摘要:

AbstractThe noise in a sector or quadrupele mass spectrometer is determined by the source, i.e. the number of ions present in the signal, whereas in Fourier‐transform ion cyclotron resonance it is detector limited. In addition, the Fourier transform spreads white noise equally over the whole spectrum. Thus the accuracy for broad‐band spectra is generally rather low. However, the precision, i.e. the reproducibility of successive spectra, is astonishingly high. This fact has been used with much success, for example in collisionally activated dissociation in Hadamard spectra. It is shown that photofragmentation spectra are also very reproducible and thus allow—at least in principle—a ‘kinetic deconvolution’ of a series of such spectra. In such a case, nonlinear regression has to be applied to the data. Since in most kinetics problems several exponential functions are involved, and since it is well known that these exponential functions are notoriously difficult to approximate with a Marquardt‐Levenberg algorithm, the validity of the results may be questionable. Three examples (protonated benzene, cycloheptatriene, deuterated toluene) are chosen to demonstrate some of the difficulties and pitfalls of

ISSN:0951-4198    

DOI:10.1002/rcm.1290080102

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractA short overview of current excitation and detection techniques for Fourier‐transform mass spectrometry and related ion cyclotron resonance experiments is given, and some ideas are discussed which may lead to new development

ISSN:0951-4198    

DOI:10.1002/rcm.1290080103

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractA general scheme for ionization and fragmentation of ions in Fourier‐transform ion cyclotron resonance mass spectrometry (FT‐ICRMS) is introduced. The technique is based upon excitation of high‐frequency (i.e. lowmass) primary ions (e.g. N +·2, Al+, H2O+·) which may be generated by standard ionization methods (e.g. electron ionization or laser desorption) inside the trap. Generation of the primary ions is followed by excitation of their cyclotron motion to high translational energy to serve as projectile ions. The projectiles serve two functions: to ionize neutral gas atoms and/or molecules (secondary ions) within the trap internal ion impact ionization (IIII), and to collisionally activate the secondary ions to induce fragmentation. Ionization by IIII is analogous to charge‐exchange ionization, in which a primary ion reacts with neutral analyte to produce ionization. When the projectile ions' cyclotron orbits are not excited (even for very long delay periods between ionization and detection), lower ion abundances are observed for the secondary ions derived from the neutral analyte(s), verifying that high energy ion impact must be responsible for the relatively high ion abundances observed when projectile cyclotron motion is excited: i.e., the mechanism of IIII is likely to be high‐energy charge exchange. Several advantages of the new technique include: accessibility of very high impact energy (keV) in FT‐ICRMS in both the laboratory and the center‐of‐mass frames of reference; ease in controlling the average energy transferred from projectiles to sample neutrals by moderation of the projectile ion's cyclotron radius; and the high ion‐molecule reaction rates attainable in FT‐ICR due to the long path length for trapped primary projectile ions at low pressure. Theory of ion formation and the problems associated with this technique (e.g. formation of secondary ions at different pre‐excitation

ISSN:0951-4198    

DOI:10.1002/rcm.1290080104

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractUntil the present, analysis of aqueous solutions of atrazine has been conducted using a combination of liquid chromatography or gas chromatography with mass spectrometry, after a preconcentration step. We explore herein a new approach for studying support‐phase‐extracted atrazine and hydroxyatrazine samples. Solid‐phase extraction membranes are inserted directly into the cell of a Fourier‐transform mass spectrometer for analysis after laser ionization. It appears that atrazine and its metabolite have very different ionization processes. In the case of hydroxyatrazine, the [M + H]+ion signal can be correlated to the concentration of the extracted solution. These encouraging results might open the route to a quantification

ISSN:0951-4198    

DOI:10.1002/rcm.1290080105

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractThe use of binary matrices and internal calibrants to improve the mass measurement accuracy in matrix‐assisted laser desorption ionization (MALDI) with Fourier‐transform ion cyclotron resonance (FTICR) mass spectro‐metry is described. Binary matrices enhance the analyte ion yield and enable a complete MALDI‐FTICR mass spectrum to be obtained from a single laser shot. The advantage of single‐laser‐shot data acquisition is that it eliminates line‐broadening due to shot‐to‐shot frequency variations. It is shown that unresolved product ions, mainly due to loss of H2O and/or NH3, shift the centroid of an unresolved multi‐component peak. A mass measurement accuracy of 12 ppm was obtained for the bovine insulin [M+H]+ion using melittin as an

ISSN:0951-4198    

DOI:10.1002/rcm.1290080106

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractFocused‐laser ionization of solids and subsequent analysis of the generated ions by Fourier‐transform mass spectrometry is suitable for the characterization of inorganic and organic constituents. This paper describes selected examples to illustrate the capability of structural characterization of inorganic substances and the problems associated with the critical nature of the energy deposition phenomena which can complicate the use of the method. Selected examples from practical problem solving in material applications are presented to evidence the feasibility of local analysis by Fourier‐transform laser microprobe mass spectro

ISSN:0951-4198    

DOI:10.1002/rcm.1290080107

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractThe recently developed FT LMMS with an external ion source has been applied to selected organic molecules. Some aspects of the ion formation processes from solids under focused laser irradiation at 266 nm were investigated. Specifically, the effect of laser energy and the time profile of ion production were studied. First, the generation of intact cations, fragments and thermal decomposition products from a quaternary ammonium salt were evaluated at distinct times after the laser pulse. The mass spectra of phenol red in its neutral and salt form were recorded under different conditions with respect to laser irradiation power density conditions and ion formation after the laser pulse. The results allow the refinement of previous concepts about ionization in LMMS.

ISSN:0951-4198    

DOI:10.1002/rcm.1290080108

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractThe application of Fourier‐transform laser microprobe mass spectrometry to lichens is described. Thein situdetection of a new perylene quinone in samples of the tropical speciesLaurera sanguinariaMalme andGraphis haematitesFée was achieved with minimal specimen preparation. The high mass resolution and mass accuracy of the instrument eliminates the need for additional characterization of the isolated substances by high resolution electron impact mass spectrometry and direct introduction pro

ISSN:0951-4198    

DOI:10.1002/rcm.1290080109

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractFour dominant reactions can be observed when the β‐distonic ion·CH2CH2OH +2reacts in the cell of a Fourier‐transform ion cyclotron resonance spectrometer with a number of neutral molecules: protonation of the neutral molecule, ethylene radical‐cation transfer, hydride abstraction from the neutral molecule, and charge exchange. Among the ethylene transfer reactions, which can lead to a variety of other distonic ions, we have throroughly studied the reaction with formaldehyde. The reaction of a first molecule of CH2O yields·CH2CH2OCH +2. The addition of a second one leads to 1,3‐dioxane which stabilizes by H·loss. This latter reaction i

ISSN:0951-4198    

DOI:10.1002/rcm.1290080110

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractThe gas phase of hexanuclear Ta clusters of type [Ta6X12]X2·8H2O, X=Cl, Br was investigated using laser‐desorption Fourier‐transform mass spectrometry. The [Ta6X12]X 2−ions (m/z=1581 for X=Cl,m/z=2205 for X=Br) are the most characteristic peaks in their negative‐ion laser‐desorption mass spectra. Additional fragmentations observed are the result of loss of halogen and metal from [Ta6X12]X 2−. Positive ions are observed only in the laser‐desorption mass spectra o

ISSN:0951-4198    

DOI:10.1002/rcm.1290080111

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY