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1.
Using nitrobenzene as an example, various ways in which a contemporary mass spectrometer can be utilized to yield a wealth of information about the compound studied are reviewed. Applying a variety of different techniques and procedures, in addition to the conventional low resolution mass spectrum, the following nitrobenzene spectra have been obtained: collision induced dissociation mass spectrum, mass analysed ion kinetic energy spectra, collision induced dissociation mass analysed ion kinetic energy spectra, spectra obtained at constant B/E, spectra obtained at constant B2/E, high voltage scans of metastable ion fragmentation processes, consecutive fragmentations in different field free regions, charge exchange mass spectra, charge stripping mass spectra, doubly charged ion mass spectra, chemical ionization mass spectra, negative ion mass spectra, negative ion mass analysed ion kinetic energy spectra, negative ion mass analysed ion kinetic energy collision induced dissociation spectra, charge inversion spectra, etc. The complementary types of information available from the above studies are discussed to show the unique versatility of mass spectrometry as a technique for the examination of organic compounds.  相似文献   

2.
Candida albicans is the most frequent yeast involved in human infections. Its population structure can be divided into several genetic clades, some of which have been associated with antifungal susceptibility. Therefore, detecting and monitoring fungal clones in a routine laboratory setting would be a major epidemiological advance. Matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) mass spectra results are now widely used as bar codes to identify microorganisms in clinical microbiology laboratories. This study aimed at testing MALDI‐TOF mass spectra bar codes to identify clades among a set of C. albicans isolates. Accordingly, 102 clinical strains were genotyped using 10 microsatellite markers and analyzed via MALDI‐TOF mass spectrometry. The mass spectra were compared with a reference spectral library including 33 well‐characterized collection strains, using a MicroflexTM system and BiotyperTM software, to test the capacity of the spectrum of a given isolate to match with the reference mass spectrum of an isolate from the same genetic clade. Despite high confidence species identification, the spectra failed to significantly match with the corresponding clade (p = 0.74). This was confirmed with the MALDI‐TOF spectra similarity dendrogram, in which the strains were dispersed irrespective of their genetic clade. Various attempts to improve intra‐clade spectra recognition were unsuccessful. In conclusion, MALDI‐TOF mass spectra bar code analysis failed to reliably recognize genetically related C. albicans isolates. Further studies are warranted to develop alternative MALDI‐TOF mass spectra analytical approaches to identify and monitor C. albicans clades in the routine clinical laboratory. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

3.
The effect of electrospray ionization (ESI) conditions on low-energy tandem mass spectra of peptides in the relative molecular mass range 400–1200 was examined. For singly charged peptide ions the source skimmer potential (which determines the degree of acceleration of the ions through the intermediate pressure region in the source) can strongly influence the extent of fragmentation observed in tandem mass spectra, especially at low collision energies. For each peptide there is an optimum skimmer potential which represents a balance between generating ions with sufficient internal energy for subsequent tandem mass spectrometric experiments and inducing the onset of other processes such as source fragmentation. The fragmentation which can be achieved in tandem mass spectra with high skimmer potentials differs from ESI source fragmentation for the same peptides. We have found that fragmentation in ESI mass spectra depends both on skimmer potential and on solvent pH, presumably because the latter determines the proportion of doubly charged species generated from a given peptide. Low-energy tandem mass spectra of peptides following ESI are equally as sensitive to peptide structure and the type of adduct studied (e.g. [M + H]+ vs. [M + NH4]+) as tandem mass spectra obtained following older ionization methods such as fast atom bombardment.  相似文献   

4.
The electron impact mass spectra of tert-butyldimethylsilyl-, cyclo-tetramethylene-tert-butylsilyl and cyclo-tetramethylene-isopropylsilyl- ether derivatives of ribo- and 2′-deoxyribonucleosides are described in detail. The interpretation of fragmentation pathways of full and mixed derivatives was aided by metastable ion decomposition studies, precise mass and deuterium labelling measurements, and spectra of mixed derivatives containing the ‘passive’ (in these spectra) trimethylsilyl group. The sterically crowded silyl groups have a powerful fragmentation directing effect. Elimination of a bulky radical, R˙ (tert-butyl or isopropyl), from the molecular ion produces the siliconium ion [M? R]+, which is the precursor for most of the other prominent ions in the spectra. These arise from ‘siliconium ion rearrangements’ resulting from the interaction of the positively charged siliconium ion center with electron dense regions (i.e. oxygens) in the molecule, to form cyclic silyloxonium ions which subsequently decompose. Since the interacting oxygen and silicon must be sterically accessible, the fragment ion types and their abundances are very dependent upon structure. Consequently, [M? R]+ ions formed from 2′, 3′ or 5′-O-silyl groups give rise to different sets of daughter ions which, for the most part, are not found, or have very low abundances, in the mass spectra of underivatized or trimethylsilylated nucleosides. Detailed information on sugar and base moieties and isomeric substitution is readily obtained.  相似文献   

5.
The mass spectra of a series of N, N′-disubstituted bispidinc derivatives have been investigated, and salient features analogous to those seen in the spectra of related azabieyelie compounds observed. The most important feature observed in the spectra is the common base peak (m/e 58), which results from the generation of N, N-dimethylformimmonium ion 24. The pathway by which this ion originates is discussed.  相似文献   

6.
Doubly charged ion mass spectra of 23 alkenes have been measured using a double focusing Hitachi RMU-7L mass spectrometer. Ion mass spectra were obtained using 100 eV electron energy and 3.2 kV ion accelerating voltage. Each 2E spectrum was determined using the olefinic compound under investigation as the target gas. In general, spectra are dominated by fragment ions which result from extensive hydrogen loss from the doubly charged molecular ion. Appearnce energies have been measured for intense fragment ions in each spectrum.  相似文献   

7.
The mass spectra of twenty-eight N-substituted 2-aminobenzoxazoles and 2-aminobenzothiazoles have been recorded and the identity of various ions in the mass spectra have been established by high resolution measurement. The molecular compound of series, benzoxazole, undergoes loss of hydrogen cyanide and carbon monoxide from the molecular ion as the most important decomposition pathways. The mass spectra of N-substituted benzothiazoles showed a similar fragmentation as that of N-substituted benzoxazoles.  相似文献   

8.
Summary By high-performance liquid chromatography (HPLC) coupled with UV diode-array detection (DAD) and thermospray mass spectrometry (TSP-MS), four main constituents of a polar, whole plant extract fromDissotis rotundifolia T. were characterized. The fourC-glycosylflavones, isoorientin, orientin, vitexin and isovitexin were detected in the methanolic and hydroalcoholic extract of the plant as well as in the commercial drug preparation ‘Sirop de Dissotis’. Although the UV data and TSP mass spectra allowed rapid characterisation of all fourC-glycosylflavones, exact attribution of the peaks to their structures could not be achieved as neither the UV spectra nor the TSP mass spectra enabled differentiation of one position isomer from the other. Therefore a successful attempt was made to distinguish the 6-C from the 8-C-glycosylflavones by thermospray tandem mass spectrometry (TSP-MS-MS). The collision induced dissociation (CID) spectra of the particular ion [M+H-120]+ gave fragments which permitted differentiation of position isomers. To confirm the accuracy of on-line results, reference compounds were included in the HPLC study.  相似文献   

9.
The H2 and CH4 chemical ionization mass spectra of the olefinic esters methyl acrylate, methyl methacrylate, methyl crotonate, methyl 3-butenoate, methyl 2-methyl-2-butenoate, methyl 3-methyl-2-butenoate and methyl cinnamate have been determined. In addition to the expected loss of CH3OH from [MH]+, in many cases the protonated molecules also show loss of CO or CH2CO with methoxy group migration to the positive ion centre, indicative of protonation at the double bond. These rearrangement reactions, which have analogies in electron impact mass spectra, result in chemical ionization mass spectra of isomeric molecules which show more substantial differences than the electron impact mass spectra. In the case of methyl cinnamate, isotopic labelling experiments show considerable interchange of the added proton with the ortho and meta phenyl hydrogens prior to CH3OH or CH2CO loss, although the extent of interchange is not the same for both cases.  相似文献   

10.
Electrospray ionization (ESI) mass spectra have been measured on a magnetic-sector double-focusing mass spectrometer for a number of proteins and peptides. It is pointed out how in theory raising the mass resolution of a mass spectrometer from 800–1000 to 2400–3000 significantly increases the precision with which the envelope of isotopic peaks of a protein ion (or other organic ion) can be defined, particularly at higher masses. Better definition of the isotopic envelope ought to lead to higher precision in the experimental determination of molecular mass, which has been demonstrated. It is shown how ESI mass spectra of high-mass molecules are significantly less congested at higher m/z values, so that for these molecules (RMM > 40 000) there is an advantage in being able to record peaks at higher m/z values (m/z > 2000) representing ions with fewer charges. Fragmentation of a small peptide in the ESI source has been found to provide sequence information.  相似文献   

11.
De novo sequencing of peptides using tandem MS is difficult due to missing fragment ions in the spectra commonly obtained after CID of peptide precursor ions. Complementing CID spectra with spectra obtained in an ion‐trap mass spectrometer upon electron transfer dissociation (ETD) significantly increases the sequence coverage with diagnostic ions. In the de novo sequencing algorithm CompNovo presented here, a divide‐and‐conquer approach was combined with an efficient mass decomposition algorithm to exploit the complementary information contained in CID and ETD spectra. After optimizing the parameters for the algorithm on a well‐defined training data set obtained for peptides from nine known proteins, the CompNovo algorithm was applied to the de novo sequencing of peptides derived from a whole protein extract of Sorangium cellulosum bacteria. To 2406 pairs of CID and ETD spectra contained in this data set, 675 fully correct sequences were assigned, which represent a success rate of 28.1%. It is shown that the CompNovo algorithm yields significantly improved sequencing accuracy as compared with published approaches using only CID spectra or combined CID and ETD spectra.  相似文献   

12.
The mass spectra of all stereoisomers of decalin-2,3-diol, the corresponding dimethyl ethers and of some deuterated derivatives are discussed. The mass spectra of isomeric decalin-2,3-diols differ only slightly in ion intensities. The mass spectra of the stereoisomeric 2,3-dimethoxy-decalins are nearly identical within the series of transand cisderivatives. A mass spectrometric identification of the stereoisomers of these compounds is therefore diffucult. Stereoselective eliminations from the molecular ion are not observed. The mass spectra -of stereoisomeric decalin-1,4-diols show characteristic differences in the intensities of the[M ? H2O]+˙-ions, which can be related to the geometry of the molecules in a similiar mode as was the case with cyclohexane-1,4-diols, The sterechemical control of the elimination of H2O from the molecular ions has been confirmed by deuterium labelling. The mass spectra of stereoismeric 1,4-dimethoxy-decalins also differ characteristically in the intensities of the [M ? CH3OH]+˙ ions. Furthermore peak due to the [M ? CH2O]+˙ ions are only observed in the mass spectra of those stereoisomers, which have at least one conformation with a short distance between the two methoxy. The stereospecifity of the CH3OH- and CH2O-eliminationjs has also been determined by deuterium labelling.  相似文献   

13.
Glycosides, steviolside, and rubaudioside A, which are extracted from the leaves of Stevia rebaudiana, can be used as sweetener for food additive. Intermediates of steviolbioside, steviol, and isosteviol are very stable compounds obtained from benzotriazol‐1‐yloxtri(pyrrolidinol)phosphonium hexafluorophosphate. They are suitable to be used in amide and amide dimer synthesis. These nature product intermediates possess special characteristics. The spectra data showed two tautomeric groups: an ester form and an amide form. Their nuclear magnetic resonance, mass and chromatographic/mass/mass spectra were examined.  相似文献   

14.
Monensin and nigericin are structurally related compounds belonging to a family of biologically active, polycylic, monocarboxylic acids produced by Streptomyces. Partial interpretation of their mass spectra has been achieved with the aid of high resolution data and by correlation with spectra of derivatives. These results have been applied to structure elucidation of several minor factors produced along with monensin. An interesting aspect of the mass spectrometry of these compounds is that their alkali-metal salts are sufficiently volatile to yield mass spectra. Fragmentation of the salts is markedly different from that of the free acids and their derivatives. A scheme is proposed to account for the formation of a number of fragment ions which contain the metal atom.  相似文献   

15.
The mass spectra of the five stereoisomers of decalin-1,5-diol and its dimethyl ether have been investigated. The differences in the mass spectra of stereoisomers I to III with a trans- decalin ting system are small. The differences are much larger in the mass spectra of the two isomers IV and V of the cis-decalin series and the elimination of CH2O, formed by interaction between the two methoxy groups, from the molecular ion is only observed in the mass spectrum of Vb.  相似文献   

16.
Electron impact mass spectra of 3,5,7-trisubstituted 4H-1,2-diazepines indicate that aryl substituents lead to N2 expulsion while alkyl substitutents do not. A common fragmentation pattern is observed and discussed for all alkyldiazepines, most of which are newly reported compounds. Assignments are based on electron impact mass spectra of deuteriated substrates and high resolution mass spectra. A previous interpretation of N2 expulsion is corrected.  相似文献   

17.
A new scan is described which responds to ions that are intermediates in the dissociation of a mass-selected parent ion (mp) to give a mass-selected daughter ion (md). The scan gives a simple mass v. abundance output for ions which satisfy this condition. It is implemented here on a BEQQ hybrid mass spectrometer using, in sequence, collision-induced dissociation occurring at high energy in the first reaction region, and low-energy collisional activation in the collision quadrupole. The experiment provides information on reaction sequences not available from single scans of other types. In the several cases examined, it is demonstrated that, among many conceivable fragmentation routes connecting a parent ion with a particular fragment ion, only a few are significant. Examination of reaction intermediate spectra also appears to be a fruitful new approach to mechanistic questions, as illustrated by consideration of the behavior of several isomeric octanones. These new spectra also have analytical value: they show good signal-to-noise ratios and allow ready distinction between isobaric and isomeric ions. A comparison of the reaction intermediate spectrum with a daughter spectrum obtained by the B/E linked-scanning technique reveals the contributions of artifact peaks which result from poor parent ion mass resolution in the latter. Reaction intermediate spectra combine information from the daughter spectra of mp and the parent spectra of md and, as a specified portion of this data domain, have unique characteristics.  相似文献   

18.
The mass spectra of several bitter principles isolated from Picrasma ailanthoides Planchon (= P. quassioides Bennett) have been measured and characteristic fragmentation patterns useful for structure elucidation shown. The mass spectra of some related compounds are also described.  相似文献   

19.
Structurally-related alkaloids were analyzed by electrospray ionization/multiple stage mass spectrometry (ESI/MS n ) at varying collision energies to demonstrate a conceptual algorithm, precursor ion fingerprinting (PIF). PIF is a new approach for interpreting and library-searching ESI mass spectra predicated on the precursor ions of structurally-related compounds and their matching product ion spectra. Multiple-stage mass spectra were compiled and constructed into “spectral trees” that illustrated the compounds’ product ion spectra in their respective mass spectral stages. The precursor ions of these alkaloids were characterized and their spectral trees incorporated into an MS n library. These data will be used to construct a universal, searchable, and transferable library of MS n spectra. In addition, PIF will generate a proposed structural arrangement utilizing previously characterized ion structures, which will assist in the identification of unknown compounds.  相似文献   

20.
The characterization of by‐products arising from the UV photodegradation of two insecticide pyrethroids lacking the cyclopropane ring (flucythrinate and fenvalerate) has been investigated by gas chromatography coupled with mass spectrometry (GC/MS). Twenty photoproducts were tentatively identified mainly based on the interpretation of the experimental mass spectra or by using reference mass spectra. Some of these compounds had not previously been detected. Furthermore, the generation of some of the photoproducts might be a matter for concern due to their potential toxicity. The corresponding photodegradation routes, including postulation of the intermediate radicals, have also been proposed. These photodegradation studies were performed by photo‐solid‐phase microextraction (photo‐SPME) in which the SPME fibre was exposed to light after extraction of the target analytes from aqueous solutions. The degradation kinetics of the investigated pyrethroids and the photoformation‐photodegradation curves of the photoproducts generated in situ were also monitored through the ion chromatograms obtained for different irradiation times and the corresponding mass spectra. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

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