Selected Ion Flow-Drift Tube Mass Spectrometry: Quantification of Volatile Compounds in Air and Breath

Abstract

A selected ion flow drift tube mass spectrometric analytical technique, SIFDT-MS, is described that extends the established selected ion flow tube mass spectrometry, SIFT-MS, by the inclusion of a static but variable E-field along the axis of the flow tube reactor in which the analytical ion-molecule chemistry occurs. The ion axial speed is increased in proportion to the reduced field strength E/N (N is the carrier gas number density) and the residence/reaction time, t, which is measured by Hadamard transform multiplexing, is correspondingly reduced. To ensure a proper understanding of the physics and ion chemistry underlying SIFDT-MS, ion diffusive loss to the walls of the flow-drift tube and the mobility of injected H3O+ ions have been studied as a function of E/N. It is seen that the derived diffusion coefficient and mobility of H3O + ions are consistent with those previously reported. The rate coefficient has been determined at elevated E/N for the association reaction of the H3O + reagent ions with H2O molecules, which is the first step in the production of H3O + (H2O)1,2,3 reagent hydrate ions. The production of hydrated analyte ion was also experimentally investigated. The analytical performance of SIFDT-MS is demonstrated by the quantification of acetone and isoprene in exhaled breath. Finally, the essential features of SIFDT-MS and SIFT-MS are compared, notably pointing out that a much lower speed of the flow-drive pump is required for SIFDT-MS, which facilitates development of smaller cost-effective analytical instruments for real time breath and fluid headspace analyses.

Volatile compounds profiling by using proton transfer reaction‐time of flight‐mass spectrometry (PTR‐ToF‐MS). The case study of dark chocolates organoleptic differences

“…Former SIFDT instruments had severe drawbacks (complex experimental setup, poor sensitivity linked to important dilution with an inert carrier gas) although they were the basis for developing proton transfer reaction (PTR) instruments (see below). New developments should lower the limits of detection and of quantification in reduced size SIFDT instruments . As absolute quantification of ions is possible through fine control of experimental conditions, SIFT‐MS has been used extensively to study the chemistry of IMRs, and determining k‐rate coefficients.…”

In‐tube collision‐induced dissociation for selected ion flow‐drift tube mass spectrometry, SIFDT‐MS: a case study of NO+ reactions with isomeric monoterpenes

“…The experiments were carried out using a recently constructed laboratory apparatus for selected ion flow drift tube mass spectrometry, SIFDT‐MS . This technique is based on the soft chemical ionisation of neutral reactant molecules with selected reagent ions H 3 O + , NO + or O 2 +• in the flow‐drift tube reactor.…”

“…The important improvement is that the reaction time needed for this calculation is routinely and precisely measured using the Hadamard transformation . The construction of the SIFDT‐MS instrument and principles of its operation were described in detail in recent papers …”

“…Unfortunately, such potential difference cannot be easily applied in the current commercial SIFT‐MS instruments due to restricted ranges of quadrupole mass spectrometer axis potential. We have thus decided to investigate the possibilities offered by in‐tube CID using the newly constructed selected ion flow‐drift tube SIFDT instrument …”

Volatile compounds released by Nalophan; implications for selected ion flow tube mass spectrometry and other chemical ionisation mass spectrometry analytical methods

“…Although various analytical techniques are available for the on‐line real‐time analysis of exhaled breath for volatile organic compounds (VOCs), e.g. selected ion flow tube mass spectrometry (SIFT‐MS), selected ion flow‐drift tube (SIFDT‐MS), proton transfer reaction mass spectrometry (PTR‐MS), secondary electrospray ionisation mass spectrometry (SESI‐MS), ion mobility spectrometry (IMS), absorption spectroscopy and sensors, off‐line analyses are still important. This is because longer analyte ion integration times can be used to improve analytical sensitivity and it is not always practical to move the instrument on‐site.…”