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  • 1
    Electronic Resource
    Electronic Resource
    Diamine reagents in thermospray mass spectrometry (1992)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 21 (1992), S. 125-132 
    Details
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Determination of the molecular weight for an unknown by thermospray liquid chromatographic/mass spectrometric analysis using ammonium acetate mobile phase can be both confusing and misleading. This is due to the uncertainty of whether an ion is either a protonated species or an ammonium adduct or both. Deuterium oxide and ammonium acetate buffers have been used to elucidate molecular species of unknown compounds with some success. We have investigated an alternative method which utilizes diamine reagents. This method simplifies the identification of unknown molecular species in an inexpensive manner. Diamines form adduct ions readily with many substances. A comparison of spectra obtained for an unknown using ammonium acetate or diaminoethane in separate analyses is useful for identifying molecular species. Using ammonium acetate as a mobile phase, a molecule is often detected as a protonated molecular species. However, using diaminoethane mobile phase, this same molecule is most often detected as a diaminoethane adduct. Comparison of each spectrum reveals a mass difference of 60 for a molecule detected as a protonated species and a diaminoethane adduct. In addition, a mass difference of 43 will be obtained in a similar spectral comparison if a molecule forms ammonium adducts using ammonium acetate mobile phase and diaminoethane adducts using diaminoethane. An analysis of an unknown substance with several molecular species is presented as an example of the utility of diamine reagents in thermospray mass spectrometry. By observing mass spectral differences, molecular species can be identified as either a protonated ion or an adduct ion.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bms.1200210303
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  • 2
    Electronic Resource
    Electronic Resource
    Applications of deuterium labeling in the study of the in vitro conversion of Δ1-pyrroline to 4-aminobutanoic acid and 2-pyrrolidinone (1980)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 7 (1980), S. 525-528 
    Details
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Δ1-Pyrroline is a putrescine metabolite that is biotransformed by rabbit liver preparations to 4-aminobutanoic acid and its lactam, 2-pyrrolidinone. Analysis of dilute aqueous solutions of Δ1-pyrroline by proton nuclear magnetic resonance indicated that the predominating species in the liver incubation preparations was Δ1-pyrroline monomer, although other species, such as 4-aminobutyraldehyde and Δ1-pyrroline trimer, may exist in equilibrium with the monomer. [2H12]-Δ1-Pyrroline trimer was synthesized from [2H5]pyrrolidine by conversion to the N-chloro derivative followed by dehydrohalogenation. 4-Aminobutanoic acid was measured by a gas chromatographic mass spectrometric assay after derivatization with dimethylformamide dimethyl acetal. The 4-aminobutanoic acid homologue, 5-aminovaleric acid, served as internal standard. 2-Pyrrolidinone was hydrolyzed and measured as 4-aminobutanoic acid. A comparison of the amounts of product formed following incubation of labeled and unlabeled Δ1-pyrroline indicated a significant isotope effect in the formation of 2-pyrrolidinone. The influence of the label was much less on 4-aminobutanoic acid production. The results suggest that there are two separate pathways involved in the reaction.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bms.1200071114
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  • 3
    Electronic Resource
    Electronic Resource
    Supercritical fluid chromatography/chemical ionization/mass spectrometry of some anticancer drugs in a thermospray ion source (1990)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 19 (1990), S. 348-352 
    Details
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A packed-column supercritical-fluid chromatograph was interfaced with a mass spectrometer via a modification of a thermospray probe. This modification allowed a capillary restrictor for the supercritical fluid (CO2) and reagent gas for chemical ionization to be introduced directly into a thermospray source. Chemical ionization conditions were observed when either the filament or discharge electrode was used and the source pressure was above 0.5 torr. The discharge electrode produced more efficient ionization, resulting in approximately a tenfold larger signal than that observed in the filament mode. The usefulness of this instrumentation was demonstrated on several anticancer drugs. Methanol positive ion chemical ionization (PICI) spectra were recorded for cyclophosphamide, diaziquone, mitomycin C and thiotepa. Methane PICI spectra of thiotepa were obtained in the absence of methanol as a mobile-phase modifier. A 50 ng on-column injection of diaziquone produced approximately a 6:1 signal to noise ratio in the scanning mode.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bms.1200190604
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  • 4
    Electronic Resource
    Electronic Resource
    Mass spectrometry of thermally unstable molecules. Evaluation of ionization techniques using glutamine as a reference compound (1985)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 12 (1985), S. 699-703 
    Details
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A limiting factor in the application of mass spectrometry to biochemically important molecules has been the inability to analyze compounds without inducing thermal decomposition. Glutamine, which readily cyclizes to 2-pyrrolidone-5-carboxylic acid with loss of ammonia, is one of the more difficult of these non-volatile, thermolabile biomolecules to determine. Using a heated, direct probe, no molecular ion for glutamine was observed with electron impact ionization. A protonated molecular ion was detected with direct probe chemical ionization and thermospray. In both cases, the major ion formed was derived from the thermolysis product, 2-pyrrolidone-5-carboxylic acid. Analysis by fast atom bombardment and 252Cf plasma desorption mass spectrometry yielded a molecular ion as base peak with a small ion from the 2-pyrrolidone-5-carboxylic acid. Ion evaporation produced only the molecular cations, and collisionally activated dissociation demonstrated that glutamine does not cyclize appreciably once protonated. These results suggest that glutamine can be used as a reference compound when analysis requires the optimization of conditions to produce a molecular ion. Furthermore, the relative intensity of the pyrolytic products, 2-pyrrolidone-5-carboxylic acid derived molecules, divided by the relative intensity of the molecular ions of glutamine provides a numerical evaluation of ionization conditions.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bms.1200121205
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  • 5
    Electronic Resource
    Electronic Resource
    Formation of an unusual MH- ion in the methane negative-ion chemical ionization mass spectra of chlorprothixene and aromatic sulfur compounds (1989)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 24 (1989), S. 385-390 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The methane negative-ion chemical ionization (NCI) mass spectrum of chlorprothixene shows an unusual MH- ion. This ion can be accounted for by electron capture followed by H· transfer from the reagent gas. The most probable site of electron attachment was concluded to be related to the sulfur atom of the thioxanthene ring based on the observation of analogous ions for structurally related compounds, all containing a heterocyclic sulfur. The MH- ion observed with methane as the reagent gas was shifted to MD- when tetradeuteromethane was used in place of methane. The ratio of [M — H]- to MH- did not change with emission current suggesting that the process is independent of the radical concentration in the CI plasma. Consistent with this observation is the lack of CH3· or C2H5· adduct ions in the NCI mass spectrum and the fact that gold-plating the ion source did not decrease the proportion of MH-. Also, this mechanism is consistent with thermochemical considerations of reactions of a phenyl radical with various alkanes and observations of ions formed by methane NCI from model compounds. Therefore, unlike other MH- ions observed in methane NCI mass spectra, the mechanism of formation does not appear to involve a hydrogen radical addition followed by electron capture.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210240605
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  • 6
    Electronic Resource
    Electronic Resource
    Detection of the in vivo conversion of 2-pyrrolidinone to γ-aminobutyric acid in mouse brain† GABA = γ-aminobutyric acid; AVA = 5-aminovaleric acid; DMF-DMA = N,N-dimethylformamide dimethyl acetal (1979)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 6 (1979), S. 23-26 
    Details
    ISSN: 0306-042X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Labeled γ-aminobutyric acid was detected in mouse brain following intravenous injections of deuterium labeled 2-pyrrolidinone. [2H6]Pyrrolidinone was prepared by the reduction of [2H4]succinimide with lithium aluminum deuteride. Quantification was accomplished by a gas chromatography mass spectrometry assay method. γ-Aminobutyric acid and internal standard, 5-aminovaleric acid, were converted to volatile derivatives by treatment with N,N-dimethylformamide dimethyl acetal. Quantitative estimates were derived from peak area measurements obtained from monitoring the parent ions of the γ-aminobutyric acid and internal standard derivatives by repetitive scanning during the GC run. The conversion of pyrrolidinone to γ-aminobutyric acid may provide a method for labeling central γ-aminobutyric acid pools.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bms.1200060106
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