摘要:

AbstractNucleic acid extracts from 1400‐year‐old radish seeds recovered from excavations at Qasr Ibrim, Upper Egypt, have been analysed by gas chromatography/mass spectrometry and gas chromatography/mass spectrometry/mass spectrometry.tert‐Butyldimethyisilyl derivatives of the purine and pyrimidine bases were prepared, after treatment of the nucleic acid extracts with concentrated formic acid. Under electron ionization these derivatives yield prominent [M–57]+ions that were found to be of value for use in analyses employing selected‐ion monitoring and product‐ion studies. These two techniques were used in the sensitive and selective detection of nucieotide bases in crude extracts of ancient seeds. The results obtained were supported by complementary analyses of hydrolysates of ancient nucleic acids and authentic bases by means of retention time and spectral comparisons. This work demonstrates for the first time that mass spectrometry can be used in the direct chemical examination of nucleotide bases in ancient materials. This analytical approach is currently being used to address questions regarding the possible chemical (diagenetic) changes occurring in the nucleic acids of ancient biologic

ISSN:0951-4198    

DOI:10.1002/rcm.1290080702

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractTo explore the chemistry of the reactions of the cytotoxic aldehydetrans‐4‐hydroxy‐2‐nonenal (HNE) with proteins, we incubated this aldehydein vitrowith β‐lactoglobulin B, a model protein of molecular weight 18 277 Da. Direct characterization of reaction products using electrospray ionization mass spectrometry yielded spectra whose complexity suggested extensive product heterogeneity. Spectra were transformed to a true mass scale using both a conventional transform algorithm and a maximum entropy algorithm. Both transformations demonstrated the formation of aldehyde‐protein adducts containing from three to nine aldehyde molecules per molecule of protein. Maximum entropy deconvolution resolved Schiff base adducts and/or dehydration products, differing from the Michael addition adducts by 18 Da. The dominant reaction pathway, however, was Michael addition of the aldehyde to nucleophilic functional groups on the protein. The large number of Michael adducts relative to the one available cysteine requires that other amino acids, such as histidine and lysine, also be modified. The data suggest that methods for analysis of HNE that involve displacement of Schiff base groups from proteins will only recover a small fra

ISSN:0951-4198    

DOI:10.1002/rcm.1290080703

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractElectrospray ionization (ESI) in combination with Fourier‐transform mass spectrometry (FTMS) gives both highly accurate mass analysis of peptides with external calibration and high resolution for charge‐state determination of an ion from the naturally occurring isotopic peaks. Liquid chromatographic (LC) separation of peptides is important for the analysis of complex mixtures. High‐resolution, high accuracy measurement of the molecular ions of the mix of peptides has been achieved with LC/ESI‐FTMS. Examples are given to show both the reproducibility of mass accuracy over replicate analyses and to show the utility of broadband analysis of a gradient separation of peptides. The high mass accuracy and resolution of FTMS was uncompromised for the direct analysis of chromatograph

ISSN:0951-4198    

DOI:10.1002/rcm.1290080704

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractAn automated high‐performance liquid chromatography (HPLC)/mass spectrometry instrument coupled on‐line with a microdialysis probe is described for the analysis of contrast agents in biological fluids. This system is used for pharmacokinetic and structure elucidation studies of contrast agents used in X‐ray and magnetic resonance imaging investigations. Additionally an LC/MS system for the direct analysis of urine, that obviates the need for conventional sample clean‐up, is de

ISSN:0951-4198    

DOI:10.1002/rcm.1290080705

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractResonance‐enhanced multiphoton ionization has been used to detect the presence of vapour‐phase explosive‐type samples in a linear time‐of‐flight (TOF) mass spectrometer. In particular, nitrobenzene, 2‐nitrotoluene, 2,4‐dinitrotoluene, 2,4,6‐trinitrotoluene, ethylene glycol dinitrate, pentaerythritol tetranitrate (PETN), 1,3,5‐trinitro‐1,3,5‐triazacyclohexane (RDX) and SEMTEX (PETN plus RDX plus plasticizer) have been analysed at a laser wavelength of 226.3 nm corresponding to a strong resonant transition of the neutral NO molecule. TOF mass spectra have been recorded and the intensity of the NO+ion monitored as a function of temperature for comparison with the temperature dependence of the var

ISSN:0951-4198    

DOI:10.1002/rcm.1290080706

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractMethods are described for the analysis of trace levels of explosives on materials collected at the scene of real detonations. The methods exploition mobility spectrometry (IMS) to confirm and enhance the results obtained by high performance liquid chromatography with an ultraviolet detector (HPLC‐UV). Solvent‐extracted samples contain many interfering substances and are cleaned up by solid‐phase extraction (SPE) prior to HPLC fractionation. Explosive‐containing HPLC fractions are analysed by IMS after removal of solvent by vacuum centrifuge. IMS detection limits for explosives, typically a few hundreds of picograms, are at least an order of magnitude lower than those for UV detection. SPE and HPLC fractionation also removes interfering substances that can otherwise suppress IMS detection. Explosives discussed are di‐ and trinitrotoluene, ethylene glycol dinitrate, nitroglycerin, pentaerythritol tetranitrate, hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine, octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetraazine, andN‐methy

ISSN:0951-4198    

DOI:10.1002/rcm.1290080707

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractThe methyleneketene radical anion is formed from Me3SiCOCHCH2. Deprotonation of this neutral by NH 2−yields Me3SiCOC̄CH2which then decomposes by loss of Me3Si·to yield CH2CCO−·. The identity of the product radical anion is determined by its charge‐reversal (positiv

ISSN:0951-4198    

DOI:10.1002/rcm.1290080708

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractThe electron ionization mass spectra of 19 tricyclic fused pyrimidinone derivatives were studied. The molecular ions of almost all of these compounds were very stable and formed the base peaks of the spectra. The degree of saturation, the size and substitution of rings A and C (pyrimidinone itself is ring B) were the dominant factors affecting the type of fragmentation which, however, in general was quite simple.

ISSN:0951-4198    

DOI:10.1002/rcm.1290080709

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractA new strategy has been developed for the determination of the amino acid sequence of apamin, a two disulfide‐bond neurotoxic oligopeptide. Relative molecular mass up to about 2000 was determined using electrospray mass spectrometry. This technique shows that three basic amino acid residues are present in apamin. A hydrophobic tryptic digest fragment was sequenced using fast‐atom bombardment combined with tandem mass spectrometry. But the full sequence has been directly observed using a tandem mass spectrometer: the daughter‐ion mass spectrum of protonated molecules of dithiothreitol‐reduced apamin gives the s

ISSN:0951-4198    

DOI:10.1002/rcm.1290080710

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractThe enhanced performance of electro‐osmotically driven high performance liquid chromatography (HPLC) using reversed‐phase packed capillaries has been evaluated for coupling to mass spectrometers, as an alternative to both conventional pressure‐driven elution, and to micellar electrokinetic capillary chromatography for the separation of neutral analytes. An off‐line comparison of electro‐osmotically driven versus pressure driven chromatography for the separation of an aromatic mixture shows the superiority of the method over conventional HPLC. Coupling of the technique with continuous‐flow fast‐atom bombardment for the analysis of a steroid mixture

ISSN:0951-4198    

DOI:10.1002/rcm.1290080711

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY