Proton transfer reaction mass technique

In general, any analytical equipment or procedure used in the field of natural products chemistry and environmental engineering is also helpful in aroma analysis 64,65 The history and principles of such art are described in detail elsewhere and will not be featured here. Gas chromatography (GC), GC-mass spectrometry (MS), and nuclear magnetic resonance (NMR) are the most frequently used techniques along with rather specialized setups such as proton transfer reaction-mass spectrometry66 (PTR-MS) used in retronasal aroma analysis (see Chapters 9.02, 9.06, 9.10-9.11). 

However, the desire to reduce or even eliminate the required sample preparation has led to the development of newer techniques, such as proton-transfer-reaction mass spectrometry (PTR-MS) and selected ion flow tube mass spectrometry coupled with ion mobility spectrometry (MS-SIFT IMS). These techniques allow real-time measurements within a single second. This enables analysis of gas composition during technological processes, monitoring of indoor air, and investigation of VOCs emitted by living organisms. 

More experiments are needed to determine the yields of reactive oxygenated intermediates formed in aromatic degradation. Ideally these would be carried out with high time resolution as an aid to distinguishing primary and secondary oxidation products. Sensitive, on-line analytical techniques, such as proton-transfer-reaction mass spectrometry, should be employed to detect and quantify such intermediates in chamber experiments carried out under NOx conditions representative of atmospheric levels. 

Recently, a variety of sulfijr- and selenium-bearing compounds were identified through the use of GC/MS techniques [51-53], element specific technique of gas chromatography with atomic emission detection (GC-AED) [54], and by proton-transfer-reaction mass spectrometry (PTR-MS)[55] in the breath of persons after the ingestion of garlic. 

Proton transfer reaction mass spectrometry (PTR-MS) was first developed at the Institute of Ion Physics of Innsbruck University in the 1990s. Nowadays, PTR-MS is a well-developed and commercially available technique for the on-line monitoring of trace volatile organic compounds (VOCs) down to parts per trillion by volume (ppt) level. PTR-MS has some advantages such as rapid response, soft chemical ionization (Cl), absolute quantification, and high sensitivity. In general, a standard PTR-MS instrument consists of external ion source, drift tube, and mass analysis detection system. Figure... 

Investigation of volatile compounds in two raspberry cultivars by two headspace techniques solid-phase microextraction/gas chromatography-mass spectrometry (SPME/GC-MS) and proton-transfer reaction-mass spectrometry (PTR-MS). Journal of Agricultural and Food Chemistry, 57,4011-4018. 

Those are, for instance, known as active chemical ionization mass spectrometry (ACIMS) for atmospheric trace-gas measurements in the chemosphere, proton transfer reaction mass spectrometry (PRT-MS), selected ion flow tube mass spectrometry (SIFT-MS), ion-molectrle reaction mass spectrometry (IMR-MS), ion attachment mass spectrometry (lAMS), and ion mobility spectroscopy (IMS). Those have now become part of the exterrsive resources of experimental techniques dedicated to all the scientific fields, especially such as fundamentals of gas-phase ion kinetics and thermochentistry, physical organic chemistry, atmospheric chemistry, interstellar chemistry, plasma, and combustion chemistry, radiation chemistry, analytical chemistry, and irltimately even medicine and biology. 

By combining the principles of PICI with an apparatus derived from selected-ion flow tube (SIFT) experiments, the technique of proton transfer reaction mass spectrometry (PTR-MS) has been developed as a dedicated tool for the analysis of volatile organic compounds (VOCs) at parts-per-trillion by volume (pptv) level in air [51,52]. PTR-MS is highly useful as a fast and quantitative method for the determination of VOCs as proven by numerous applications in food control, envi-... 

The use of reagents such as NO +, O2 and Kr + moves us into a realm beyond the strict definition of proton transfer reaction mass spectrometry, but this additional flexibility in the means of analyte ionization does have the potential to broaden the scope of the technique and, in the case of Kr +, rather dramatically so. With the availability of several alternative ionizing reagents it would be more appropriate to refer to the technique as chemical ionization reaction mass spectrometry (CIR-MS) than PTR-MS. Indeed the former term has already been used in the research literature when referring to the availability of H3O+, NO+ and O2 reagent ions from a single source in a PTR-MS instrument [16]. However, the term PTR-MS is now well established in the literature and at present there seems to be no widespread desire to change to CIR-MS. 

Pozo-Bay6n, M.-A., Santos,M.,Martfn-Alvarez, P. J., Reineccius,G. (2009) Influence of carbonation on aroma release from liquid systems using an artificial throat and a proton transfer reaction-mass spectrometric technique (PTR-MS). Flavor Fragr. J. 24, 226. 

Steeghs, M. (2007) Development of proton-transfer reaction mass spectrometry techniques. Detection of trace gases in biology and medicine. PhD thesis. Radboud University Nijmegen, Netherlands. 

Ezra, D., Jasper, J., Rogers, T. et al. (2004) Proton transfer reaction-mass spectrometry as a technique to measure volatile emissions of Muscodor albus. Plant Sci. 166,1471. 

The better analyze the problem and control production and products, many analytical techniques were perfected, most are based on headspace gas chromatography, " but proton transfer reaction mass spectrometry have also been used. ... 

Fig. 15.14 Analytical techniques for time-resolved headspace analysis. An electronic nose can be used as a low-cost process-monitoring device, where chemical information is not mandatory. Electron impact ionisation mass spectrometry (EI-MS) adds sensitivity, speed and some chemical information. Yet, owing to the hard ionisation mode, most chemical information is lost. Proton-transfer-reaction MS (PTR-MS) is a sensitive one-dimensional method, which provides characteristic headspace profiles (detailed fingerprints) and chemical information. Finally, resonance-enhanced multiphoton ionisation (REMPI) TOFMS combines selective ionisation and mass separation and hence represents a two-dimensional method. (Adapted from [190])...

A knowledge of the gas-phase thermochemistry of ions and neutrals is important in mass spectrometry. This is particularly true for those ionization techniques (such as Cl) involving proton transfer reactions in the gas phase which result in the formation of pseudomol-... 

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