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

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.

High‐resolution mass spectrometry exhalome profiling with a modified direct analysis in real time ion source

“…For compound identification, theoretical formulas were derived using the “elemental composition” function in the Xcalibur software. The most likely substance category and major components in breath sample can be narrowed from related literature reports 37,38 . High‐resolution mass data and known standards played important roles in verifying the compound assignments in this work.…”

“…The most likely substance category and major components in breath sample can be narrowed from related literature reports. 37,38 High-resolution mass data and known standards played important roles in verifying the compound assignments in this work. Moreover, there was no cross-contamination observed between multiple breaths.…”

Increased Sensitivity in Proton Transfer Reaction Mass Spectrometry by Using a Novel Focusing Quadrupole Ion Funnel

“…A detailed comparison of the FQ-IF drift tube and the IF drift tube in the literature is given in Table S1. As shown in Table S1, the FQ-IF drift tube is composed of a series of equally spaced electrodes with gradually decreasing inner diameters, which is similar to the structures in the literature. ,,, However, unlike a traditional IF, the novel FQ-IF drift tube consists of many quadrupole electrodes instead of ring electrodes (as seen in Figure ). In Figure S1, we can see that a single ring electrode has no ion-focusing effect, but a layer of quadrupole electrodes has an obvious ion-focusing effect.…”

“…To improve the transmission efficiency, researchers have made some good improvements to the drift tube in recent years, for example, an ion funnel (IF), PTR3, and a focusing ion molecular reactor (FIMR). The IF is a typical ion-focusing technique applied in PTR-MS in 2012 and could enhance the sensitivity by 1 to 2 orders of magnitude. , PTR3 is operated at a higher pressure (50–80 mbar), uses a tripole with radio frequency (RF) voltages to prevent ion divergence, and relies on a large sampling flow to transport ions, thus allowing for much longer reaction times and more product ions . The FIMR uses a quadrupole RF field to collimate ions onto the central axis and improves the detection sensitivity by a factor of 10 .…”

On the development of a new prototype PTR-ToF-MS instrument and its application to the detection of atmospheric amines

“…This loss in sensitivity can partly be compensated for by placing an ion funnel at the end of the DT (Barber et al, 2012). Such an ion funnel is routinely installed nowadays in most Ionicon analyzers (Pugliese et al, 2020). In the FIMR, a focusing quadrupole field acts over the entire drift region, which minimizes ion losses and boosts the instrument sensitivity (10 3 − 10 4 cps ppbv −1 ; Krechmer et al, 2018).…”