Effects of modular ion-funnel technology onto analysis of breath VOCs by means of real-time mass spectrometry

Giovanni Pugliese,Jochen K Schubert,Phillip Trefz,Wolfram Miekisch,Felix Piel,Philipp Sulzer

doi:10.1007/s00216-020-02846-8

Abstract

Proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) is a powerful tool for real-time monitoring of trace concentrations of volatile organic compounds (VOCs). The sensitivity of PTR-ToF-MS also depends on the ability to effectively focus and transmit ions from the relatively high-pressure drift tube (DT) to the low-pressure mass analyzer. In the present study, a modular ion-funnel (IF) is placed adjacent to the DT of a PTR-ToF-MS instrument to improve the ion-focusing. IF consists of a series of electrodes with gradually decreasing orifice diameters. Radio frequency (RF) voltage and direct current (DC) electric field are then applied to the electrodes to get the ions focused. We investigated the effect of the RF voltage and DC field on the sensitivity of a pattern of VOCs including hydrocarbons, alcohols, aldehydes, ketones, and aromatic compounds. In a proof-of-concept study, the instrument operating both as normal DT (DC-mode) and at optimal IF conditions (RF-mode) was applied for the breath analysis of 21 healthy human subjects. For the range of investigated VOCs, an improvement of one order of magnitude in sensitivity was observed in RF-mode compared with DC-mode. Limits of detection could be improved by a factor of 2–4 in RF-mode compared with DC-mode. Operating the instrument in RF-mode allowed the detection of more compounds in the exhaled air compared with DC-mode. Incorporation of the IF considerably improved the performance of PTR-ToF-MS allowing the real-time monitoring of a larger number of potential breath biomarkers.Graphical abstract

Highlights

Proton transfer reaction mass spectrometry (PTR-MS) is an analytical technique that allows real-time monitoring of volatile organic compounds (VOCs) at low concentrations
H3O+ intensity showed its maximum value at radio frequency (RF) = 80 V peak-to-peak (Vp-p) under dry conditions (Fig. 2 (a)) and at RF = 120 V under humid conditions (Fig. 2 (b))
An increase of the water cluster intensities was observed with decreasing RF voltage

Summary

Introduction

Proton transfer reaction mass spectrometry (PTR-MS) is an analytical technique that allows real-time monitoring of volatile organic compounds (VOCs) at low concentrations. Brown et al [11] reported that in this instrument, ion-focusing and proton transfer reaction both occurred in the IF region. This resulted in vastly different sensitivities for different compounds and in unusual fragmentation patterns.

Objectives

Methods

Results

Discussion

Conclusion