Methods of elemental analysis

Walsh, A. The Development of Atomic Absorption Methods of Elemental Analysis 1952-1962, Anal Chem. 1991, 63, 933A-941A. 

Sample prepai ation is a limited stage of the analytieal proeess taking about 90 % time of praetieally any method of element analysis for determination of both basie substanees and admixtures. The intensifieation of sample prepai ation stage is one of the important problems in analytieal praetiee. For the deeision of this problem we offer use of the eombined ehemieal and physieal influenees on a number of proeesses of a sample prepai ation stage (deeomposition, eoneentrating, separating ete.). 

In summary, there is relatively good agreement overall between different methods of elemental analysis for atmospheric particles, with many of the observed dis-... 

It is a method of elemental analysis for various practical reasons and it is essentially suitable for analysis only of metals. A large number of elements can be analyzed for at trace levels. Therefore, its biotechnologic applications mainly involve in measurement of inorganic elements such as alkali, trace, and heavy metals in biological investigations. It is also used in industry to monitor contaminating inorganic elements in bioreactors fermentation process and preparation of culture media. 

The principle behind these two methods of elemental analysis depends on measurements made on an analyte that is transformed into free atoms. To this end, for both techniques, the sample is heated in the instrument to a temperature of between 2000 and 3 000 degrees to break chemical bonds, liberate the elements present and transform them into a gaseous atomic state. Thus, the total concentration of the element is measured without distinguishing the chemical structures present in the cold sample. 

X-ray fluorescence spectrometry (XRF) is a non-destructive method of elemental analysis. XRF is based on the principle that each element emits its own characteristic X-ray line spectrum. When an X-ray beam impinges on a target element, orbital electrons are ejected. The resulting vacancies or holes in the inner shells are filled by outer shell electrons. During this process, energy is released in the form of secondary X-rays known as fluorescence. The energy of the emitted X-ray photon is dependent upon the distribution of electrons in the excited atom. Since every element has a unique electron distribution, every element produces... 

One of the biggest advantages of XRF over other methods of elemental analysis is that it is nondestructive and requires minimal sample preparation. WDXRF, when properly calibrated, offers precision and accuracy comparable to wet chemical methods of analysis. EDXRF offers rapid qualitative analysis of total unknowns. 

Nadkarni, R.A., Ed., Modern Instrumental Methods of Elemental Analysis of Petroleum Products and Lubricants, ASTM, STP 1109, Philadelphia, PA, 1991. 

For many methods of elemental analysis, the organic constituents of plant material are eliminated either by dry ashing or by wet digestion (Sulcek and Povondra, 1989). Stoeppler (1991) has summarised the most frequently used decomposition methods for trace and ultratrace analysis of biological and environmental materials. 

The usefulness of the ICP technique in elemental analysis was demonstrated by the pioneering work of Greenfield et al. (1964) and Wendth and Fassel (1965). The technique has been developed and refined and is the most rapidly growing method of elemental analysis. The ICP source is based on the inductive heating of a gas flowing in a tube assembly (torch) and is operated at frequencies between 1 and 100 MHz. 

Either fusion with alkali metals or reaction with aUcali-metal complexes with aromatic hydrocarbons will break down most fluorocarbon systems, due to the high electron affinities of these systems. Such reactions form the basis of some methods of elemental analysis [13], the fluorine being estimated as hydrogen fluoride after ion exchange. Surface defluorination of PTFE occurs with alkali metals and using other techniques [14]. Per-fluorocycloalkanes give aromatic compounds by passage over hot iron and this provides a potential route to a variety of perfluoroaromatic systems (Chapter 9, Section IB). 

Atomic absorption spectrometry is a method of elemental analysis which exploits the property of atoms of being excited by external energy in the form of electromagnetic radiation (photons) with well defined frequencies. 

The instrumental methods of elemental analysis can be conveniently grouped as follows ... 

The following instrumental methods of elemental analysis are based on X-ray spectrometry. 

Radio frequency-powered GD sources have been coupled with various analytical spectrometries for more than two decades [167]. Analyses are not limited to conducting samples in fact, electrical insulators such as glass, ceramics and geological materials — some of the most difficult samples to dissolve for solution methods of elemental analysis — can be readily examined. 

The different methods of AAS and also the related CFS are very powerful for the analysis of solutions. The instruments are simple and easy to operate. Accordingly, they are now used in almost all analytical laboratories. In particular, when one or only a few elements have to be determined in a large number of samples, as is e.g. the case in clinical analysis or in food analysis, AAS methods are of great use as compared with other methods of elemental analysis. 

The purpose of this section is to provide a brief review of the methods and techniques commonly used in the elemental analysis of humic substances with special emphasis placed on areas that may cause difficulties in their analysis. There are few specific references to methods of elemental analysis of humic substances. A computerized search of Chemical Abstracts since 1966 revealed no references to techniques of elemental analysis when elemental analysis was cross-referenced with humic or fulvic acid materials. In general, the methods of analysis have been developed to be applicable to a wide range of organic materials. However, it should be pointed out that most methods have been validated on the basis of the analysis of stable, nonhy-groscopic, nonvolatile, pure compounds and not heterogeneous mixtures. 

For more details on these methods, there is a variety of references that may be consulted. The classical methods are given by Pregl (1930) and Niederl and Niederl (1938). Steyermark (1961) and Ingram (1962) have rather thoroughly presented the noninstrumental methods of elemental analysis. The more recent methods, especially the instrumental methods, have been presented in books by Ehrenberger and Gorbach (1973), Belcher (1977), Ma and Rittner (1979), Bance (1980), and Kirsten (1983). Multivolume series such as the Treatise on Analytical Chemistry (Kolthoff and Elving 1959-1981) and Comprehensive Analytical Chemistry (Wilson and Wilson, 1959)... 

Traditional methods of elemental analysis depend on specific chemical reactions for given elements, either in solution using titrations (known as volumetric analysis) or precipitation of solids that can be weighed (gravimetric analysis). Although such methods are still used for specific and very accurate purposes, they have been replaced in routine work by automated instrumental methods. Combustion analysis is used to determine C, H, N, and sometimes S, by complete oxidation of the compound forming C02, H20, N2 and S02. The gases are separated and determined automatically... 

Figure 13.18 Elements measured by AAS and FES. Most elements can be measured by atomic absorption or flame emission by using one of the available modes of atomization (burner, graphite furnace or device for hydride formation). The sensitivity varies from several ppb (Cu, Cd, Cr) to several ppm (the lanthanides). The elements of the table (in white) for which the atomic number is not shown are not measurable by atomic absorption. However, the hybrid apparatus AAS/OES containing plasmas as a thermal source, has more recently pushed back the limits of this method of elemental analysis.

Rapidity and detection limits below 1 ppb (10 ) for many elements, make OES one of the best methods of elemental analysis. With instruments containing one array detector it is possible to record in a few seconds the whole spectrum in high resolution (e.g. several thousands emission spectral lines). 

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