Spectrometer settings

Figure 8.5 Mass chromatogram for m/z = 71. This is obtained by running the GC-MS with the mass spectrometer set to register only ions with m/z = 71. It shows a homologous series of -alkanes.

In the first part of this contribution the general principle of multiple frequency selective excitation is explained, followed by a short presentation of correspondingly updated selective ID and 2D pulse sequences and by a few applications and results for demonstration. The contribution concludes with a critical discussion of advantages and limitations for this kind of experiments and the perspectives for further developments. Readers interested in a more detailed description and in experimental details such as spectrometer settings are referred to the corresponding publications [2-6]. 

The low-resolution mass spectrum of Indinavir sulfate was measured using fast atom bombardment mass spectrometry on a JEOL HXl lOA mass spectrometer set at a resolution of 5000. The sample was ionized from a 5 1 dithiothreitol dithioerythritol matrix using xenon as the FAB gas. The low-resolution mass spectrum [12] ofindinavir is shown in Figure 14, while the structures of the structurally significant fragment ions are illustrated in Figure 15. 

Reproducibility of elution activity of Au-195m. A 2.5 x 1.3 cm heavily shielded Nal (Tl) detector with a 1 cm opening in the collimator was placed 20 cm from the outlet of the generator. This outlet was connected to the intravenous tubing inserted into an antecubital vein of the patient. The detector was connected to a spectrometer set at 260 keV with a 10% window. Three-second measurements were performed immediately after elution in groups of 6 elutions repeated every 3 min in each patient. 

The photograph presented in Figure 13.10 shows a typical interface used to collect these noninvasive spectra. Light is incident on one side of the skinfold and a fraction of the transmitted light is collected directly from across the input fiber. Bundles of low-hydroxy silica fibers are used to deliver and collect the near-infrared radiation for the measurement. For the experiments described here, the noninvasive spectra were collected with a Fourier transform spectrometer set for a resolution of 16 cm-1 and 128 coadded interferograms. Each recorded spectrum required approximately 60 s to acquire and save. A total of 370 spectra were collected over a period of nearly 7h while in vivo glucose concentrations varied from 6 to 33 mM (108-594 mg/dL). 

Figure 4.33 Definition of the energies and potentials relevant for the three-aperture lens shown in Fig. 4.32 at the entrance of an electron spectrometer. In this example electrons with kin = 2 eV emitted in the source volume which travel through the lens with electrodes L, L2) L3 and enter the spectrometer set at pass = 5 eV are shown. The potentials Vt on the electrodes can be given with respect to different reference values using the ordinate on the left-hand side one gets the actual potentials Vf at the electrodes, using the ordinate on the right-hand side one gets the values Vt used in the theoretical calculation (see equ. (4.47a)).

However, this approach is rather time consuming, and in many cases only the coincidence signals at the nominal spectrometer settings are of interest. The corresponding rate of true coincidences is then given by... 

The methyl derivative can be gas chromatographed and quantitated by a mass spectrometer set to monitor characteristic ions (m/e) of the compound (selective ion monitoring). ... 

Figure 2. Laser-excitation spectrum for nitric oxide in N2 flowing from burner at atmospheric pressure (spectrometer set for 0,0 y-band at 2262.0 A)...

The central idea in the laser-based method for detection of small quantities of H in restricted areas is that an intense laser strike can form a pothole in a metal. The metal of the pothole and the H it contains are vaporized. Both the H and some of the metallic atoms are withdrawn by a vacuum that pulls gaseous constituents out of the system. On the way, however, these constituents are made to fly through the space between the electrodes of a quadrupole mass spectrometer set to measure mass 2. Knowing the H2 produced from one laser strike, and the dimensions of the pothole, the H concentration in the metal—and within any restricted area to which the laser can be directed—can be measured. 

Adjust the spectrometer variables of spectral band pass, wavelength and lamp current according to the manufacturer s recommended conditions for Ni and V. It will be necessary to employ background correction for the determination with most electrothermal atomisers, especially in the case of Ni. Where available on the spectrometer, set up the deuterium or hydrogen lamp background correction system as recommended by the manufacturer. Otherwise use a nearby non-absorbing line to estimate the background intensity. 

The scattering cylinder of the focused laser beam must be aligned vertically to be parallel to the entrance slit of the spectrometer. The collection lens is used to image this cylinder onto the slit. The sample is then inserted at the laser focal point with its long axis parallel to the beam and a quick survey scan is taken until a Raman band is found. The sample, the excitation beam, and the collection lens are then carefully adjusted for maximum signal at this spectrometer setting. 

The duration of one measurement (1 element in a sample) may vary from a few seconds to several minutes. Where a analysis frequently carried out does not require any specific preparation (crushed sample, known matrix, calibration curve already stored and no new elements in the matrix of the sample), the duration of the analysis is 30 minutes (for calibration and checking of spectrometer settings) + 5 minutes per sample (two measurements per sample). 

Like scintillation detectors, semiconductor detectors are usually used in gamma spectrometer set-ups to identify radionuclides and determine their activities in a sample. A semiconductor detector is much more expensive and somewhat more troublesome to operate than a scintillation detector, but it can distinguish much better between different radiation energies and is better for nuclide identification. 

To determine these parameters accurately and rigorously, the experimental ESR spectrum should be compared to a computer-simulated spectrum calculated using trial parameters, and a convenient mathematical representation and description of the ESR spectrum should be provided by use of the operator spin Hamiltonian (Wertz and Bolton, 1972). In practice, the g-values and hyperline and superhyperfine constants, A, can be obtained relatively simply, although not rigorously, by direct computation from data derived accurately from the experimental ESR spectrum and from spectrometer setting values used in the measurement, according to conventional equations (Senesi, 1992). 

Analytical Methods for Urine and Blood. Specific biomarkers of lewisite exposure are currently based on a very limited number of in vitro experiments (Jakubowski et al., 1993 Wooten et al., 2002) and animal studies (Logan et al., 1999 Fidder et al., 2000). Wooten et al. (2002) developed a solid-phase microextraction (SPME) headspace sampling method for urine samples followed by GC-MS analysis. It is the most sensitive method reported to date with a lower limit of detection of 7.4 pg/mL. Animal experiments have been limited in number and in their scope. In one study of four animals, guinea pigs were given a subcutaneous dose of lewisite (0.5 mg/kg). Urine samples were analyzed for CVAA using both GC-MS and GC coupled with an atomic emission spectrometer set for elemental arsenic (Logan et al., 1999). The excretion profile indicated a very rapid elimination of CVAA in the urine. The mean concentrations detected were 3.5 pg/mL, 250 ng/mL, and 50 ng/mL for the 0-8, 8-16, and 16-24 h samples, respectively. Trace level concentrations... 

Figure 5. (c) The spectrometer, set in the nose cone of the rocket. Key /. entrance window for the polvchroniator and 2, entrance window for the triggering optical... 

Figure 14. Structure of the 5988.56-A line of neutral dysprosium (b) spectrum with mass spectrometer set to detect dysprosium-161 photoions (c) spectrum with mass spectrometer set to detect dysprosium-163 photoions (d) photoionization spectrum without mass selection. The strongest two peaks in (d) correspond to dysprosium-162 and dysprosium-164 transitions (11).

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