Spectrometer comparisons

Figure 9 The effect of the presence of water vapour on Fourier selfdeconvolution. The solid trace is the spectrum of the same sample as in Figure 8A recorded without adequate purging of the spectrometer. Comparison of the spectrum obtained after Fourier selfdeconvolution (dashed line) with that in Figure 8C reveals the appearance of additional bands due to water vapour.

Wada, Y. Tamura, J. Musselman, B. D. Kassel, D. B. Sakurai, T Matsuo, T. Electrospray ionization mass-spectra of hemoglobin and transferrin by a magnetic-sector mass-spectrometer—Comparison with theoretical isotopic distributions. Rapid Commun. Mass Spectrom. 1992, 6, 9 13. 

Schumann and Lomheim (2002) Infrared Hyperspectral Imaging Fourier Transform and Dispersive Spectrometers Comparison of Signal-to-Noise-Based Performance by L. W. Schumann and T. S. Lomheim, Proc SPEI 4480,... 

Assuming that the mass spectrometer has sufficient mass resolution, the computer can prepare accurate ma.ss data on the m/z values from an unknown substance. To prepare that data, the system must acquire the mass spectrum of a known reference substance for which accurate masses for its ions are already known, and the computer must have a stored table of these reference masses. The computer is programmed first to inspect the newly acquired data from the reference compound in comparison with its stored reference spectrum if all is well, the system then acquires data from the unknown substance. By comparison and interpolation techniques using the known reference... 

Nonfractionating continuous inlet. An inlet in which gas flows from a gas stream being analyzed to the mass spectrometer ion source without any change in the conditions of flow through the inlet or by the conditions of flow through the ion source. This flow is usually viscous flow, such that the mean free path is very small in comparison with the smallest dimension of a traverse section of the channel. The flow characteristics are determined mainly by collisions between gas molecules, i.e., the viscosity of the gas. The flow can be laminar or turbulent. 

As in all Fourier transform methods in spectroscopy, the FTIR spectrometer benefits greatly from the multiplex, or Fellgett, advantage of detecting a broad band of radiation (a wide wavenumber range) all the time. By comparison, a spectrometer that disperses the radiation with a prism or diffraction grating detects, at any instant, only that narrow band of radiation that the orientation of the prism or grating allows to fall on the detector, as in the type of infrared spectrometer described in Section 3.6. 

Figure 10 shows a comparison of Scofield s calculated values with experimentally measured values (24) which, in addition to (, are dependent on spectrometer transmission function. The overall agreement between the calculated and experimental values is quite good. The far rightjy-axis in Figure 10 indicates the experimentally accessible surface sensitivities in monolayers (ML) as a function of atomic number. For most elements, sensitivities on the order of 1% of a ML are achievable. 

In Secondary Ion Mass Spectrometry (SIMS), a solid specimen, placed in a vacuum, is bombarded with a narrow beam of ions, called primary ions, that are suffi-ciendy energedc to cause ejection (sputtering) of atoms and small clusters of atoms from the bombarded region. Some of the atoms and atomic clusters are ejected as ions, called secondary ions. The secondary ions are subsequently accelerated into a mass spectrometer, where they are separated according to their mass-to-charge ratio and counted. The relative quantities of the measured secondary ions are converted to concentrations, by comparison with standards, to reveal the composition and trace impurity content of the specimen as a function of sputtering dme (depth). 

Isotope shifts for most elements are small in comparison with the bandwidth of the pulsed lasers used in resonance ionization experiments, and thus all the isotopes of the analyte will be essentially resonant with the laser. In this case, isotopic analysis is achieved with a mass spectrometer. Time-of flight mass spectrometers are especially well-suited for isotopic analysis of ions produced by pulsed resonance ionization lasers, because all the ions are detected on each pulse. 

In the infrared spectral range in general Fourier transform (FT) interferometers are used. In comparison with dispersive spectrometers FTIR enables higher optical throughput and the multiplex advantage at equivalent high spectral resolution. In... 

Figure 10. Comparison of the velocity dependence of the disappearance cross-section of CHa+, formation cross-section of CH0 +, and Langevin orbiting collision cross-section, all as a function of reciprocal average kinetic energy of ions in the mass spectrometer source...

A number of different types of HPLC detector have been discussed in the previous chapter. In comparison to these, a mass spectrometer is a relatively expensive detector and there need to be considerable advantages associated with its use to make the significant financial investment worthwhile. What are these advantages In order to answer this question, we must first consider what it is we are trying to achieve when using chromatography ... 

Table 5.21 Intra-assay precision and accuracy of theLC-MS-MS determination of Idoxifene using a triple-quadrupole mass spectrometer. Reprinted from J. Chromatogr., B, 757, Comparison between liquid chromatography-time-of-flight mass spectrometry and selected-reaction monitoring liquid chromatography-mass spectrometry for quantitative determination of Idoxifene in human plasma , Zhang, H. and Henion, J., 151-159, Copyright (2001), with permission from Elsevier Science...

For a comparison of experimental Mossbauer isomer shifts, the values have to be referenced to a common standard. According to (4.23), the results of a measurement depend on the type of source material, for example, Co diffused into rhodium, palladium, platinum, or other metals. For Fe Mossbauer spectroscopy, the spectrometer is usually calibrated by using the known absorption spectrum of metallic iron (a-phase). Therefore, Fe isomer shifts are commonly reported relative to the centroid of the magnetically split spectrum of a-iron (Sect. 3.1.3). Conversion factors for sodium nitroprusside dihydrate, Na2[Fe(CN)5N0]-2H20, or sodium ferrocyanide, Na4[Fe(CN)]6, which have also been used as reference materials, are found in Table 3.1. Reference materials for other isotopes are given in Table 1.3 of [18] in Chap. 1. 

Fig. 4.7.7 A portable NMR system for measuring freeze damage in Navel oranges. The Halbach magnet is shown above the completed system with two Navel oranges for comparison. The complete system has the battery powered spectrometer electronics housed in a metal box and the system is run by a portable computer.

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