Spectrometry optical atomic

Atomic spectroscopic methods are used for the qualitative and quantitative determination of more than 70 elements. Typically, these methods can detect parts-per-million to parts-per-billion amounts, and, in some cases, even smaller concentrations. Atomic spectroscopic methods are, in addition, rapid, convenient, and usually of high selectivity. They can be divided into two groups optical atomic spectrometry and atomic mass spectrometry. ... 

The basic processes in optical atomic spectrometry involve the outer electrons of the atomic species and therefore its possibilities and limitations can be well understood from the theory of atomic structure itself. On the other hand, the availability of optical spectra was decisive in the development of the theory of atomic structure and even for the discovery of a series of elements. With the study of the relationship between the wavelengths of the chemical elements in the mid-19th century a fundament was obtained for the relationship between the atomic structure and the optical line emission spectra of the elements. 

Owing to the line broadening mechanisms, the physical widths of spectral lines in most radiation sources used in optical atomic spectrometry are between 1 and 20 pm. This applies both for atomic emission and atomic absorption line profiles. In reality the spectral bandwidth of dispersive spectrometers is much larger than the physical widths of the atomic spectral lines. 

Atomic spectrometric methods of analysis essentially make use of equipment for spectral dispersion so as to isolate the signals of the elements to be determined and to make the full selectivity of the methodology available. In optical atomic spectrometry, this involves the use of dispersive as well as of non-dispersive spectrometers. The radiation from the spectrochemical radiation sources or the radiation which has passed through the atom reservoir is then imaged into an optical spectrometer. In the case of atomic spectrometry, when using a plasma as an ion source, mass spectrometric equipment is required so as to separate the ions of the different analytes according to their mass to charge ratio. In both cases suitable data acquisition and data treatment systems need to be provided with the instruments as well. 

In optical atomic spectrometry the radiation emitted by the radiation source or the radiation which comes from the primary source and has passed through the atom reservoir has to be lead into a spectrometer. In order to make optimum use of the source, the radiation should be lead as complete as possible into the spectrometer. The amount of radiation passing through an optical system is expressed by its optical conductance. Its geometrical value is given by ... 

Whereas in optical atomic spectrometry photographic emulsions are now rarely used, they are made use of in mass spectrometry with spark sources in particular. Here they are very useful for survey semi-quantitative analyses, and they still are of great importance for routine high-purity metals analysis and semiconductor material analysis. 

These two-dimensional detectors [63] are ideally suited for coupling with an echelle spectrometer, which is state of the art in modem spectrometers for ICP atomic emission spectrometry as well as for atomic absorption spectrometers. As for CCDs the sensitivity is high and along with the signal-to-noise ratios achievable, they have become real alternatives to photomultipliers for optical atomic spectrometry (Table 3) and will replace them more and more. 

As in the sources used in optical atomic spectrometry a considerable ionization takes place, they are also of use as ion sources for mass spectrometry. Although an overall treatment of instrumentation for mass spectrometry is given in other textbooks [68], the most common types of mass spectrometers will be briefly outlined here. In particular, the new types of elemental mass spectrometry sources have to be considered, namely the glow discharges and the inductively and eventually the microwave plasmas. In contrast with classical high voltage spark mass spectrometry (for a review see Ref. [69]) or thermionic mass spectrometry (see e.g. Ref. [70]), the plasma sources mentioned are operated at a pressure which is considerably... 

MicroChannel plate detectors can also be used. When using a phosphor, the detector can be coupled with photodiode arrays or charge coupled devices, which are known from optical atomic spectrometry, and it becomes possible to detect ions of different masses simultaneously as in the case of photoplate detection. 

The achievable ablation rates depend on the sample composition, the discharge gas and its pressure. As a filler gas a noble gas is normally used. Indeed, in the case of nitrogen or oxygen, chemical reactions at the sample surface would occur and disturb the sputtering, as electrically non-conductive oxide or nitride layers would be formed. Furthermore, reactions with the ablated material would produce molecular species, which emit molecular band spectra in optical atomic spectrometry or produce cluster ion signals in mass spectrometry. In both cases severe spectral in-... 

In the course of the late 1970s new mass spectrometric methods, which made use of the plasma sources known from optical atomic spectrometry came into use. They will be treated in detail and consist in particular of ICP mass spectrometry (ICP-MS) and glow discharge mass spectrometry (GD-MS), which have contributed to a considerable portion of the progress that has been made in elemental analysis as compared with spark source mass spectrometry. 

Atomic Absorption Spectrometry (Optical Atomic Spectrometry)... 

Atomic absorption spectrometry, belonging to a class of techniques also defined as optical atomic spectrometry, has been for some four decades - and continues to be - one of the most important, dominant determinative techniques. It includes flame atomic absorption spectrometry (FAAS), electrothermal atomization atomic absorption spectrometry (ETAAS) (including graphite furnace AAS (GFAAS), carbon rod AAS, tantalum strip AAS), and gaseous generation (cold vapor AAS for Hg, hydride gener-... 

OAS optical atomic spectrometry obstipation severe constipation OECD Organisation for Economic Cooperation and Development OES optical emission spectrometry OES-DCP See DCP-AES OES-ICP See ICP-AES OES-MIP See MIP-AES oliguria pathologically diminished excretion of urine... 

For all the techniques of optical atomic spectrometry, the samples (solutions and/or solid samples) must be converted into an atomic vapour. The sensitivity is strongly dependent on the yield of this process, as are the chemical and physical interferences, i.e. the specificity of the method in general. For the first approach, the atomization of the sample is proportional and the occurrence of chemical and/or physical interferences is inversely proportional to the excitation temperature. Therefore the temperature available in the atomization stage should be as high as possible. The classical excitation sources used in atomic spectrometry like flame, graphite furnace, arc and spark are well known. The temperature available, especially in a flame or in the graphite furnace, is around 3000°C. Due to the Boltzmann-distribution... 

In this section, we briefly con.sider the theoretical basis of optical atomic spectrometry and some of the important characterislies of optical spectra. 

In the course of the late 1970s new mass spectrometric methods, which made use of the plasma sources known from optical atomic spectrometry came into use. 

The sources used for optical atomic spectrometry are also powerful sources for elemental mass spectrometry, from the classical spark source mass spectrometer to present-day plasma mass spectro-metric methods such as glow discharge and inductively coupled plasma mass spectrometry. 

Atomic spectrometric methods of analysis essentially make use of equipment for spectral dispersion to achieve their selectivity. In optical atomic spectrometry, this involves the use of dispersive as well as nondispersive spectrometers, whereas in the case of atomic spectrometry with plasma ion sources mass spectrometric equipment is used. In both cases, suitable data acquisition and processing systems are built into the instruments. 

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