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131.
Russell SC Czerwieniec G Lebrilla C Tobias H Fergenson DP Steele P Pitesky M Horn J Srivastava A Frank M Gard EE 《Journal of the American Society for Mass Spectrometry》2004,15(6):900-909
The appearance of informative signals in the mass spectra of laser-ablated bio-aerosol particles depends on the effective ionization probabilities (EIP) of individual components during the laser ionization process. This study investigates how bio-aerosol chemical composition governs the EIP values of specific components and the overall features of the spectra from the bio-aerosol mass spectrometry (BAMS). EIP values were determined for a series of amino acid, dipicolinic acid, and peptide aerosol particles to determine what chemical features aid in ionization. The spectra of individual amino acids and dipicolinic acid, as well as mixtures, were examined for extent of fragmentation and the presence of molecular ion dimers, which are indicative of ionization conditions. Standard mixtures yielded information with respect to the significance of secondary ion plume reactions on observed spectra. A greater understanding of how these parameters affect EIP and spectra characteristics of bio-aerosols will aid in the intelligent selection of viable future biomarkers for the identification of bio-terrorism agents. 相似文献
132.
Mineral and short-chain carboxylic acid vapours and NO(x) gases were reacted with cyclohexene oxide (1,2-epoxycyclohexane) to quantitatively produce specific, thermally stable cyclohexyl derivatives. Subsequent analysis of these derivatives by gas chromatography with mass spectroscopy and flame ionisation detection afforded a multi analyte method for the assay of these gaseous acidic atmospheric species. Derivatisation was found to be quantitative for the derivatives tested and the method highly sensitive (to 0.3 mg/m3 for a 30 l sample), accurate, precise and free from apparent interferences. The technique has been applied to "acid stack gases" and a number of other acid rich atmospheres and the results obtained show good agreement with the single analyte wet chemical determinations indicating that the approach has considerable potential as a routine analytical method for measuring such atmospheric pollutants. The high specificity of the reaction mechanism and its potential for the analysis of analyte mixtures is illustrated in the assay of nitric acid and its acid anhydride, dinitrogen pentoxide. 相似文献
133.
Glass capillaries coated with Chirasil-Val, a chirally functionalised polysiloxane, are capable in principle of resolving all protein amino-acid enantiomers in a single run and within a short analysis time, thus allowing for example the quantitative amino acid determination by enantiomer labelling. The elution characteristics of the individual amino acids however are also dependent upon the chemical nature of the capillary wall surface, and a surface pretreatment is found to be necessary if all protein amino acids are to be analysed. Of the various methods of pretreatment tested, etching of borosilicate glass with gaseous HCl followed by deposition of colloidal silicic acid is considered to be the most suitable. 相似文献
134.
Peter C. Burgers J. L. Holmes F. P. Lossing Frank R. Povel Johan K. Terlouw 《Journal of mass spectrometry : JMS》1983,18(8):335-339
The structures of the m/z 87, [C4H7O2]+, ions generated by dissociative ionization of CH3CGXCOOCH3 and XCH2CH2COOCH3 (X = CH3, Cl, Br, and I) have been investigated via their unimolecular and collisionally activated fragmentations and by apperance energy measurements. For both precursors loss of X = CH3 produced, via H atom transfer, ions of structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH_2 = CH}\mathop {\rm C}\limits^{\rm + } \left({{\rm OH}} \right){\rm OCH}_{\rm 3} $\end{document} (a), ΔHf = 386 kj mol?1. In marked contrast, loss of I˙ from ionized CH3CHICOOCH3 and ICH2CH2COOCH3 proceeded without rearrangement to yield respectively ions of structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH_3}\mathop {\rm C}\limits^{\rm + } {{\rm HCOOCH_3}} $\end{document} (b), ΔHf = 480 kJ mol?1 and (c), ΔHf = 450 kJ mol?1. These different fragmentation behaviours are explained via photoelectron spectra which show that the formal charge site in the precursor ion is at the carbonyl oxygen when X = CH3 but at the halogen atom when X = I. The precursor molecules X = Cl and Br display both of the above characteristics, CH3CHXCOOCH3 yielding mixtures of a and b and XCH2CH2COOCH3 producing a and c ions. 相似文献
135.
[reaction: see text] During the course of drug metabolism studies, a major metabolite of compound 1 was detected in rhesus monkeys and assigned structure 4. The intriguing biotransformation of 1 leading to 4 was confirmed by a 19-step total synthesis starting from resorcinol (11), the key feature of which was the construction of the oxygen bridge utilizing a phenolic oxidation and trapping sequence. In addition, the synthesis of a related metabolite (5) is described. 相似文献
136.
Quinazoline, acid chlorides, and trimethylsilyl cyanide have been converted to mono-Reissert compounds at the 3,4-position of the quinazoline system. Various reactions of these quinazoline Reissert compounds are reported. 相似文献
137.
Surowiec I Baena JR Frank J Laurell T Nilsson J Trojanowicz M Lendl B 《Journal of chromatography. A》2005,1080(2):132-139
A flow-through microdispenser has been coupled to a micro HPLC separation system and used as a solvent elimination interface for Fourier transform infrared (FTIR) and Raman spectroscopic detection of the separated compounds. Using the microdispenser picoliter sized droplets can be generated and deposited on an appropriate target placed on a computerized x, y-stage. Evaporation of volatile solvent and buffer is rapid and allows analysis of the obtained dry deposits by various techniques. Due to the destruction free character of Raman and FTIR spectroscopy they can be applied sequentially to interrogate the same deposit. In the reported application five phenolic acids typically present in wine have been separated on a C-18 column technique using a mixture of water, methanol and acetic acid as mobile phase. For spectrum acquisition infrared and Raman microscopes have been used. The spectra recorded from the dried deposits of the separated compounds agreed well with the reference spectra of corresponding components. 相似文献
138.
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