Progress in SIFT‐MS: Breath analysis and other applications

Abstract

The development of selected ion flow tube mass spectrometry, SIFT-MS, is described from its inception as the modified very large SIFT instruments used to demonstrate the feasibility of SIFT-MS as an analytical technique, towards the smaller but bulky transportable instruments and finally to the current smallest Profile 3 instruments that have been located in various places, including hospitals and schools to obtain on-line breath analyses. The essential physics and engineering principles are discussed, which must be appreciated to design and construct a SIFT-MS instrument. The versatility and sensitivity of the Profile 3 instrument is illustrated by typical mass spectra obtained using the three precursor ions H(3)O(+), NO(+) and O(2)(+)·, and the need to account for differential ionic diffusion and mass discrimination in the analytical algorithms is emphasized to obtain accurate trace gas analyses. The performance of the Profile 3 instrument is illustrated by the results of several pilot studies, including (i) on-line real time quantification of several breath metabolites for cohorts of healthy adults and children, which have provided representative concentration/population distributions, and the comparative analyses of breath exhaled via the mouth and nose that identify systemic and orally-generated compounds, (ii) the enhancement of breath metabolites by drug ingestion, (iii) the identification of HCN as a marker of Pseudomonas colonization of the airways and (iv) emission of volatile compounds from urine, especially ketone bodies, and from skin. Some very recent developments are discussed, including the quantification of carbon dioxide in breath and the combination of SIFT-MS with GC and ATD, and their significance. Finally, prospects for future SIFT-MS developments are alluded to.

Determination of the Deuterium Abundances in Water from 156 to 10,000 ppm by SIFT-MS

“…The percentages (I) of the minor isotopologues of H 9 O 4 + ions from the total concentration of all possible isotopologues calculated as a function of R 1 , the equilibrium abundance of D in the water vapour in the helium carrier gas, as calculated by using Eqs. (2) [12,22,23]. The flow rate of sampled air was configured such that the flow tube pressure in the absence of He carrier gas was about 0.15 Torr and then the experiments were carried out with total flow tube pressure of sample and carrier gas of about 1 Torr.…”

“…Subsequently, these methods were adapted as the gas-phase analytical mass spectrometric techniques SIFT-MS and FA-MS. SIFT-MS has been used to measure trace gas concentrations in air samples down to the parts per billion (ppb) level and below [11,12] and is proving to be especially valuable for on-line, real-time analyses of exhaled breath. Our first exploratory studies on the measurement of the deuterium abundance in water vapour were carried out using an early SIFT-MS instrument of low sensitivity [1].…”

From molecules in space to molecules in breath

“…Some of the trace compounds detected and quantified in breath by SIFT-MS are indicated in Figure 1. The association of particular trace metabolites with disease states are also indicated together with the concentration reference ranges for ostensibly healthy individuals resulting from longitudinal inter-individual and intra-individual studies [4,5]. Careful scrutiny of Figure 1 reveals that the trace biomarkers are present in concentrations ranging from sub-ppbv (parts-per-billion by volume) to a few ppmv (parts-per-million by volume), i.e.…”

“…Breath is exhaled at the sample entry port of the SIFT-MS; on inhalation, the ambient air is sampled and analysed, as is important in breath analysis research. Details of the SIFT-MS method, the physics and ion chemistry involved, a line diagram showing the structure of the instrumentation and its application to breath analysis, have been given in recent authoritative reviews [4,5].…”

The Use of SIFT-MS in Profiling the Faecal Volatile Metabolome in Horses with Colic: A Pilot Study

“…For this reason, other techniques have been developed, and one such technique is selected ion tube mass spectrometry, SIFT-MS. The details of this technique have been extensively covered elsewhere [3,4] so are not included here. The advantages of SIFT-MS are that it is rapid, quantitative and relatively sensitive and the data are readily converted for multivariate analysis of spectral profiles if required.…”