摘要:

AbstractOak and chestnut cask staves were planed to a depth of one centimeter, collecting a sample every millimeter. The samples were ground and subjected to pyrolysis/gas chromatography/mass spectrometry in order to determine their composition. Thirty‐six compounds were identified, including a series of typical lignin phenolics commonly considered responsible for wine taste. All ions found in a previous pyrolysis/mass spectrometry study of oak wood and related to good quality whisky were confirmed in the mass spectra of the pyrolysis fragments specific for polysaccharides and lignin recorded in the present work. Compared to chestnut wood, oak wood showed significantly higher lignin and syringyl unit content and less variability as to lignin composition with dept

ISSN:0951-4198    

DOI:10.1002/rcm.1290091402

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe behavior of peptides containing multiple tyrosine‐O‐sulfates in liquid secondary‐ion mass spectrometry (LSIMS) has been investigated. In the positive‐ion spectra of the peptides containing two tyrosine‐O‐sulfates, Cionin and CCK‐associated C‐terminal nonapeptide (CAP‐9), the completely desulfated [M+H−2SO3]+ions formed the base peaks, accompanying the significantly less‐intense [M+H]+and [M+H−SO3]+ions. In the negative‐ion spectra of these peptides, the [M−H]−and [M−H−SO3]−ions gave prominent peaks with significantly weaker [M−H−2SO3]−ions. In the case of a peptide containing three tyrosine‐O‐sulfates, [Tyr(SO3H)1]CAP‐9, the completely desulfated [M+H−3SO3]+ion again formed the base peak in the positive‐ion spectrum. On the other hand, the sulfated tyrosine‐containing [M+H]+, [M+H−SO3]+, and [M+H−2SO3]+ions were of negligible abundance compared to the spectra of peptides containing two tyrosine‐O‐sulfates. We observed an intriguing ‘ladder fragmentation pattern’ in the negative‐ion spectrum of this triply‐sulfated peptide. The ladder consisted of the [M−H]−, [M−H−SO3]−, and [M−H−2SO3]−ions, but without the completely desulfated [M−H−3SO3]−ion. These characteristic fragmentation patterns of sulfated tyrosine‐containing peptides were considered to bear a close correlation with the inherent acid‐lability of a tyrosine‐O‐sulfate in solution. A possible mechanism has been proposed

ISSN:0951-4198    

DOI:10.1002/rcm.1290091403

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractCollisionally‐activated dissociation (CAD) studies of linear peptides were performed using matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. Four different gases, viz. helium, nitrogen, argon and xenon, were introduced into a gas cell, installed close to the ion source of TOF mass spectrometer, to obtain high‐energy CAD information. The CAD spectral patterns for the linear peptides obtained using the four gases were almost the same as each other. The fragments characteristically obtained in conventional high‐energy CAD using tandem mass spectrometry were observed also in these spectra. A difference between CAD spectra and post‐source decay product‐ion spectra has be

ISSN:0951-4198    

DOI:10.1002/rcm.1290091404

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe electron impact mass spectra of some 1‐(2‐furyl)‐ and 1‐(2‐thienyl)‐2‐(2‐benzothiazolyl) ethenes have been recorded and the identity of various ions in the mass spectra established. The compounds examined (1–10) exhibit two main fragmentation routes. On one hand, fragmentation of the furan and thiophene nuclei and the formation of cyclopropenylethyne cations with very significant abundance and on the other hand, fragmentation of the benzothiazole nuclei on characteristic pathways. Compounds 6–10 also show two additional f

ISSN:0951-4198    

DOI:10.1002/rcm.1290091405

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractBy positioning the capillary of the ion spray parallel to the ion sampling orifice, several advantages have been found compared to the conventional perpendicular ion spray, e.g., higher sensitivity, stable operation, practically no contamination of the ion sampling orifice, and higher liquid flow rates up to 4 mL/min. This is due to the fact that while the charged fine liquid droplets are deflected towards the ion sampling orifice, the larger liquid droplets with lower charge density are entrained in the nebulizer gas jet and they are carried away outside the ion sampling system. With higher liquid flow rates (e.g. ⩾500 μL/min), the start of corona discharge does not result in a drastic decrease in the signal intensities of ions originating from sample solution. In electrospray experiments, it has also been found that the parallel spray gives better performance than the perpendicular o

ISSN:0951-4198    

DOI:10.1002/rcm.1290091406

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractA time‐of‐flight mass spectrometer has been developed using a reflectron in which the voltages placed on the lens elements correspond to a function describing the arc of a circle. Thiscurved‐field reflectronenables acquisition of focused product‐ion mass spectra at a single reflectron voltage. In this paper, we present results from this instrument for the amino acid sequencing of several peptides and describe the method of mass cali

ISSN:0951-4198    

DOI:10.1002/rcm.1290091407

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractPositive/negative chemical ionization (PI/NI CI) and liquid secondary ion mass spectrometry (LSIMS) of ten derivatives of dicyclopentadienyltitanium (IV) dichloride were investigated. The major ions detected were M + NHU4, M − CI]+, [M − 2Cl]+, [M − R1CpR3]+and [M − R2CpR4]+in PICI (ammonia) mass spectra, M−, [M + CI]−, [M − CI]−, [M + CI − R1CpR3]+and [M + CI − R1CpR3]+in NICI (ammonia) mass spectra, and [M − CI]+, [M − 2CI]+, [M − 2CI + (NBA − H)]+(where NBA =m‐nitrobenzyl alcohol), [M − R1CpR3]+, [M − R2CpR4+, [M − R1CpR3− HCI]+and [M − R2CpR4− HCI]+(where R1CpR3and R2CpR4are both mixed alkyl‐aryl substituted cyclopentadienyl groups) in LSIMS. Although the mass spectrometric behaviours are quite different due to the different ionization mode, adduct ions were observed in all mass spectra and molecular ions were only observed in NICI mass spectra. The cleavage pathways were confi

ISSN:0951-4198    

DOI:10.1002/rcm.1290091408

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThis work concerns a new high‐pressure quadrupole collision cell, designed for tripie‐quadrupole mass spectrometers. This new collision cell operates at pressures up to 10 mTorr, an order of magnitude higher than conventional cells of this type. Previous investigations have concentrated upon the significant increases in transmission efficiency and in resolving power for fragment ions which result from the use of this new design. The present work reports an investigation into the nature of the dissociation reactions which can be induced by collisions in this high‐pressure cell. Charge‐site‐remote fragmentations of a simple precursor ion were chosen as a test case, and were found to be observable at laboratory collision energies lower by a factor of 4–5 than those found previously to be necessary when using conventional low‐pressure quadrupole collision cells. It was also shown that the charge‐site‐remote reactions were accompanied by the mixed‐site‐fragmentation reactions described by Tuinman and Cook (J. Am. Soc. Mass Spectrom). Vol. 1, p. 85 (1989). Ionization of collision gas was observed in the case of xenon. Efforts to observe charge‐site‐remote fragmentations of peptide ions were marginally successful. Highly basic peptides, which have been problematic for sequencing by low‐energy tandem mass spectrometry, did not yield useful fragment‐ion spectra in the new cell. The fragmentation behaviour of protonated Leu‐enkephalin, for which fragmentation pathways have been thoroughly studied previously, suggested that the observed spectra reflected integration of the fragmentation kinetics over a considerably longer time, thus involving many more reaction steps. These combined observations are considered in terms of a qualitative model based on a rapid decrease of ion kinetic energy during passage through the cell, with much longer residence times than fo

ISSN:0951-4198    

DOI:10.1002/rcm.1290091409

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe mass spectrometric behaviour of two pairs of fluorinated vinyl‐ and allyl‐ethers and thioethers has been studied in detail with the aid of metastable ion data and accurate mass measurements. Clear differences have been observed between the two sets of compounds; while for the ethers the McLafferty rearrangement with ethylene loss represents a highly favoured decomposition route, for the thioethers the loss of the ethyl radical is preferred. Some decomposition routes, common to all the compounds examined, suggest the presence of hydrogen atom bridging between carbon and fluorine atoms. Theoretical calculations have shown that such aquasiCHF structure is already present in the neutral molecule in its groun

ISSN:0951-4198    

DOI:10.1002/rcm.1290091410

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractA method has been developed for the rapid and sensitive mass spectrometric characterization of peptides. The approach usesbioreactivemass spectrometer probe tips, incorporating covalently bound enzymes, which are capable of modifying biomolecules for analytical purposes. In the demonstrated cases, enzymatic proteolysis is initiated upon application of analyte to the probe tips, time is allowed for digestion, and the products are analyzed using matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. The probe tips have been used for proteolytic mapping and partial sequence determination of picomole quantities of peptide. Analysis times were approximately 30 min. Two methods of database search were utilized. The first used limited peptide sequence information and parent molecular weight, while the second used exclusively the molecular weights of a number of endoproteolytic fragments. A simple method of comparing the match of experimental data for a tryptic digest with the results of a search is desc

ISSN:0951-4198    

DOI:10.1002/rcm.1290091411

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY