摘要:

AbstractThe mass spectrometric behaviour of a series of azasqualenes and azasqualanes has been studied by two different instruments, a double focusing machine and an ion‐trap mass spectrometer (ITMS). The high abundances of fragmentation products obtained using the former indicate that with ITMS, processes additional to electron ionization must be present, leading to molecular species with lower internal energy content

ISSN:0951-4198    

DOI:10.1002/rcm.1290080112

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractLiquid secondary‐ion mass spectrometry (LSIMS) experiments were performed on a series of model quaternary ammonium chlorides [M Q+Cl−] in order to develop a strategy, via an understanding of cluster‐ion formation, for recognition of quarternary ammonium structures. Model structures contained a single quaternary site and various other structural features (for example, conjugated quaternary systems and carboxylic acid groups), using amine hydrochlorides as controls. Cluster ions were examined with both positive‐ and negative‐ion LSIMS, using a range of matrix modifiers. Precursor scans, or ‘molecular weight confirmation scans’, of M Q+(the charged molecular ion of quaternary ammonium compounds) and [M+H]+ions were used to assist in the observation of cluster ions and to unambiguously demonstrate precursor/product relationships. Positive‐ion experiments typically showed dimeric clusters of [2MQ+ A]+(A=anion) and [2MQ−H]+ions, while negative ion experiments produced [MQ+ 2A]−ions. Observation of these cluster ions coupled with the lack of an [M−H]−ion are a distinguishing feature of quaternary amines. Additional cluster ions were targeted for distinguishing between protonated amines and quaternary amonium compounds containing a carboxylic acid group. A strategy for recognizing and distinguishing quaternary ammonium structures using LSIMS is proposed, and some initial experiments with thermospray and

ISSN:0951-4198    

DOI:10.1002/rcm.1290080113

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractA new mass spectrometry technique using an inductively coupled plasma (ICP) ionization source and an ion‐trap mass spectrometer (ITMS) detector is described and evaluated for elemental and isotopic analysis. Initial results obtained with the ICP‐ITMS technique include sub‐ppb detection of bare ions for, most elements, complete destruction of typical polyatomic matrix ions (e.g., CIO+, ArO+, and ArCl+), and effective neutralization of strong Ar+ion currents. The latter effects allow observation of clearer mass spectra atm/z<80 and potentially improved detection of ‘problem’ elements in ICP‐MS (e.g., K, Ca, V, Fe, As, and Se). Formation of poly‐oxide and ‐hydroxide ions of metals with high oxide bond strengths were observed and require system modificatio

ISSN:0951-4198    

DOI:10.1002/rcm.1290080114

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractA termination synthesis approach has been developed to encode each resin bead in support‐bound combinatorial peptide libraries with the information needed to establish the sequence of the full‐length products also contained on the beads. Matrix‐assisted laser desorption ionization mass spectrometry was then used to rapidly read the appropriate sequences. In addition to rapid peptide sequencing, the technique allows direct assessment of the quality of the synthetic library, since deletion peptides, side‐reaction products and incomplete‐deprotection products are readily observed. An anti‐gp120 monoclonal antibody was screened against a hexapeptide library, and eight active peptides were isolated. Six of the eight peptides were shown to possess the exact recognition sequence for t

ISSN:0951-4198    

DOI:10.1002/rcm.1290080115

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractThermospray mass spectrometry was used to analyze fumonisin B1(FB1) from two corn samples that were known to contain fumonisins, and from a FB1‐spiked meat sample. The mass spectrometer was operated in the negative‐ion discharge‐on, filament‐off, mode with the fragmentor set at 200 V. Selected‐ion monitoring (SIM) was used for quantitative analysis. The mobile phase was CH3CN (containing 1% CICH2CN, v/v)+0.1M ammonium acetate, pH 3.65 (65:35, v/v). Quantitative analysis was done by integrating the peak areas traced by ion currents of 5 selected ions in SIM, and by the method of standard additions. Responses to the selected ions were linear within the range of 2‐200 ng. Fumonisins were easily identified in the corn and muscle tissue matrices without any apparent matrix interferences and were detectable down to 0.1 μ/mL (2

ISSN:0951-4198    

DOI:10.1002/rcm.1290080116

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractThe kinetics of the unimolecular dissociations of proton‐bound dimers produced by fast‐atom bombardment from nucleosides and reference amines enables the evaluation of the proton affinities (PA) of ribonucleosides. The PAs of cytosine, guanosine, adenosine, uridine and deoxyuridine have been thus determined. These values and those already available for the corresponding DNA homologues allow the evaluation of the effect of the hydroxyl group in position 2′ of the sugar moiety, which lowers the PAs of RNA nucleosides by 0.6–1 kcal/mol, and of the methyl group in position 5 of the thymine ring which enhances the basicity of deoxythymidine over deoxyuridine by 0.6 k

ISSN:0951-4198    

DOI:10.1002/rcm.1290080117

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractA rapid method for identifying and characterizing sites of phosphorylation of peptides and proteins is described. High‐performance capillary liquid chromatography (HPLC) coupled with electrospray ionization mass spectrometry (ESI‐MS) is used to distinguish non‐phosphorylated and phosphorylated peptides originating from mixtures as complex as enzyme digests. The method relies on the ability to produce a fragment ion characteristic and unique to phosphopeptides (m/z79, PO3−) by stepping the orifice potential of the mass spectrometer as a function of mass. At lowm/zvalues, a high orifice potential is applied to induce extensive fragmentation of the peptide, leading to the formation of them/z79 phosphate‐derived ion. This method is analogous to that described by Carret al.for the identification of glycopeptides from enzymatic digestion of glycoproteins (S.A. Carr, M. J. Huddleston, M. F. Bean,Protein Science2, 183 (1993)). The method was first evaluated and validated for a mixture of non‐, mono‐ and di‐phosphorylated synthetic peptides. Both mono‐ and di‐phophorylated peptides were found to generate fragment ions characteristic of PO3−whereas the non‐phosphorylated peptide did not. Application of the method was extended to identifying phosphopeptides generated from an endoprotease Lys‐C digestion of β‐casein. Both the expected mono‐ and tetra‐phosphorylated Lys‐C peptides were observed and identified rapidly in the LC/SEI‐MS analysis. The procedure was used additionally to identify the site(s) of phosphorylation of the cytosolic non

ISSN:0951-4198    

DOI:10.1002/rcm.1290080118

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractStructures of the trifunctional crosslink molecules, pyridinoline, deoxypyridinoline and glucosylgalactosyl‐pyridinoline, have been characterized by positive‐ion liquid secondary‐ion mass spectrometry (LSIMS) and collision‐induced dissociation with scanning‐array four‐sector tandem mass spectrometry. It has been found that: (i) the naturally occurring cations (Cat+) are readily desorbed by positive‐ion LSIMS utilizing glycerol + thioglycerol (1:1) as liquid matrix and dominate the spectra, facilitating accurate mass measurement; (ii) changing the matrix to 3‐nitrobenzyl alcohol leaves little evidence of the cation, and (iii) collision‐induced dissociation of the cations (Cat+) of pyridinoline, deoxypyridinoline and glucosylgalatosyl‐pyridinoline gives a wealth of fragmentation for structure elucidation. These fundamental studies of tandem mass spectra of the known trifunctional crosslink molecules provided valuable structure‐related information, which help in the identification of the tissue‐specific peptides containing these crosslinks. Artefact ions in these tandem mass spectra

ISSN:0951-4198    

DOI:10.1002/rcm.1290080119

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractCapillary column supercritical fluid chromatography (SCF) was combined with atmospheric pressure chemical ionization (APCI) mass spectrometry through a heated pneumatic‐nebulizer interface, originally developed for liquid chromatography/mass spectrometry (LC/MS), and subsequently modified for use with supercritical fluid chromatography/mass spectrometry (SFC/MS). A high pressure syringe pump was used to pass SFC‐grade carbon dioxide, used as the mobile phase, through a capillary SFC column which was contained in an oven, maintained at 100°C. The eluent passed through the heated pneumatic‐nebulizer interface into the ionization region of the mass spectrometer with the aid of the flow of nebulizing gas. The system was optimized using benz[a]anthracene, and then applied to analyze a standard mixture of polycyclic aromatic compounds (PACs) as well as complex mixtures of PACs obtained by the fractionation of a pond sediment contaminated by coke‐oven residues. A detection limit of 40 pg was established for

ISSN:0951-4198    

DOI:10.1002/rcm.1290080120

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractThe mass spectrometric behaviour of ten variously substituted mono‐ and bis‐salicylaldimine derivatives has been studied by fast‐atom bombardment and metastable‐ion studies. In general, well detectable protonated molecules are present and fragmentation processes mainly related to aldimine chain cleavages are evidenced. Interesting cyclization reactions leading to particularly stable product ions are di

ISSN:0951-4198    

DOI:10.1002/rcm.1290080121

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY