Study of the Chemical Ionization of Organophosphate Esters in Air Using Selected Ion Flow Tube–Mass Spectrometry for Direct Analysis

Abstract

Organophosphate esters are an emerging environmental concern since they spread persistently across all environmental compartments (air, soil, water, etc.). Measurements of semivolatile organic compounds are important but not without challenges due to their physicochemical properties. Selected ion flow tube-mass spectrometry (SIFT-MS) can be relevant for their analysis in air because it is a direct analytical method without separation that requires little preparation and no external calibration. SIFT-MS is based on the chemical reactivity of analytes with reactant ions. For volatile and semivolatile organic compound analysis in the gas phase, knowledge of ion–molecule reactions and kinetic parameters is essential for the utilization of this technology. In the present work, we focused on organophosphate esters, semivolatile compounds that are now ubiquitous in the environment. The ion–molecule reactions of eight precursor ions that are available in SIFT-MS (H3O+, NO+, O2 •+, OH–, O•–, O2 •–, NO2 –, and NO3 –) with six organophosphate esters were investigated. The modeling of ion–molecule reaction pathways by calculations supported and complemented the experimental work. Organophosphate esters reacted with six of the eight precursor ions with characteristic reaction mechanisms, such as protonation with hydronium precursor ions and association with NO+ ions, while nucleophilic substitution occurred with OH–, O•–, and O2 •–. No reaction was observed with NO2 – and NO3 – ions. This work shows that the direct analysis of semivolatile organic compounds is feasible using SIFT-MS with both positive and negative ionization modes.

A SIFT-MS study of positive and negative ion chemistry of theortho-,meta- andpara-isomers of cymene, cresol, and ethylphenol

“…Aromatic compounds are an essential chemical class which are analysed in gas-phase complex matrices including human breath; 1–3 headspace of samples such as cosmetics 4 and food stuffs; 5 ambient air for air quality analysis for environmental monitoring purposes; 6–9 as well as investigating ion–molecule reactions, at the centre of the SIFT-MS technique. In particular, aromatic compounds are often of great interest in the field of atmospheric chemistry and air pollution research as many of these species are known to be highly toxic and are released from anthropogenic emissions into the atmosphere, diminishing air quality.…”

“…Whilst analyses of mixtures of multiple analytes are possible, it is currently not easy to analyse isomeric or isobaric species present simultaneously within a matrix. However, as the range of reagent ions available to SIFT-MS has been recently expanded to include anions (H 3 O + , NO + , O 2 + , O À , OH À , O 2 À , NO 2 À , NO 3 À ), there is potential to use differing ionic products, produced from the range of reactions to facilitate simultaneous quantification, of isobaric species using SIFT-MS. Aromatic compounds are an essential chemical class which are analysed in gas-phase complex matrices including human breath; [1][2][3] headspace of samples such as cosmetics 4 and food stuffs; 5 ambient air for air quality analysis for environmental monitoring purposes; [6][7][8][9] as well as investigating ion-molecule reactions, at the centre of the SIFT-MS technique. In particular, aromatic compounds are often of great interest in the field of atmospheric chemistry and air pollution research as many of these species are known to be highly toxic and are released from anthropogenic emissions into the atmosphere, diminishing air quality.…”

How to Use Ion-Molecule Reaction Data Previously Obtained in Helium at 300 K in the New Generation of Selected Ion Flow Tube Mass Spectrometry Instruments Operating in Nitrogen at 393 K

“…Selected ion flow tube-mass spectrometry (SIFT-MS) is a soft chemical ionization technique increasingly used globally to directly analyze volatile organic compounds (VOCs) within gaseous media. , SIFT-MS has become a particularly popular technique in the analysis of human breath in clinical settings; , the monitoring of the environment (i.e., atmospheric chemistry); − headspace analysis of samples (such as foods and cosmetics); , the analysis of contaminants within hydrogen (as a fuel); as well as airborne molecular contaminants in semiconductor manufacturing . A common theme in this diverse scope of applications of SIFT-MS is the attempt at immediate and absolute quantification of targeted VOCs.…”