Spectrochemical methods

Determination of the dissociation constants of acids and bases from the change of absorption spectra with pH. The spectrochemical method is particularly valuable for very weak bases, such as aromatic hydrocarbons and carbonyl compounds which require high concentrations of strong mineral acid in order to be converted into the conjugate acid to a measurable extent. 

The lines in the spectrum from any element always occur in the same positions relative to each other. When sufficient amounts of several elements are present in the source of radiation, each emits its characteristic spectrum this is the basis for qualitative analysis by the spectrochemical method. It is not necessary to examine and identify all the lines in the spectrum, because the strongest lines will be present in definite positions, and they serve to identify unequivocally the presence of the corresponding element. As the quantity of the element in the source is reduced, these lines are the last to disappear from the spectrum they have therefore been called the persistent lines or the rates ultimes (R.U. lines), and simplify greatly the qualitative examination of spectra. 

In this chapter, only atomic spectrochemical methods are discussed. Atomic spectra are line spectra, and are specific to the absorbing or emitting atoms (elements), i.e. the spectra contain information on the atomic structure. Each spectral line can be regarded as the difference between two atomic states ... 

Schoenfeld and Held [539] used a spectrochemical method to determine rubidium in seawater. They determined concentrations of rubidium in the range 0.008-0.04 p,g/ml in the presence of varying proportions and concentrations of other salts as internal standard. The coefficient of variation ranged from 7 to 25% for simulated seawater standards. 

As stated previously, spectrochemical methods of analysis involve the absorption and emission of light. Absorption is considered in Sections 7.4.1 to 7.4.3. Emission is considered in Section 7.4.4. 

Define spectrochemical methods, spectroscopy, spectrometry, spectrometer, and spectrophotometer. 

Scott, R.O., Mitchell, R.L., Purves, D. and Voss, R.C. (1971) Spectrochemical methods for the analysis of soils, plants and other agricultural materials. Bulletin 2. Macaulay Institute for Soil Research, Aberdeen, p. 8. 

One of the most challenging aspects of atomic spectrometry is the incredibly wide variety of sample types that require elemental analysis. Samples cover the gamut of solids, liquids, and gases. By the nature of most modem spectrochemical methods, the latter two states are much more readily presented to sources that operate at atmospheric pressure. The most widely used of these techniques are flame and graphite furnace atomic absorption spectrophotometry (FAAS and GF-AAS) [1,2] and inductively coupled plasma atomic emission and mass spectrometries (ICP-AES and MS) [3-5]. As described in other chapters of this volume, ICP-MS is the workhorse technique for the trace element analysis of samples in the solution phase—either those that are native liquids or solids that are subjected to some sort of dissolution procedure. 

USE OF SPECTROCHEMICAL METHODS FOR THE DETERMINATION OF METALS IN FISH AND OTHER SEAFOOD IN LOUISIANA... 

The most widely used spectrochemical methods are flame atomic absorption spectrometry (FAAS), electrothermal atomization atomic absorption spectrometry (ETA-AAS), and inductively coupled plasma atomic emission spectrometry (ICP-AES). Some work has been performed using inductively coupled plasma mass spectrometry (ICP-MS) and the unique properties of Hg have allowed the use of cold vapor (CV) A AS. It is beyond the scope of this chapter to describe these well-established and well-accepted spectrochemical techniques. The reader is referred to several excellent texts which describe in detail the basic principles, instrumentation, and method development of these analytical techniques [1-4]. The most toxic elements, such as As, Cd, Cr, Pb, and particularly Hg have been the most widely studied. Other metals, such as Ba, Cu, Fe, Mn, V, and Zn, have also been investigated. 

C. Th. J. Alkemade and P. J. Th. Zeegers, Spectrochemical Methods of Analysis Quantitative Analysis of Atoms and Molecules, Wiley, New York, 1971. 

The method of preparing the sample for assay depends upon the concentration of the element, the sensitivity of the spectrochemical procedure, and any interference phenomena arising from other constituents of the sample. In flame photometry, the sample is usually an aqueous solution, but in other methods it may be necessary to dry the sample on some form of support. With trace elements or micro samples, great care is needed to avoid contamination during sample collection and preparation. Frequently, elements are bound to protein or other organic matrices. As spectrochemical methods measure total element, sample preparation must be used to separate the metal into its various fractions. 

The standardization of spectrochemical procedures is difficult owing to the variety of material analyzed and the impossibility of producing a standard identical in composition to the sample. It is therefore necessary to determine the extent of interfering effects and to use a standard which will compensate for these. However, CV of better than 3% can readily be achieved with accuracies of the same order at the 0.1 /ig/ml or 10 g level. Spectrochemical methods of analysis are accurate and rapid when correctly used, but as the equipment becomes more complex, the operating procedure, quality control and the maintenance necessary to ensure reliability also becomes more elaborate. 

F8. Franklin, M. L., Horlick, G., and Malmstadt, H. V., Basic and practical considerations in utilising photon counting for quantitative spectrochemical methods. Anal. Chem. 41, 2-10 (1969). 

Spectroscopy has played a vital role in the development of modem atomic theory. In addition, spectrochemical methods have provided perhaps the most widely... 

Note that spectrochemical methods that use not only visible but also ultraviolet and infrared radiation are often called optical methods in spite of the fact that the human eye is sensitive to neither of the latter two types of radiation. This somewhat ambiguous terminology arises as a result of both the many common features of instruments for the three spectral regions and the similarities in the way in which we view the interactions of the three types of radiation with matter. 

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