Spectrum spark

Qualitatively, the spark source mass spectrum is relatively simple and easy to interpret. Most instrumentation has been designed to operate with a mass resolution Al/dM of about 1500. For example, at mass M= 60 a difference of 0.04 amu can be resolved. This is sufficient for the separation of most hydrocarbons from metals of the same nominal mass and for precise mass determinations to identify most species. Each exposure, as described earlier and shown in Figure 2, covers the mass range from Be to U, with the elemental isotopic patterns clearly resolved for positive identification. 

The spark source is an energetic ionization process, producing a rich spectrum of multiply charged species (Af/2, Af/3, Af/4, etc.). These masses, falling at halves, thirds, and fourths of the unit mass separation can aid in the positive identification of elements. In Figure 2, species like Au and are labeled. The most abundant... 

Approximately 70 different elements are routinely determined using ICP-OES. Detection limits are typically in the sub-part-per-billion (sub-ppb) to 0.1 part-per-million (ppm) range. ICP-OES is most commonly used for bulk analysis of liquid samples or solids dissolved in liquids. Special sample introduction techniques, such as spark discharge or laser ablation, allow the analysis of surfaces or thin films. Each element emits a characteristic spectrum in the ultraviolet and visible region. The light intensity at one of the characteristic wavelengths is proportional to the concentration of that element in the sample. 

Gallium was predicted as eka-aluminium by D. 1. Mendeleev in 1870 and was discovered by P. E. Lecoq de Boisbaudran in 1875 by means of the spectroscope de Boi.sbaudran was, in fact, guided at the time by an independent theory of his own and had been searching for the missing element for some years. The first indications came with the observation of two new violet lines in the spark spectrum of a sample deposited on zinc, and within a month he had isolated 1 g of the metal starting from several hundred kilograms of crude zinc blende ore. The... 

The glow was blue in color and changed to the ordinary yellow-green glow with continuous spectrum if the spark gap was excluded. The spectrum of the glow was photographed with a small Hilger quartz spectro-... 

Thorne, R. P. The. Spark Spectrum of Americium. Spectrochim. Acta 8, 71... 

Harrison GR (1939) M. I. T. wave-length tables with intensities in arc, spark or discharge tube of more than 100,000 spectrum lines. Wiley, New York... 

The spectrum of tin emitted from a triggered spark source in the far UV region (17.5-200 nm) has been analysed26. The emission lines in this region may be useful for development of new analytical methods. 

The basic instrumentation used for spectrometric measurements has already been described in the previous chapter (p. 277). Methods of excitation, monochromators and detectors used in atomic emission and absorption techniques are included in Table 8.1. Sources of radiation physically separated from the sample are required for atomic absorption, atomic fluorescence and X-ray fluorescence spectrometry (cf. molecular absorption spectrometry), whereas in flame photometry, arc/spark and plasma emission techniques, the sample is excited directly by thermal means. Diffraction gratings or prism monochromators are used for dispersion in all the techniques including X-ray fluorescence where a single crystal of appropriate lattice dimensions acts as a grating. Atomic fluorescence spectra are sufficiently simple to allow the use of an interference filter in many instances. Photomultiplier detectors are used in every technique except X-ray fluorescence where proportional counting or scintillation devices are employed. Photographic recording of a complete spectrum facilitates qualitative analysis by optical emission spectrometry, but is now rarely used. 

A rather specialized emission source, which is applicable to the study of small samples or localized areas on a larger one, is the laser microprobe. A pulsed ruby laser beam is focused onto the surface of the sample to produce a signal from a localized area ca. 50 pm in diameter. The spectrum produced is similar to that produced by arc/spark sources and is processed by similar optical systems. 

Compared to flame excitation, random fluctuations in the intensity of emitted radiation from samples excited by arc and spark discharges are considerable. For this reason instantaneous measurements are not sufficiently reliable for analytical purposes and it is necessary to measure integrated intensities over periods of up to several minutes. Modern instruments will be computer controlled and fitted with VDUs. Computer-based data handling will enable qualitative analysis by sequential examination of the spectrum for elemental lines. Peak integration may be used for quantitative analysis and peak overlay routines for comparisons with standard spectra, detection of interferences and their correction (Figure 8.4). Alternatively an instrument fitted with a poly-chromator and which has a number of fixed channels (ca. 30) enables simultaneous measurements to be made. Such instruments are called direct reading spectrometers. 

Problems may arise from the different volatility of elements in the sample which will in turn be modified by the matrix. Fractional distillation can occur and a serious error result unless the sample is completely burned, because the emission intensity for each element will vary independently with time (Figure 8.5(a)). On the other hand, this effect may well be exploited as in the case of volatile impurities in a non-volatile matrix. By recording the spectrum only in the early part of a bum, they may be detected with little interference from the matrix. The pre-spark routine discussed earlier (p. 290) may also be used to improve precision. 

The original OES instruments, dating from the 1930s but used consistently from the 1950s, used a spark source to excite the emission spectrum, which usually consisted of a graphite cup as one electrode, and a graphite rod as the other. The sample (solid or liquid) was placed inside the cup and the graphite rod lowered until it was close to the cup. The sample was then vaporized by... 

A recent modification of mass spectrometric technique involves the use of a spark source. A spark is struck by means of a high voltage between two rods of the material under examination. Under this drastic treatment many substances decompose completely into their elements and give positive ions. The ion detector is usually a photographic plate which shows a line mass spectrum. A number of exposures are taken for each sample and a quantitative estimate of the presence of an element in the sample can be made from the exposure time. 

The optical emission spectrum of technetium is uniquely characteristic of the element " with a few strong lines relatively widely spaced as in the spectra of manganese, molybdenum and rhenium. Twenty-five lines are observed in the arc and spark spectra between 2200 and 9000 A. Many of these lines are free from ruthenium or rhenium interferences and are therefore useful analytically. Using the resonance lines of Tc-I at 4297.06, 4262.26, 4238.19, and 4031.63 A as little as 0.1 ng of technetium can be reliably determined. 

Thus, although the colour of sparks is dependent upon flame temperature and may be similar to that of black body radiation, the overall colour effect can include contributions from atomic line emissions, from metals (seen in the UV and visible regions of the electromagnetic spectrum), from band emissions from excited oxide molecules (seen in the UV, visible and IR regions) and from continuum hot body radiation and other luminescence effects. So far as black body radiation is concerned, the colour is known to change from red (500 °C glowing cooker... 

Promethium is identified by x-ray emission spectra, spark spectrum, and other spectroscopic methods. At extremely low concentrations, the element can be measured by ICP-MS. Also promethium and its salts can be detected from their pale—blue or greenish glow in the dark due to their radioactivity. Highly sensitive beta probes can be used for monitoring radioactive Pm-147. 

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