Process atomic spectrometry

A large part of the success of the combination of FI and atomic spectrometry is due to its ability to overcome interference effects. The implementation of some pretreatment chemistry in the FI format makes it possible to separate the species of the analyte from the unwanted matrix species e.g. by converting each sample into a mixture of analyte(s) and a standard background matrix, designed not to interfere in the atom formation process and/or subsequent interaction with radiation in the atom cell). Often such separation procedures result also in an increased analyte mass flux into the atom source with subsequent improvements in sensitivity and detection limits. 

Capelo-Martinez, J.L., P. Ximenez-Embun, Y. Madrid, and C. Camara. 2004. Advanced oxidation processes for sample treatment in atomic spectrometry. Trends Anal. Chem. 23 331-340. 

The atomic/molecular weights of atoms or molecules in a mixture are determined with a mass spectrometer. The sample is vaporized, this gas is ionized, and these ions are deflected towards a magnet that separates them according to their mass. There are many specialized applications of mass spectrometry so there are dozens of variations to the process. Mass spectrometry is used to determine the ratio of 2H/1H in water, for 14C dating, and to characterize polymers and biological molecules with molecular weights of over a million. 

For rapid analysis during the production process atomic absorption is mainly of indirect value because, due to the sequential character of the technique, it cannot be used for complete steel or slag analysis in a two to three minute period. The analytical requirements for the testing of rapid continuous production processes are fulfilled by the techniques of emission and X-ray spectrometry. These techniques are characterised by great speed, high precision and simultaneous multi-element analysis. Accuracy must, however, be constantly checked with a variety of special calibration samples. This requires the determination of the true concentrations of the calibration samples with chemical methods of solution analysis, whose precision is often only equal to or, when compared with X-ray spectrometry, frequently poorer. Chemical analysis is, however, the basis of all comparisons, and must be repeated frequently for the determination of the true concentrations. Atomic absorption, with its relatively good precision, has greatly simplified the analytical control of numerous elements. 

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. 

Because of the necessity to characterize reference materials traceability in the measurements is very important. In atomic spectrometry background acquisition methods have improved so much that although it is not an absolute methodology, every step in the calibration and in the measurement processes can be extremely well characterized. 

Not only is there a need for the characterization of raw bulk materials but also the requirement for process controled industrial production introduced new demands. This was particularly the case in the metals industry, where production of steel became dependent on the speed with which the composition of the molten steel during converter processes could be controlled. After World War 11 this task was efficiently dealt with by atomic spectrometry, where the development and knowledge gained about suitable electrical discharges for this task fostered the growth of atomic spectrometry. Indeed, arcs and sparks were soon shown to be of use for analyte ablation and excitation of solid materials. The arc thus became a standard tool for the semi-quantitative analysis of powdered samples whereas spark emission spectrometry became a decisive technique for the direct analysis of metal samples. Other reduced pressure discharges, as known from atomic physics, had been shown to be powerful radiation sources and the same developments could be observed as reliable laser sources become available. Both were found to offer special advantages particularly for materials characterization. 

M.F. Gine, A.P. Packer, T. Blanco, B.F. Reis, Flow system based on a binary sampling process for automatic dilutions prior to flame atomic spectrometry, Anal. Chim. Acta 323 (1996) 47. 

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... 

Detailed description of all aspects of the application of atomic spectrometry to analysis of the huge variety of sample matrices associated with industrial processes is clearly outside the scope of this chapter and so only a brief overview is given of each application area. For detailed discussion of the application of atomic spectrometry in industrial analysis, the reader should refer to the annual reviews of this topic published in Atomic Spectrometry Updates in conjunction with J.Anal. At. Spec-trom., [3-12]. In Section 20.2, specific applications of atomic spectrometry to online/at-line analysis are discussed in more detail. 

As discussed above, atomic spectrometry plays a key role in the development, optimisation and efficient operation of most industrial processes. At the present time most of these appHcations are carried out using laboratory based analyses. In some cases the benefits of on-Hne analysis can be substantial, affording a much higher sampHng frequency, permitting tighter control of the process. Some progress has... 

Tables 20.4 to 20.8 summarize the use of atomic spectrometry in process control.

Argentine, M.D., Barnes, R.M. (1994) Electrothermal vaporization-inductively coupled plasma mass spectrometry for the analysis of semiconductor-grade organome-taUic materials and process chemicals. Journal of Analytical Atomic Spectrometry, 9,1371—1378. 

Wildner, H. (1998) Apphcation of inductively coupled plasma sector field mass spectrometry for the fast and sensitive determination and isotope ratio measurement of non-metals in high-purity process chemicals. Journal of Analytical Atomic Spectrometry, 13,573—578. 

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