Mass spectrometry complex spectra

Laali and Lattimer (1989 see also Laali, 1990) observed arenediazonium ion/crown ether complexes in the gas phase by field desorption (FD) and by fast atom bombardment (FAB) mass spectrometry. The FAB-MS spectrum of benzenediazonium ion/18-crown-6 shows a 1 1 complex. In the FD spectrum, apart from the 1 1 complex, a one-cation/two-crown complex is also detected. Dicyclo-hexano-24-crown-6 appears to complex readily in the gas phase, whereas in solution this crown ether is rather poor for complexation (see earlier in this section) the presence of one or three methyl groups in the 2- or 2,4,6-positions respectively has little effect on the gas-phase complexation. With 4-nitrobenzenediazonium ion, 18-crown-6 even forms a 1 3 complex. The authors assume charge-transfer complexes such as 11.13 for all these species. There is also evidence for hydride ion transfer from the crown host within the 1 1 complex, and for either the arenediazonium ion or the aryl cation formed from it under the reaction conditions in the gas phase in tandem mass spectrometry (Laali, 1990). 

GC-IMS-MS instruments are ideally suited for laboratory studies, as a complex mixture can be separated ionisation in relatively clean systems can take place and the identity of the ions can be studied and verified by mass spectrometry [315]. However, the cost of such systems is quite prohibitive, and their complexity confines their utilisation to the laboratory. In GC-IMS-MS, the gas chromatograph is used to preseparate the components of the sample, with the IMS used as its detector. The ions that constitute the mobility spectrum are then further characterised by MS. 

Detailed examination of another madder preparation proved that the sample can be premordanted with alum. [ 19] After hydrolysis performed with hydrochloric acid and extraction with M-amyl alcohol, only four colourants are found alizarin, purpurin, and probably lucidin and ruberythric acid. Additionally, signals at m/z 525 and 539 are observed in the mass spectrum. Analysis of the preparation by inductively coupled plasma mass spectrometry (ICP MS) shows that aluminium and calcium are the main inorganic components of the sample. This is why it was suggested that the signal at m/z 539 can be attributed to the complex of aluminium with alizarin, and the second one, observed at m/z 525, to an aluminium-calcium cluster. 

Smith [83] classified large sets of hydrocarbon oil infrared spectral data by computer into correlation sets for individual classes of compounds. The correlation sets were then used to determine the class to which an unknown compound belongs from its mass spectral parameters. A correlation set is constructed by use of an ion-source summation, in which a low resolution mass spectrum is expressed as a set of numbers representing the contribution to the total ionisation of each of 14 ion series. The technique is particularly valuable in the examination of results from coupled gas chromatography-mass spectrometry of complex organic mixtures. 

Attempts to crystallize a phosphonato complex invariably led to the formation of glassy materials. For example, a solid compound was obtained that analyzed as K2Be(H2mdp)2 2H20. Electrospray mass spectrometry spectra of this product confirm the stoichiometry the most abundant peaks corresponded to the formulas [Be(H2mdp)2]2 in the negative ion ESMS spectrum and K8[Be(H2mdp)] + in the positive ion ESMS spectrum (260). 

Rarely will it be possible to draw conclusions directly from the raw data of analytical measurements and it is usual for some refinement of the data to be carried out. In its simplest form this could merely comprise background corrections, but it is often much more complex, requiring corrections for a number of factors as in mass spectrometry, X-ray fluorescence and electron probe microanalysis. More complex routines made available by computers include spectrum smoothing, stripping one component from a spectrum or making peak area measurements from chromatograms. 

To record a mass spectrum it is necessary to introduce a sample into the ion source of a mass spectrometer, to ionize sample molecules (to obtain positive or negative ions), to separate these ions according to their mass-to-charge ratio (m/z) and to record the quantity of ions of each m/z. A computer controls all the operations and helps to process the data. It makes it possible to get any format of a spectrum, to achieve subtraction or averaging of spectra, and to carry out a library search using spectral libraries. A principal scheme of a mass spectrometer is represented in Fig. 5.2. To resolve more complex tasks (e.g., direct analysis of a mixture) tandem mass spectrometry (see below and Chapter 3) may be applied. 

There are at least three possibile ways in which the inhibitor can bind to the active site (1) formation of a sulfide bond to a cysteine residue, with elimination of hydrogen bromide [Eq. (10)], (2) formation of a thiol ester bond with a cysteine residue at the active site [Eq. (11)], and (3) formation of a salt between the carboxyl group of the inhibitor and some basic side chain of the enzyme [Eq. (12)]. To distinguish between these three possibilities, the mass numbers of the enzyme and enzyme-inhibitor complex were measured with matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI). The mass number of the native AMDase was observed as 24766, which is in good agreement with the calculated value, 24734. An aqueous solution of a-bromo-phenylacetic acid was added to the enzyme solution, and the mass spectrum of the complex was measured after 10 minutes. The peak is observed at mass number 24967. If the inhibitor and the enzyme bind to form a sulfide with elimination of HBr, the mass number should be 24868, which is smaller by about one... 

Two isomeric complexes, 60 and 61, have been analyzed by Cl MS (reagent gas CH4), producing [M -b I] and [M -b 29]+ ions. Electron ionization mass spectrometry was applied in the analysis of the product of the reaction between Zn(CF3)Br-2CH3CN (62) and 4-(Af,Af-dimethylamino)pyridine (DMAP). The El (20 eV) mass spectrum of the product, Zn(CF3)Br DMAP (63), was recorded at 280 °C and consisted mainly of [C6H3BrF2NZn]+, [ZnBr2]+ and [ZnBr]+ ions. At lower temperatures, this compound did not yield any Zn-containing ions, and the spectra were dominated by the peaks of the [DMAPJ+ and [C2HgN]+ ions . 

Secondary-ion mass spectrometry (SIMS) has been applied to the study of some silver complexes.511 For [Ag(py)4]S208 however, although the spectrum obtained was rich in fragment ions, no AgL spedes could be detected. Doubly charged spedes are not commonly observed in SIMS analyses and the reduced form of the intact cation, i.e. [Ag(py)4]+, was apparently not sufficiently stable in the gas phase. 

Secondary-ion mass spectrometry (SIMS) of [Ag(bipy)2]2+ yields a spectrum identical to that of the silver(I) complex, showing peaks attributable to (L + H)+, Ag+ and AgL+. This suggested facile reduction occurred to the unipositive cation. 30... 

Other aspects of the report (42) on [Fe3S2(NO)5] are surprising. Elemental analysis of the ammonium salt was reported to distinguish between iron(II) and iron(III) in [Fe3S2(NO)5] , but to find these two types of iron present in equal numbers is most unusual for a triiron complex. Second, the molecular weight of the potassium salt was measured as 420 by mass spectrometry. This value is close to the M/Z of 421 calculated for the most abundant isotopic form of the ion-pair cation [KFe3S2(NO)5] +. Finally, the ESR spectrum reported is that of a dini-trosyliron species, which bears a remarkable resemblance to that reported (22) for a complex formed from Fe(II) and nitric oxide in aqueous alkaline solution. 

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