions. The carboxylic acid products in the oxidation of isoprene from indoor and outdoor smog chamber experiments were analyzed using the described PFBBr GC/ITMS method. The formation of methacrylic acid in an isoprene/O3 reaction was demonstrated experimentally for the first time, and acrylic acid, one of the U.S. EPA 189 Hazardous Air Pollutants, is first reported here as an isoprene oxidation product. In other outdoor toluene/NOx chamber experiments, we detected a series of carboxylic acids and various phenolic compounds using this method.