High-resolution double focusing mass spectrometer

An interface has been connected to a high-resolution double-focusing mass spectrometer applied to the analysis of mixtures of both chemically synthesized peptides and peptides obtained from proteolytic digests of proteins. Detection limits of about 35 fmol were reported. Reinhold et al.73 described the on-line coupling of CE and MS using a CF-FAB system in... 

The molecular ion overlaps due to plasma and solvent species are most severe below mass/charge 82. A high-resolution, double-focusing mass spectrometer was used to identify molecular ions observed in ICP-MS (Table 3.3) [3]. Common molecular ions that produce intense signals from plasma and solvent species include ArO+, ArOH+, ArH+, ArN+, Ar+, Ar2H+, 0+, N2+, NO+, and 0+. Other molecular ions become a problem at lower analyte concentrations. These include CO, CO H+, NOt, ArO+ ions with minor isotopes of Ar or O, ArC+, ArN+, and minor isotopes of Ar as ArJ. 

C. The High-Resolution Double-Focusing Mass Spectrometer. 153... 

This article describes recent advances in the experimental determination of electron impact ionization cross sections for silane (SiH4) its radicals, SiH. (x = 1 to 3) and the Si-organic molecules tetramethylsilane (TMS), Si(CH3)4 tetraethoxysilane (TEOS), Si(0-CH2-CH3)4 and hexamethyldisiloxane (HMDSO), (CH3)3-Si-0-Si-(CH3)3, which is one of the simplest siloxane compounds. These are model substances, and the results obtained for these species may be used in efforts to predict the ionization properties of other, more complex Si-organic molecules. The ionization cross sections of the stable compounds were measured using a high-resolution double-focusing mass spectrometer. The cross-section data for the radicals were obtained in a fast-neutral-beam apparatus. 

In the following sections of this article, we describe the principles of ionization cross-section measurements, including a brief description of the fast-beam apparatus and the high-resolution double-focusing mass spectrometer employed in the present studies. A comprehensive review of semiempirical calculations of total ionization cross sections is given. Comparisons between these calculated cross sections and the experimental results are presented. The decomposition of the various molecules in a low-temperature plasma is discussed on the basis of the measured ionization-cross-section data, and comparisons are made with the results of in situ plasma diagnostics studies using mass spectrometric techniques. 

Fig. 2. Schematic diagram of the high-resolution double-focusing mass spectrometer. The insert shows an enlarged view of the ion extraction optics for the high-extraction-efficiency mode. P, pusher electrode C, collision chamber B, electron beam (z direction) S, collision chamber exit slit S2, penetrating field extraction slit S3, grounded slit S4 and Ss, deflector electrodes.

High-resolution double-focusing mass spectrometers... 

Double-focusing mass spectrometer A mass spectrometer consisting of electrostatic and magnetic sector analysers capable of achieving high-mass spectral resolution. 

Exact mass measurement at high resolution is an important tool along with other spectroscopic methods to help confirm the structure of novel flavonoids. It is used as structural proof when elemental analysis is not possible, e.g., when studying minor components. When EI-MS can be used, 1 to 10 pmol samples are required for one measurement however, when FAB-MS is used, 0.1 to 1 nmol is normally required. The use of ESI on a double focusing mass spectrometers and MALDI-TOF-MS requires smaller amounts of sample, and subpi-comole amounts of flavonoids may be adequate. 

Double-focusing mass spectrometers with high mass resolution are rather bulky and expensive instruments so that the development of single magnetic sector field mass spectrometers was of significance in the following years. 

Double-focusing mass spectrometers with Mattauch-Herzog geometry and high mass resolution have been used for a long time, especially in nuclear physics, for the precise determination of exact... 

Explain how a double-focusing mass spectrometer achieves high resolution. 

Low Voltage Mass Spectrometry of Macrocyclic Extractables. Nominal parent mass analyses of the macrocyclic extractables, obtained from typical polymerization products of cyclooctene and 1,5-cyclooctadiene, were performed on a Model MS-9 double focusing mass spectrometer (Associated Electrical Industries, England) at a resolution of 1/1000 and an emission of 7.0 e.v. Samples were introduced directly into the source chamber by the direct-probe technique. The temperature range during the experiment was 125°-200°C., and the source pressure was maintained in the 0.1-3 X 10-6 torr range. In addition, a high resolution measurement was carried out on the mass number 220 to identify the two components present at that mass number. 

There are many types of mass spectrometer, from high-resolution double-focusing instruments, which can distinguish molecular and fragment masses to six decimal places, to bench-top machines with a quadrupole mass detector which can resolve masses up to about m/z = 500, but only in whole-number differences. Routinely you are most likely to encounter data from bench-top instruments and therefore only this typie of spectrum will be considered. 

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