Spectrometer operation parameters

A comprehensive discussion and illustrations of the effects of spectrometer operating parameters on ESR spectra are given by the author in Electron spin resonance, in Physical Methods of Chemistry, ed. A. Weissberger and B. W. Rossiter, John Wiley and Sons, Inc., New York, 1972, part IIIA, ch. VI,. 

Table 3 Typical spectrometer operating parameters and detection limits appropriate for the analysis of silicate rocks by WD-XRF spectrometry. Comparison is made with ED-XRF detection... 

Chapter 3 takes up the problem of multi-frequency ENDOR and ESEEM, and illustrates how small stepwise increments of spectrometer operating parameters can enable one to better determine spin-Hamiltonian parameters via a graphical analysis. 

Scanning method. The sequence of control over operating parameters of a mass spectrometer that results in a spectrum of masses, velocities, momenta, or energies. 

All GC-MS analyses were performed on a Hewlett-Packard 5985 quad-rupole mass spectrometer. Pertinent chromatographic and mass spectral operating parameters are described elsewhere (2). Spectra were collected and recorded in the total ion mode. Individual component spectra were manually compared with U.S. Environmental Protection Agency-National Institutes of Health (USEPA-NIH) library spectra to provide component identifications. All quantitative data were provided as referenced to the dio-anthracene internal standard. 

While our research was concerned with developing wet chemical methods, we confirmed our data with analyses from an available spark source mass spectrometer (SSMS). The SSMS operating parameters are given in Table I. The instrument used was an AEI MS-7 (I, 2) equipped with electrical detection. It was used in the peak switching mode only to provide more precise analyses. 

A critical review of the inherent limitations of modern PFA analytical methods is available in Martin et al. [18], but some examples are discussed here. For quantitative determination, the HPLC system is often interfaced to a Micromass or Sciex tandem mass spectrometer operated in the negative ion electrospray mode. Instrumental parameters are optimized to transmit the [M - H] ion for all analytes (Table 5). When possible, multiple daughter ions are monitored, but quantitation is generally based on a single product ion (Table 5, Fig. 4). In the electrospray tandem mass spectrometry (ES MS/MS) system, the 499 Da -> 80 Da transition can provide a stronger signal than... 

With regard to analysis, there could be a different set of operating parameters for the analyzer instrument that would result in improved calibration data. For example, for an FTIR spectrometer, one could decrease the spectral resolution to obtain a better spectral S/N for the same total scan time. Such a strategy could be advantageous if the spectral features being used for calibration have relatively low resolution. There could also be specific sets of instrument-operating parameters where the instrument response is noisy or unstable over time, in which case they can be changed to improve precision and stability of the analyzer data. 

Natural abundance 13c spectra were obtained using quadrature detection modified Bruker HX-270 and HFX-90 spectrometers operating at 67.9 and 22.6 MHz, respectively. Free induction decays were accumulated using 4K/4K data points and a 3kHz spectral window. A fast inversion recovery (FIRFT) pulse sequence (21) was employed to measure T] s T] s were calculated using a nonlinear three parameter fitting procedure(22). 

After the optimum GC conditions and MS mode have been selected, the operating parameters of the GC-MS spectrometer are set accordingly. When the initial oven temperature attains an equilibrium state, a sample solution in the range of 2-5 p is injected into the gas chromatograph. The amount of sample injected depends on the number and the concentration of the constituents in the sample solution. The constituents are separated in the capillary column and continuously introduced into the ion source of the MS system at a pressure in the order of 10-6 to 10-7 Torr, whereupon the mass spectra corresponding to the individual components in the sample are generated. Irrespective of the MS operational mode used, the mass spectra thus produced are scanned... 

The main components of an LC-MS are the HPLC apparatus, an optional UV or photodiode array detector, the interface, the mass spectrometer and a computer system for data management and evaluation. The interface is the key component of the LC-MS system. All other components must be adapted to the particular interface that is used. Most commercially available systems work with thermospray, electrospray, or particle beam interfaces. Each interface has a distinct mode of action and its own operational parameters. 

The mass spectrometer may be divided into a number of discrete components a sample inlet, an ion source, one or more analyzers, a detector, and finally, a computer to both collect data and control the operational parameters of the instrument (Figure 1). In principle, gas-phase neutral molecules are ionized so that they may be separated by the electric and / or magnetic fields of the analyzer according to their mass (m) to charge (z) ratios (m/z). The ions are then detected and recorded as a mass spectrum, graphing the ion abundance against the m/z ratio of the individual ions (Figure 2). 

Other instrumental considerations are computer related and include factors such as memory size, word length and ADC resolution (9). Most modern FT nmr spectrometer systems are designed to satisfy the above requirements, but one must always verify proper operating parameters for the analysis being run. 

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