Studies in chemical ionization mass spectrometry

Michnowicz, John; Munson, Burnaby

doi:10.1002/oms.1210040149

Cited by 46 publications

(14 citation statements)

References 17 publications

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“…If the cluster is ionized via its solvent molecules, a proton can be transferred from it to the sample molecule, driven by its higher proton affinity. The process of cluster CI is similar to standard CI,44–46 except that the hydrogen or proton transfer agents do not need to collide as they are in close proximity within the cluster. After ionization, most of the solvent molecules dissociate since the van der Waals bonds of the cluster are usually weaker than chemical bonds in the sample molecular ion.…”

Section: Cluster Chemical Ionization With Smbmentioning

confidence: 99%

Gas chromatography‐mass spectrometry with supersonic molecular beams

et al. 2008

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Gas chromatography-mass spectrometry (GC-MS) with supersonic molecular beams (SMBs) (also named Supersonic GC-MS) is based on GC and MS interface with SMBs and on the electron ionization (EI) of vibrationally cold analytes in the SMBs (cold EI) in a fly-through ion source. This ion source is inherently inert and further characterized by fast response and vacuum background filtration capability. The same ion source offers three modes of ionization including cold EI, classical EI and cluster chemical ionization (CI). Cold EI, as a main mode, provides enhanced molecular ions combined with an effective library sample identification, which is supplemented and complemented by a powerful isotope abundance analysis method and software. The range of low-volatility and thermally labile compounds amenable for analysis is significantly increased owing to the use of the contact-free, fly-through ion source and the ability to lower sample elution temperatures through the use of high column carrier gas flow rates. Effective, fast GC-MS is enabled particularly owing to the possible use of high column flow rates and improved system selectivity in view of the enhancement of the molecular ion. This fast GC-MS with SMB can be further improved via the added selectivity of MS-MS, which by itself benefits from the enhancement of the molecular ion, the most suitable parent ion for MS-MS. Supersonic GC-MS is characterized by low limits of detection (LOD), and its sensitivity is superior to that of standard GC-MS, particularly for samples that are hard for analysis. The GC separation of the Supersonic GC-MS can be improved with pulsed flow modulation (PFM) GC x GC-MS. Electron ionization LC-MS with SMB can also be combined with the Supersonic GC-MS, with fast and easy switching between these two modes of operation.

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Section: Cluster Chemical Ionization With Smbmentioning

confidence: 99%

Gas chromatography‐mass spectrometry with supersonic molecular beams

et al. 2008

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“…Alternatively, chemical ionization (CI) was developed [4][5][6] and can be used for the provision of protonated molecular ions, and CI ion sources sometimes supplement and complement EI ion sources in GC-MS. However, CI usually requires venting the GC-MS system and the manual change of the ion source; it is less sensitive than EI, and most importantly, CI is incompatible with library-based sample identification.…”

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confidence: 99%

A comparison of electron ionization mass spectra obtained at 70 eV, low electron energies, and with cold EI and their NIST library identification probabilities

2020

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Electron ionization (EI) mass spectra of 46 compounds from several different compound classes were measured. Their molecular ion abundances were compared as obtained with 70‐eV EI, with low eV EI (such as 14 eV), and with EI mass spectra of vibrationally cold molecules in supersonic molecular beams (Cold EI). We further compared these mass spectra in their National Institute of Standards and Technology (NIST) library identification probabilities. We found that Low eV EI is not a soft ionization method, and it has little or no influence on the molecular ion relative abundances for large molecules and those with weak or no molecular ions. Low eV EI for compounds with abundant or dominant molecular ions in their 70 eV mass spectra results in the reduction of low mass fragment ions abundances thereby reducing their NIST library identification probabilities thus rarely justifies its use in real‐world applications. Cold EI significantly enhances the relative abundance of the molecular ions particularly for large compounds; yet, it retains the low mass fragment ions; hence, Cold EI mass spectra can be effectively identified by the NIST library. Different standard EI ion sources provide different 70 eV EI mass spectra. Among the Agilent technologies ion sources, the “Extractor” exhibits relatively abundant molecular ions compared with the “Inert” ion source, while the “High efficiency source” (HES) provides mass spectra with depleted molecular ions compared with the “Inert” ion source or NIST library mass spectra. These conclusions are demonstrated and supported by experimental data in nine figures and two tables.

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“…Each vial was fitted to the rod of the solid probe inlet system of a Finnigan quadrupol mass spectrometer 3100. Several spectra from about 1 -5 nmol of each probe were recorded within 3 -5 min during heating of the solid probe inlet from 100 "C to 160 "C. Chemical ionization with isobutane at 1000 p (133 x lo3 Pa) pressure as reactant gas was used exclusively for ion generation [17].…”

Section: Methodsmentioning

confidence: 99%

The Amino‐Acid Sequence of Isoinhibitor K from Snails (Helix pomatia)

Tschesche¹,

Dietl²

1975

European Journal of Biochemistry

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Performic-acid-oxidized isoinhibitor K of snails (Helix pomutiu) was subjected to argininedirected tryptic proteolysis. Six peptide fragments including one overlap peptide from limited cleavage of the Arg-3 -Pro-4 bond were purified to homogeneity. Four arginine peptides and the C-terminal peptide were sequenced by automatic Edman degradation using a special peptide program. The phenylthiohydantoins were all identified by chemical ionization mass spectrometry, except four cysteic acid residues that were identified on an amino acid analyzer after acid hydrolysis. Quantitative evaluation of the phenylthiohydantoins by chemical ionization mass spectrometry using total molecular-ion beam integration greatly facilitated sequencing. The mass spectrum of the dipeptide < GluGly revealed that the N-terminus was blocked by pyroglutamic acid.The complete amino acid sequence of isoinhibitor K was determined. An almost 50 % homology between the sequences of the snail inhibitor and the bovine trypsin-kallikrein@ inhibitor (Kunitz) became obvious. A comparison of all homologous sequences of this particular class of proteins known to date is presented. and has a striking similarity in its biochemical properties, its molecular weight and its inhibitory specificity [5,7] to the trypsinkallikrein@ inhibitor (Kunitz) of bovine organs [8]. However, its N-terminus is blocked against Edman degradation. Thus, the amino acid sequence was established by preparing and sequencing of the tryptic peptides after arginine-directed and lysine-directed tryptic cleavages of the performic-acid-oxidized inhibitor. The N-terminus was elucidated by direct mass Abbreviations. < Glu, pyroglutamic acid = pyrrolidone carboxylic acid; Tos-PheCH,CI, l-chloro-4-phenyl-3-tosylamidobutanone; Tos-LysCH,Cl, l-chloro-3-tosylamido-7-aminoheptanone; u, atomic mass units.Enzymes. Trypsin (EC 3.4.21.4); Carboxypeptidase B from porcine pancreas (EC 3.4.12.3); Carboxypeptidase C from orange lcavcs (EC 3.4.12.1).

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Studies in chemical ionization mass spectrometry

Cited by 46 publications

References 17 publications

Gas chromatography‐mass spectrometry with supersonic molecular beams

Gas chromatography‐mass spectrometry with supersonic molecular beams

A comparison of electron ionization mass spectra obtained at 70 eV, low electron energies, and with cold EI and their NIST library identification probabilities

The Amino‐Acid Sequence of Isoinhibitor K from Snails (Helix pomatia)

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