Electron capture mass spectrometry of organic environmental contaminants

A pulsed large-volume injection gas chromatography coupled with electron-capture negative ionization quadrupole mass spectrometry (pLVI-GC/ECNI-qMS) was developed for the simultaneous determination of typical halogenated persistent organic pollutants (H-POPs). By monitoring the characteristic ions of large mass-to-charge ratio (m/z) for each of the H-POPs rather than the chlorine and/or bromine ions, this method avoided the possible interferences arising from the H-POPs themselves and from complex matrices encountered frequently in current GC/qMS methods; and allowed, on the other hand, the use of 13 C-labeled and perdeuterated analogues as internal standards for reliable quantification. pLVI up to 120 L improved the instrumental detection limits down to pg-fg mL Ϫ1

Section: Comparison Of Ei-qms Pci-qms and Ecni-qms For Determinatiomentioning

confidence: 99%

Pulsed large volume injection gas chromatography coupled with electron-capture negative ionization quadrupole mass spectrometry for simultaneous determination of typical halogenated persistent organic pollutants

Zhao

Yang

Wang

2007

“…When resonance electron capture (EC) ionization was adapted for negative chemical ionization (NCI) mass spectrometry, methane was used as reagent gas to thermalize electrons [4][5][6]. Although more efficient gases for EC-NCI-MS have long been identified [7], methane continues to be the most popular choice [8,9].…”

Section: Introductionmentioning

confidence: 99%

Isobutane Made Practical as a Reagent Gas for Chemical Ionization Mass Spectrometry

Newsome

Steinkamp

Giordano

2016

Abstract. As a reagent gas for positive-and negative-mode chemical ionization mass spectrometry (CI-MS), isobutane (i-C 4 H 10 ) produces superior analyte signal abundance to methane. Isobutane has never been widely adopted for CI-MS because it fouls the ion source more rapidly and produces positive CI spectra that are more strongly dependent on reagent gas pressure compared with methane. Isobutane was diluted to various concentrations in argon for use as a reagent gas with an unmodified commercial gas chromatograph-mass spectrometer. Analyte spectra were directly compared using methane, isobutane, and isobutane/argon mixtures. A mixture of 10% i-C 4 H 10 in argon produced twice the positive-mode analyte signal of methane, equal to pure isobutane, and reduced spectral dependence on reagent gas pressure. Electron capture negative chemical ionization using 1% i-C 4 H 10 in argon tripled analyte signal compared with methane and was reproducible, unlike pure isobutane. The operative lifetime of the ion source using isobutane/ argon mixtures was extended exponentially compared with pure isobutane, producing stable and reproducible CI signal throughout. By diluting the reagent gas in an inert buffer gas, isobutane CI-MS experiments were made as practical to use as methane CI-MS experiments but with superior analytical performance.

“…The immediate need for this novel, laser-driven soft ionization source is for the analysis of single atmospheric organic particles, although there are many different areas in which such a soft, pulsed ionization source would be extremely beneficial. These include environmental analysis [14], charge transfer reactions [15], and cluster analysis [16].…”

mentioning

confidence: 99%

Photoelectron resonance capture ionization (PERCI): A novel technique for the soft-ionization of organic compounds

LaFranchi

Petrucci

2004

Photoelectron resonance capture ionization (PERCI) is demonstrated as a sensitive ionization technique involving minimal fragmentation of organic molecules. PERCI has been used successfully to softly and efficiently ionize both strongly UV absorbing and non-absorbing molecules. Tunable low energy (Ͻ1 eV) electrons are generated by focusing a pulsed UV laser on an aluminum photocathode in the presence of gas phase analyte. Negative ions are formed through a resonance electron capture process. Mass analysis is done using a reflectron time-of-flight mass spectrometer. PERCI is demonstrated for a number of gas phase compounds and simple mixtures, including sulfur hexafluoride, nitrobenzene, nitrophenol, 2-pentanone, hexanal, heptanal, and octanal. In all cases the molecular ion (or [M Ϫ H] Ϫ ) was observed to be the dominant peak. The 1 limit of detection was estimated to be on the order of 10 6 molecules in the ionization region. . It has been shown that the result of low energy electron attachment depends heavily upon the electron energy [1]. For instance, at a particular electron energy ( ), associative attachment can occur leaving the molecular anion radical present. At a different , dissociative electron attachment can occur in which the molecule breaks apart to give a neutral radical species and a fragment anion. The favored pathway is also a function of the structural and electronic properties of the molecule. The electron capture phenomenon, known as resonance electron capture (REC), has proved to be a very useful ionization method for the detection of a variety of classes of organic compounds by mass spectrometry. It has been shown to efficiently ionize organic molecules functionalized with halogens, nitrates, sulfur, conjugated -systems and carbonyls [2][3][4][5], as well as straight-chain hydrocarbons with minimal functionality [6]. Most recently, the versatility of REC ionization was underlined in the literature for chromatographic detection [7].As an example of REC, the reactions at two different electron capture resonances (associative and dissociative) of nitrobenzene are shown below [8].In Reaction 1, capture of zero energy electrons is an efficient process for producing intact molecular ions. In addition, through Reaction 2, higher electron energy resonances are also available for electron capture producing the NO 2 Ϫ fragment. These higher energy resonances can improve the analytical selectivity of REC in the case of compound mixtures.Two instruments capable of REC ionization, suited for gas phase studies, are the throchoidal electron monochromator [9] and the reversal electron attachment detector (READ) [10]. The electron monochromator uses crossed electric and magnetic fields to force different trajectories on electrons with different energies. An offset exit aperture allows monoenergetic electrons to pass into the source region of a mass spectrometer. A more detailed discussion can be found in the reference by Laramee et al. [9]. READ operates by