Dispersive spectrometry

The rapidity with which information is received one second instead of an average 10 minutes for dispersive spectrometry. 

To examine a sample by inductively coupled plasma mass spectrometry (ICP/MS) or inductively coupled plasma atomic-emission spectroscopy (ICP/AES) the sample must be transported into the flame of a plasma torch. Once in the flame, sample molecules are literally ripped apart to form ions of their constituent elements. These fragmentation and ionization processes are described in Chapters 6 and 14. To introduce samples into the center of the (plasma) flame, they must be transported there as gases, as finely dispersed droplets of a solution, or as fine particulate matter. The various methods of sample introduction are described here in three parts — A, B, and C Chapters 15, 16, and 17 — to cover gases, solutions (liquids), and solids. Some types of sample inlets are multipurpose and can be used with gases and liquids or with liquids and solids, but others have been designed specifically for only one kind of analysis. However, the principles governing the operation of inlet systems fall into a small number of categories. This chapter discusses specifically substances that are normally liquids at ambient temperatures. This sort of inlet is the commonest in analytical work. 

There is potential confusion in the use of the word array in mass spectrometry. Historically, array has been used to describe an assemblage of small single-point ion detectors (elements), each of which acts as a separate ion current generator. Thus, arrival of ions in one of the array elements generates an ion current specifically from that element. An ion of any given m/z value is collected by one of the elements of the array. An ion of different m/z value is collected by another element. Ions of different m/z value are dispersed in space over the face of the array, and the ions are detected by m/z value at different elements (Figure 30.4). 

Chemical analysis of the metal can serve various purposes. For the determination of the metal-alloy composition, a variety of techniques has been used. In the past, wet-chemical analysis was often employed, but the significant size of the sample needed was a primary drawback. Nondestmctive, energy-dispersive x-ray fluorescence spectrometry is often used when no high precision is needed. However, this technique only allows a surface analysis, and significant surface phenomena such as preferential enrichments and depletions, which often occur in objects having a burial history, can cause serious errors. For more precise quantitative analyses samples have to be removed from below the surface to be analyzed by means of atomic absorption (82), spectrographic techniques (78,83), etc. 

Elemental chemical analysis provides information regarding the formulation and coloring oxides of glazes and glasses. Energy-dispersive x-ray fluorescence spectrometry is very convenient. However, using this technique the analysis for elements of low atomic numbers is quite difficult, even when vacuum or helium paths are used. The electron-beam microprobe has proven to be an extremely useful tool for this purpose (106). Emission spectroscopy and activation analysis have also been appHed successfully in these studies (101). 

POSSIBILITY OF USING GRASING EMISSION IN WAVE DISPERSION X-RAY SPECTROMETRIES... 

These samples were measured non-destructively by energy-dispersive XRF with synclirotron radiation excitation (SYXRS), by g-XRF, by wavelength-dispersive XRF (WDXRS), and by Rutherford back scattering (RBS), by X-ray reflectometry (XRR) and by destructive secondary ion mass spectrometry (SIMS) as well (both last methods were used for independant comparison). 

The electron-optical performance of the EPMA system is indistinguishable from that of a conventional scanning electron microscope (SEM) thus, EPMA combines all of the imaging capabilities of a SEM with quantitative elemental analysis using both energy- and wavelength-dispersive X-ray spectrometry. ... 

The analyst has two practical means of measuring the energy distribution of X rays emitted from the specimen energy-dispersive spectrometry and wavelength dispersive spectrometry. These two spectrometers are highly complementary the strengths of each compensate for the weaknesses of the other, and a well-equipped electron probe instrument will have both spectrometers. 

FCC feedstocks contain sulfur in the form of organic-sulfur compounds such as mercaptan, sulfide, and thiophenes. Frequently, as the residue content of crude oil increases, so does the sulfur content (Table 2-5). Total sulfur in FCC feed is determined by the wavelength dispersive x-ray fluorescence spectrometry method (ASTM D-2622), The results are expressed as elemental sulfur. 

Analyses of gases and vapours tend to utilize the techniques described on page 308. Many of these methods were traditionally limited to laboratory analyses but some portable instruments are now available for, e.g., gas chromatography (Table 10.16) and non-dispersive infra-red spectrometry (Table 10.17). 

Laser Ablation ICP Optical Emission Spectrometry ICP Mass Spectrometry Transmission Electron Microscopy with Energy-Dispersive X-Ray Analysis... 

Taggart JE Jr, Lindsay JR, Scott BA, Vivit DV, Bartel AJ, Stewart K C (1993) Analysis of geological materials by wavelength-dispersive X-ray fluorescence spectrometry. In Badecker PA, ed. U.S. Geological Survey Bulletin 1770. Methods for Geochemical Analysis, pp E1-E19. 

H. Vare, Aluminum polyphosphate in the ectomycorrhizal fungus Siiillus variega-tiis (Fr.) O. Kuntze as revealed by energy dispersive spectrometry. New Phytol. 7/6 663 (1990). 

Depending on how the secondary magnetic field is applied, there are two fundamentally different types of spectrometers, namely, continuous wave (CW) and pulse Fourier transform (PFT) spectrometers. The older continuous wave NMR spectrometers (the equivalent of dispersive spectrometry) were operated in one of two modes (i) fixed magnetic field strength and frequency (vi) sweeping of Bi irradiation or (ii) fixed irradiation frequency and variable field strength. In this way, when the resonance condition is reached for a particular type of nuclei (vi = vo), the energy is absorbed and... 

ToF analysers are able to provide simultaneous detection of all masses of the same polarity. In principle, the mass range is not limited. Time-of-flight mass analysis is more than an alternative method of mass dispersion it has several special qualities which makes it particularly well suited for applications in a number of important areas of mass spectrometry. These qualities are fast response time, compatibility with pulsed ionisation events (producing a complete spectrum for each event) ability to produce a snapshot of the contents of the source volume on the millisecond time-scale ability to produce thousands of spectra per second and the high fraction of the mass analysis cycle during which sample ions can be generated or collected. 

Table 8.38 Main features of wavelength-dispersive X-ray fluorescence spectrometry (WDXRF)...

Energy-dispersive spectrometry (EDS) is a technique of X-ray spectroscopy that is based on the simultaneous collection and energy dispersion of characteristic X-rays. Typical ED detectors are thermoelectrically cooled semiconductors (usually operated at 77 K), PIN diodes,... 

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