共查询到20条相似文献,搜索用时 15 毫秒
1.
We investigated a two-stage ion source for proton transfer reaction (PTR) ionization to achieve more selective mass spectrometric (MS) detection of selected volatile organic compounds (VOCs) than that achieved with commonly used PTR-MS instruments, which are based on single-step PTR ionization with H3O+. The two-stage PTR ion source generated reagent ions other than H3O+ by an initial PTR between H3O+ and a selected VOC, and then a second PTR ionization occurred only for VOCs with proton affinities larger than the affinity of the reagent VOC. Acetone and acetonitrile were useful as reagent VOCs because they provided dominant peaks as a protonated form. Using two-stage PTR-MS, we differentiated isomeric VOCs (for example, ethyl acetate and 1,4-dioxane) by means of differences in their proton affinities; protonated acetone formed the [M + H]+ ion from ethyl acetate but not from 1,4-dioxane. The PTR-MS-derived concentrations agreed quantitatively with those independently determined by Fourier transform infrared spectroscopy (FT-IR) at parts per million by volume (ppmv) levels. In addition, interfering fragment ions formed from alkyl benzenes at m/z 79 (C6H7+) could be distinguished from the m/z 79 ion arising from protonation of benzene, and therefore this method would prevent overestimation of benzene concentrations in air samples in which both benzene and alkyl benzenes are present. This two-stage PTR ionization may be useful for distinguishing various isomeric species, including aldehydes and ketones, if appropriate reagent ions are selected. 相似文献
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Jorge Ivn Salazar Gmez Christian Klucken Martha Sojka Liudmyla Masliuk Thomas Lunkenbein Robert Schlgl Holger Ruland 《Journal of mass spectrometry : JMS》2019,54(12):987-1002
We present an effective procedure to differentiate instrumental artefacts, such as parasitic ions, memory effects, and real trace impurities contained in inert gases. Three different proton transfer reaction mass spectrometers were used in order to identify instrument‐specific parasitic ions. The methodology reveals new nitrogen‐ and metal‐containing ions that up to date have not been reported. The parasitic ion signal was dominated by [N2]H+ and [NH3]H+ rather than by the common ions NO+ and O2+. Under dry conditions in a proton transfer reaction quadrupole interface time‐of‐flight mass spectrometer (PTR‐QiTOF), the ion abundances of [N2]H+ were elevated compared with the signals in the presence of humidity. In contrast, the [NH3]H+ ion did not show a clear humidity dependency. On the other hand, two PTR‐TOF1000 instruments showed no significant contribution of the [N2]H+ ion, which supports the idea of [N2]H+ formation in the quadrupole interface of the PTR‐QiTOF. Many new nitrogen‐containing ions were identified, and three different reaction sequences showing a similar reaction mechanism were established. Additionally, several metal‐containing ions, their oxides, and hydroxides were formed in the three PTR instruments. However, their relative ion abundancies were below 0.03% in all cases. Within the series of metal‐containing ions, the highest contribution under dry conditions was assigned to the [Fe(OH)2]H+ ion. Only in one PTR‐TOF1000 the Fe+ ion appeared as dominant species compared with the [Fe(OH)2]H+ ion. The present analysis and the resulting database can be used as a tool for the elucidation of artefacts in mass spectra and, especially in cases, where dilution with inert gases play a significant role, preventing misinterpretations. 相似文献
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C.A. Mayhew P. Sulzer F. Petersson S. Haidacher A. Jordan L. Märk P. Watts T.D. Märk 《International journal of mass spectrometry》2010,289(1):58-63
Using recent developments in proton transfer reaction mass spectrometry, proof-of-principle investigations are reported here to illustrate the capabilities of detecting solid explosives in real-time. Two proton transfer reaction time-of-flight mass spectrometers (Ionicon Analytik) have been used in this study. One has an enhanced mass resolution (m/Δm up to 8000) and high sensitivity (~50 cps/ppbv). The second has enhanced sensitivity (~250 cps/ppbv) whilst still retaining high resolution capabilities (m/Δm up to 2000). Both of these instruments have been successfully used to identify solid explosives (RDX, TNT, HMX, PETN and Semtex A) by analyzing the headspace above small quantities of samples at room temperature and from trace quantities not visible to the naked eye placed on surfaces. For the trace measurements a simple pre-concentration and thermal desorption technique was devised and used. Importantly, we demonstrate the unambiguous identification of threat agents in complex chemical environments, where multiple threat agents and interferents may be present, thereby eliminating false positives. This is of considerable benefit to security and for the fight against terrorism. 相似文献
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Wieland F Gloess AN Keller M Wetzel A Schenker S Yeretzian C 《Analytical and bioanalytical chemistry》2012,402(8):2531-2543
A real-time automated process control tool for coffee roasting is presented to consistently and accurately achieve a targeted
roast degree. It is based on the online monitoring of volatile organic compounds (VOC) in the off-gas of a drum roaster by
proton transfer reaction time-of-flight mass spectrometry at a high time (1 Hz) and mass resolution (5,500 m/Δm at full width
at half-maximum) and high sensitivity (better than parts per billion by volume). Forty-two roasting experiments were performed
with the drum roaster being operated either on a low, medium or high hot-air inlet temperature (= energy input) and the coffee
(Arabica from Antigua, Guatemala) being roasted to low, medium or dark roast degrees. A principal component analysis (PCA)
discriminated, for each one of the three hot-air inlet temperatures, the roast degree with a resolution of better than ±1
Colorette. The 3D space of the three first principal components was defined based on 23 mass spectral profiles of VOCs and
their roast degree at the end point of roasting. This provided a very detailed picture of the evolution of the roasting process
and allowed establishment of a predictive model that projects the online-monitored VOC profile of the roaster off-gas in real
time onto the PCA space defined by the calibration process and, ultimately, to control the coffee roasting process so as to
achieve a target roast degree and a consistent roasting. 相似文献
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Miyaji H Gasser G Green SJ Molard Y Strawbridge SM Tucker JH 《Chemical communications (Cambridge, England)》2005,(42):5355-5357
Ferrocene-containing amidopyridine receptors bind carboxylic acids and the amino acid phenylalanine in acetonitrile via a novel proton transfer process that enables guests to be electrochemically sensed by positive shifts in the ferrocene-centred redox potentials. 相似文献
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Del Pulgar JS Soukoulis C Biasioli F Cappellin L García C Gasperi F Granitto P Märk TD Piasentier E Schuhfried E 《Talanta》2011,85(1):386-393
In the present study, the recently developed proton transfer reaction time of flight mass spectrometry (PTR-ToF-MS) technique was used for the rapid characterization of dry cured hams produced according to 4 of the most important Protected Designations of Origin (PDOs): an Iberian one (Dehesa de Extremadura) and three Italian ones (Prosciutto di San Daniele, Prosciutto di Parma and Prosciutto Toscano). In total, the headspace composition and respective concentration for nine Spanish and 37 Italian dry cured ham samples were analyzed by direct injection without any pre-treatment or pre-concentration. Firstly, we show that the rapid PTR-ToF-MS fingerprinting in conjunction with chemometrics (Principal Components Analysis) indicates a good separation of the dry cured ham samples according to their production process and that it is possible to set up, using data mining methods, classification models with a high success rate in cross validation. Secondly, we exploited the higher mass resolution of the new PTR-ToF-MS, as compared with standard quadrupole based versions, for the identification of the exact sum formula of the mass spectrometric peaks providing analytical information on the observed differences. The work indicates that PTR-ToF-MS can be used as a rapid method for the identification of differences among dry cured hams produced following the indications of different PDOs and that it provides information on some of the major volatile compounds and their link with the implemented manufacturing practices such as rearing system, salting and curing process, manufacturing practices that seem to strongly affect the final volatile organic profile and thus the perceived quality of dry cured ham. 相似文献
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Influence of internal standard charge state on the accuracy of mass measurements in orthogonal acceleration time-of-flight mass spectrometers 总被引:1,自引:0,他引:1
Charles L 《Rapid communications in mass spectrometry : RCM》2008,22(2):151-155
Accuracy of mass measurements performed in orthogonal acceleration time-of-flight (oa-TOF) mass spectrometers highly depends on the quality of the signal and the internal calibration. The use of two reference compounds which bracket the targeted unknown, give rise to ions with sufficient signal-to-noise ratio while avoiding detector saturation and produce signals of similar intensity as compared to the target is a common requirement which allow a 5 ppm accuracy on a routine basis. Ion charge state is demonstrated here to be an additional and particularly critical parameter. Using internal references of lower charge state than the target ion systematically yielded overestimated data. Errors measured for quadruply charged molecules were in the range 16-18 ppm when mass calibrants were singly charged ions while accuracy was below 5 ppm when references and target ions were in the same charge state. Magnitude of errors was found to increase with the difference in charge state. This phenomenon arises from the orthogonal acceleration of ions in the TOF analyzer, an interface implemented in all TOF mass spectrometers to accommodate continuous beam ionization sources. Copyright (c) 2007 John Wiley & Sons, Ltd. 相似文献
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Agarwal B Petersson F Jürschik S Sulzer P Jordan A Märk TD Watts P Mayhew CA 《Analytical and bioanalytical chemistry》2011,400(8):2631-2639
The first reported use of proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) for the detection of a range
of illicit and prescribed drugs is presented here. We describe the capabilities of PTR-TOF-MS to detect the following commonly
used narcotics—ecstasy (N-methyl-3,4-methylenedioxyamphetamine), morphine, codeine, cocaine and heroin—by the direct sampling of the headspace above
small solid quantities (approximately 50 mg) of the drugs placed in glass vials at room temperature, i.e. with no heating
of the sample and no pre-concentration. We demonstrate in this paper the ability to identify the drugs, both illicit and prescribed,
using PTR-TOF-MS through the accurate m/z assignment of the protonated parent molecule to the second decimal place. We have also included in this study measurements
with an impure sample of heroin, containing typical substances found in “street” heroin, to illustrate the use of the technology
for more “real-world” samples. Therefore, in a real-world complex chemical environment, a high level of confidence can be
placed on the detection of drugs. Although the protonated parent is observed for all drugs, the reactant channel leading to
this species is not the only one observed and neither is it necessarily the most dominant. Details on the observed fragmentation
behaviour are discussed and compared to electrospray ionisation MSn studies available in the literature. 相似文献
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Chow E Wong EL Pascoe O Hibbert DB Gooding JJ 《Analytical and bioanalytical chemistry》2007,387(4):1489-1498
Multiple electrodes, combined with a chemometric strategy to calibrate the measurement response, have been used for the determination
of an analyte across a broader dynamic range than is possible with a single electrode. The model system used for the detection
of copper comprised electrodes modified with a self-assembled monolayer. The electrodes were modified with the copper-complexing
species (3-mercaptopropionic acid, thioctic acid, and the peptides cysteine and Gly-Gly-His) and copper was determined over
concentrations ranging from nanomolar to millimolar using voltammetric analysis. We have demonstrated that by combining the
calibration functions from the four electrodes a better estimate (i.e. with smaller variance) of the concentration of the
analyte is obtained. Measurement uncertainty is expressed for independently prepared electrodes, which allows the possibility
of commercial production and factory calibration. The principles of using multiple electrodes modified with recognition elements
with different affinities for the target analyte to extend the dynamic range of sensors is a general one that could be applied
to other analytes. 相似文献
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Galvani M Hamdan M Righetti PG Gelfi C Sebastiano R Citterio A 《Rapid communications in mass spectrometry : RCM》2001,15(3):210-216
Quaternized piperazine ((N-methyl-N-omega-iodobutyl-N'-methyl)piperazine; QPzl) is a novel compound described as an ideal coating material for the silica capillaries that are commonly used for capillary zone electrophoresis. In the course of such analysis, contact between such coatings and biomolecules may result in certain modifications of the latter. To gain specific information on such potential modifications, solutions at pH 10.0 containing both QPzl and standard proteins/peptides were incubated for various periods and examined by matrix-assisted laser desorption/ionisation mass spectrometry. The reduction of the S-S bridges, denaturation in 8 M urea, the isoelectric point of the protein and the duration of the incubation had a profound influence on the investigated reaction. Analysis in reflectron mode and post source decay identified Cys as the likely site of interaction. The implications of the present measurements for proteome analysis using capillary and gel electrophoresis are discussed. 相似文献
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《Journal of mass spectrometry : JMS》2017,52(1):30-35
We examine the potential for PTR‐TOF‐MS systems to quantitatively measure glyoxal in ambient air by characterizing the response of the instrument to a dilute glyoxal sample, calibrating the system as a function of humidity. The concentration of glyoxal in a sample air‐stream was measured with an UV absorption spectrometer in parallel to a PTR‐TOF‐MS. This calibration demonstrated that the PTR‐TOF‐MS has a relatively low sensitivity to glyoxal particularly at high humidity. Extensive fragmentation of glyoxal to formaldehyde was observed. This behaviour not only desensitizes PTR‐MS system to glyoxal; it may also pose a problem to the quantification of formaldehyde. © 2016 The Authors. Journal of Mass Spectrometry Published by John Wiley & Sons Ltd. 相似文献