Account: On the Features, Successes and Challenges of Selected Ion Flow Tube Mass Spectrometry

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Infection by Pseudomonas aeruginosa (PA) is a major cause of morbidity and mortality in patients with cystic fibrosis (CF). Breath analysis could potentially be a useful diagnostic of such infection, and analyses of volatile organic compounds (VOCs) emitted from PA cultures are an important part of the search for volatile breath markers of PA lung infection. Our pilot experiments using solid-phase microextraction, SPME and gas chromatography/mass spectrometric (GC/MS) analyses of volatile compounds produced by PA strains indicated a clear presence of methyl thiocyanate. This provided a motivation to develop a method for real-time online quantification of this compound by selected ion flow tube mass spectrometry, SIFT-MS. The kinetics of reactions of H(3)O(+), NO(+) and O(2)(+•) with methyl thiocyanate at 300 K were characterized and the characteristic product ions determined (proton transfer for H(3)O(+), rate constant 4.6 × 10(-9) cm(3) s(-1); association for NO(+), 1.7 × 10(-9) cm(3) s(-1) and nondissociative charge transfer for O(2)(+•) 4.3 × 10(-9) cm(3) s(-1)). The kinetics library was extended by a new entry for methyl thiocyanate accounting for overlaps with isotopologues of hydrated hydronium ions. Solubility of methyl thiocyanate in water (Henry's law constant) was determined using standard reference solutions and the linearity and limits of detection of both SIFT-MS and SPME-GC/MS methods were characterized. Thirty-six strains of PA with distinct genotype were cultivated under identical conditions and 28 of them (all also producing HCN) were found to release methyl thiocyanate in headspace concentrations greater than 6 parts per billion by volume (ppbv). SIFT-MS was also used to analyze the breath of 28 children with CF and the concentrations of methyl thiocyanate were found to be in the range 2-21 ppbv (median 7 ppbv).

Section: Sift-ms Determination Of Henry's Law Constantmentioning

confidence: 99%

Section: Sift-ms Determination Of Henry's Law Constantmentioning

confidence: 99%

Quantification of methyl thiocyanate in the headspace of Pseudomonas aeruginosa cultures and in the breath of cystic fibrosis patients by selected ion flow tube mass spectrometry

Shestivská

Nemec

Dřevı́nek

et al. 2011

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“…The SIFT-MS analytical technique for sampling liquid headspace has been described in detail in several research and review papers, [6,7,9,[21][22][23] and need not be repeated here. It is Table 1.…”

Section: Sift-msmentioning

confidence: 99%

Time‐resolved selected ion flow tube mass spectrometric quantification of the volatile compounds generated by E. coli JM109 cultured in two different media

Chippendale

Španěl

Smith

2011

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Preliminary measurements have been made of the volatile compounds emitted by the bacterium E. coli JM109 cultured in the commonly used media Dulbecco's modified Eagle's medium (DMEM) and lysogeny broth (LB) using selected ion flow tube mass spectrometry, SIFT-MS, as a step towards the real time, non-invasive monitoring of accidental infections of mammalian cell cultures. In one procedure, the culture medium alone and the E. coli cells/medium combination were held at 37 °C in bottles sealed with septa for a given time period, usually overnight, to allow the bacterium to proliferate, after which the captured headspace was analysed directly by SIFT-MS. Several compounds were seen to be produced by the E. coli cells that depended on the liquid medium used: when cultured in DMEM, copious amounts of ethanol, acetaldehyde and hydrogen sulphide were produced; in LB ammonia is the major volatile product. In a second procedure, to ensure aerobic conditions prevailed in the cell culture, selected volatile compounds were monitored by SIFT-MS in real time for several hours above the open-to-air E. coli/DMEM culture held at close to 37 °C. The temporal variations in the concentrations of some compounds, which reflect their production rates in the culture, indicate maxima. Thus, the maxima in the ethanol and acetaldehyde production are a reflection of the reduction of glucose from the DMEM by the vigorous E. coli cells and the maximum in the hydrogen sulphide level is an indication of the loss of the sulphur-bearing amino acids from the DMEM. Serendipitously, emissions from DMEM inadvertently infected with the bacterium C. testosteroni were observed when large quantities of ammonia were seen to be produced. The results of this preliminary study suggest that monitoring volatile compounds might assist in the early detection of bacterial infection in large-scale bioreactors.

“…SIFT‐MS technology uses softer chemical ionization than PTR‐MS due to the lower pressure of the carrier gas in the flow tube (about 0.4 vs 1.5 Torr, respectively). In the SIFT‐MS technique no electric field is employed (in contrast to PTR‐MS) and it is thus possible to carry out ion–molecule reactions under thermal conditions where the kinetic behaviour is well known . The other fundamental difference between these two techniques is that SIFT‐MS instruments can generate eight reagent ions (H 3 O + , O 2 + , NO + , O •− , O 2 •− , OH − , NO 2 − and NO 3 − ) as standard in the microwave discharge plasma.…”

Section: Introductionmentioning

confidence: 99%

Direct analysis of aldehydes and carboxylic acids in the gas phase by negative ionization selected ion flow tube mass spectrometry: Quantification and modelling of ion–molecule reactions

Ghislain

Costarramone

Sotiropoulos

et al. 2019

Rationale The concentrations of aldehydes and volatile fatty acids have to be controlled because of their potential harmfulness in indoor air or relationship with the organoleptic properties of agri‐food products. Although several specific analytical methods are currently used, the simultaneous analysis of these compounds in a complex matrix remains a challenge. The combination of positive and negative ionization selected ion flow tube mass spectrometry (SIFT‐MS) allows the accurate, sensitive and high‐frequency analysis of complex gas mixtures of these compounds. Methods The ion–molecule reactions of negative precursor ions (OH−, O•−, O2•−, NO2− and NO3−) with five aldehydes and four carboxylic acids were investigated in order to provide product ions and rate constants for the quantification of these compounds by negative ion SIFT‐MS. The results were compared with those obtained by conventional analysis methods and/or with already implemented SIFT‐MS positive ionization methods. The modelling of hydroxide ion (OH−)/molecule reaction paths by ab‐initio calculation allowed a better understanding of these gas‐phase reactions. Results Deprotonation systematically occurs by reaction between negative ions and aldehydes or acids, leading to the formation of [M − H]− primary ions. Ab‐initio calculations demonstrated the α‐CH deprotonation of aldehydes and the acidic proton abstraction for fatty acids. For aldehydes, the presence of water in the flow tube leads to the formation of hydrated ions, [M − H]−.H2O. With the NO2− precursor ion, a second reaction channel results in ion–molecule association with the formation of M.NO2− ions. Conclusions Except for formaldehyde, all the studied compounds can be quantified by negative ion SIFT‐MS with significant rate constants. In addition to positive ion SIFT‐MS with H3O+, O2+ and NO+ precursor ions, negative ionization with O•−, O2•−, OH−, NO2− and NO3− extends the range of analysis of aldehydes and carboxylic acids in air without a preparation or separation step. This methodology was illustrated by the simultaneous quantification in single‐scan experiments of seven aldehydes and six carboxylic acids released by building materials.