MS data

In contrast to IR and NMR spectroscopy, the principle of mass spectrometry (MS) is based on decomposition and reactions of organic molecules on theii way from the ion source to the detector. Consequently, structure-MS correlation is basically a matter of relating reactions to the signals in a mass spectrum. The chemical structure information contained in mass spectra is difficult to extract because of the complicated relationships between MS data and chemical structures. The aim of spectra evaluation can be either the identification of a compound or the interpretation of spectral data in order to elucidate the chemical structure [78-80],... 

This hybrid is used in one form to measure highly accurate m/z values to obtain excellent elemental compositions of ions and therefore molecular formulae from molecular ions in the other form, it is used to obtain MS/MS data at high resolution. 

Miscellaneous. NIST has a reference database of criticaUy evaluated x-ray photoelectron and Auger spectral data, which is designed to mn on PCs. It is searchable by spectral lines as weU as by element, line energy, and chemical data (82). The Nuclear Quadrapole Resonance Spectra Database at Osaka University of over 10,000 records is avaUable in an MS-DOS version (83). The NCLl system, SDBS, has esr and Raman spectra, along with nmr, ir, and ms data, as described. 

Applications. The capabiHties of a gc/k/ms in separating and identifying components in complex mixtures is very high for a broad spectmm of analytical problems. One area where k information particularly complements ms data is in the differentiation of isomeric compounds. An example is in the analysis of tricresyl phosphates (TCPs) used as additives in a variety of products because of thek lubricating and antiwear characteristics (see Lubrication and lubricants). One important use of TCPs is in hydrauHc fluid where they tenaciously coat metal surfaces thereby reducing friction and wear. Tricresyl phosphate [1330-78-5] (7.2 21 exists in a variety of isomeric forms and the commercial product is a complex mixture of these isomers. 

An investigation of acylaziridines was carried out by comparison of IR, NMR and MS data and included some 1,2-dibenzoylaziridines as well as 2-p-nitrobenzoyl-3-phenyl-oxaziridine (68IZV1530). Amide conjugation in acylated nitrogen-containing three-membered rings is weaker than in open chain acid amides. 

Integration of the H-NMR spectrum shows 55% of tetramer proportions of individual isomers were estimated from GC/MS data. Tetramer mixtures show an asymmetrical, vinyl resonance centered at S 5.40, and asymmetrical, methyl resonances centered at 8 1.70 ( vs. Me4Si in CS2 solution). Integration of the H-NMR spectrum. 

Azides 2a-g were characterized by their elemental analysis, IR, IR and 13c NMR spectra (including INAPT measurements to support the assignations of 13c NMR spectra) and MS data. 

Confirmation of Amino Acid Sequence Using the Analysis of LC-MS Data from an Enzyme Digest of a Protein 152... 

I have tried to make it clear that the LC-MS combination is usually more powerful that either of the individual techniques in isolation and that a holistic approach must be taken to the development of methodologies to provide data from which the required analytical information may be obtained. Data analysis is of crucial importance in this respect and for this reason the computer processing of LC-MS data is considered in some detail in both Chapters 3 and 5. 

It should not be concluded that the above examples of the evaluation of qualitative and quantitative data comprise an exhaustive analysis of this particular set of LC-MS data. They have been included primarily for those not used to the analysis of mass spectral data, to show the principles involved, and to demonstrate how powerful the mass speedometer can be as a chromatographic detector. 

The presence of three polypeptides in Table 5.8 tliat were not predicted from the relationship between the amino acid sequence and the enzyme used for digestion is worthy of note when interpretation of data of this sort is undertaken. The MALDI data showed six further unexpected polypeptides, none of which were detected in the LC-MS data ... 

While there is a vast range of different drug structures, there are only a relatively small number of chemical reactions, some of which are shown below in Table 5.13 (p. 199), involved in the production of metabolites. Based on the structure of the drug, it is therefore possible to predict the most likely metabolites. Use may then be made of reconstructed ion chromatograms (RlCs) of mlz values corresponding to the predicted molecular weights of these metabolites to locate them within the LC-MS data obtained. 

The MS-MS data from metabolite 4 shows a series of ions, i.e. m/z 481, 437 and 380, at m/z values which are 16 greater than those in the MS-MS spectrum... 

The MS-MS data from metabolite 5 shows a base peak at m/z 437, at an increase of 16 Da over the parent drug, but, in common with Indinavir, ions at m/z 364 and 465. Of most significance is the ion at m/z 465 which indicates that the extra oxygen atom is associated with the indan ring structure. 

One of the features of an ion-trap is that ion selection is carried out in time rather than space. In this type of instrument, MS-MS data are generated by ionizing the analyte of interest in the normal way but then, instead of causing ions of all m/z values to become unstable and reach the detector, ions other than those being studied by MS-MS are ejected from the trap. The selected ion is then caused to fragment, in the trap, and the ions so generated are made unstable in order to generate the MS-MS spectrum. The procedure may then be... 

The general procednre is to nse reconstrncted ion chromatograms at appropriate m/z values in an attempt to locate componnds of interest and then look at the mass spectrum of the unknown to determine its molecnlar weight. MS-MS can then be employed to obtain spectra from this and related compounds to find ions that are common to both and which may therefore contain common stmctmal features. Having the same m/z value does not necessarily mean the ions are identical and further MS-MS data or the elemental composition may be required. If these data do not allow unequivocal structure identification, then further MS" information may be required. 

Ciguatoxin. The toxin was isolated from moray eels and purified to crystals by Scheuer s group (1). Structural determination of the toxin by x-ray or NMR analyses was unsuccessful due to the unsuitability of the crystals and due to the extremely small amount of the sample. The toxin was presumed to have a molecular formula of C Hg NO from HRFAB-MS data (MH+, 1111.5570) and to have six hydroxyls, five methyls, and five double bonds in the molecule (2). The number of unsaturations (18 including the five double bonds) and the abundance of oxygen atoms in the molecule point to a polyether nature of the toxin. The toxin, or a closely related toxin if not identical, is believed to be the principal toxin in ciguatera. Ciguatoxin was separable on an alumina column into two interconvertible entities presumably differing only in polarity (J). 

APCl in positive mode ionization and triple quadrupole detection was used for determination of free and bound carotenoids in paprika, obtaining the [M + H]+ and losses of fatty acids as neutral molecules from the [M + H]+ with MeOH, MTBE, and H2O as eluent from the C30 column. The positions of the fatty acids on unsymmetrical xanthophylls could not be established by the MS data. 

This work has been supported by the Norwegian Research Council, project no 100594/410. The authors are indebted to Finn Tpnnesen for recording the GC-MS data. 

The GC-MS data of fraction 1 revealed a strong peak of verticilla-4(20),7,ll-triene (compound 1) accompanied by small amounts of cembrane A and cembrane C. To purify the violet spot and isolate compound 1, it was necessary to reduce the solvent strength. In the mobile phase dichloromethane-hexane (9 + 1 v/v), the development time decreases, which leads to minor diffusion of the zone. The zone of (compound 1) was marked by X = 254 nm UV light. To exclude the impurities, the separation process had to be repeated several times. The zone was removed from the glass plate and eluted from die adsorbent with dichloromethane. The concentrated solution achieved was applied onto a TLC plate as well as injected onto a GC column the... 

The GC-MS data (Figure 16.11) of the violet zone of B. carterii revealed that the unchanged diterpenes (verticillatriene, cembrene A, and cembrene C) and the nortriterpenes with carbohydrate structure originated from the pyrolyzed triterpenes (Figure 16.12) of the a- and (3-boswellic acids, named 24-norursa-3,12-diene (compound 7), 24-norursa-3,9(ll),12-triene (compound 8), 24-noroleana-3,12-diene (compound 9), and 24-noroleana-3,9(ll),12-triene (compound 10). 

The full-scan mode is needed to achieve completely the full potential of fast GC/MS. Software programs, such as the automated mass deconvolution and identification system (AMDIS), have been developed to utilize the orthogonal nature of GC and MS separations to provide automatically chromatographic peaks with background-subtracted mass spectra despite an incomplete separation of a complex mixture. Such programs in combination with fast MS data acquisition rates have led to very fast GC/MS analyses. 

Instrumentation. H and NMR spectra were recorded on a Bruker AV 400 spectrometer (400.2 MHz for proton and 100.6 MHz for carbon) at 310 K. Chemical shifts (< are expressed in ppm coupling constants (J) in Hz. Deuterated DMSO and/or water were used as solvent chemical shift values are reported relative to residual signals (DMSO 5 = 2.50 for H and 5 = 39.5 for C). ESl-MS data were obtained on a VG Trio-2000 Fisons Instruments Mass Spectrometer with VG MassLynx software. Vers. 2.00 in CH3CN/H2O at 60°C. Isothermal titration calorimetry (ITC) experiments were conducted on a VP isothermal titration calorimeter from Microcal at 30°C. 

All MS/MS data was obtained on a Finnigan 3200 spectrometer modified for triple quadrapole work. 

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