Light element quantification

Historically, EELS is one of the oldest spectroscopic techniques based ancillary to the transmission electron microscope. In the early 1940s the principle of atomic level excitation for light element detection capability was demonstrated by using EELS to measure C, N, and O. Unfortunately, at that time the instruments were limited by detection capabilities (film) and extremely poor vacuum levels, which caused severe contamination of the specimens. Twenty-five years later the experimental technique was revived with the advent of modern instrumentation. The basis for quantification and its development as an analytical tool followed in the mid 1970s. Recent reviews can be found in the works by Joy, Maher and Silcox " Colliex and the excellent books by Raether and Egerton. ... 

Rapp, A.O., Bestgen, H., Adam, W. and Peek, R.D. (1999). EELS (Electron Energy Loss Spectroscopy) a technique for the quantification of nitrogen and other light elements in the cell wall. International Research Group on Wood Preservation, Doc. No. IRG/WP 99-20163. 

Bastin GF, Heijligers HIM (1991) Quantitative electron probe microanalysis of ultra-light elements (boron-oxygen). In Electron Probe Quantification. KFJ Heinrich, Newbury DE (eds) Plenum Press, New York, p 145-151... 

The quantification of light elements (H, Li, and F) and, in particular, the direct knowledge of the chemical content of the anionic site plays a critical role in the assessment of the correct substitution mechanisms. In this regard, the measurement of the H content is of paramount importance, but it has to... 

Detail at the atomic level of spatial resolution concerning chemical states and composition is available from STM operated in its various modes—scanning Kelvin probe and scanning tunneling spectroscopy (STS) (Table 2). Single-atom resolution and site identification with these techniques are applicable only to reasonably conductive samples. The alternative is LEIS from which a combination of local atomic structure and quantification of surface composition, especially for light elements, can be obtained [14]. 

The quantification algorithm most commonly used in dc GD-OES depth profiling is based on the concept of emission yield [4.184], Ri] , according to the observation that the emitted light per sputtered mass unit (i. e. emission yield) is an almost matrix-independent constant for each element, if the source is operated under constant excitation conditions. In this approach the observed line intensity, /ijt, is described by the concentration, Ci, of element, i, in the sample, j, and by the sputtering rate g, ... 

In LC-ICP-MS, samples are separated on a chromatographic column, which may be a simple silica or alumina column with a relatively simple eluent. As the components elute from the column, they enter the ICP and the identity of the elements present and their concentration are determined based on the wavelengths of light (identity) and intensity of light (quantification) they emit. The exhaust from the ICP then enters the mass spectrometer, where the metals and their isotopic composition are determined based on their characteristic m/z ratios. The metals are thus identified and verified by two methods, ICP and MS [15]. 

The application of SIMS, SNMS, SSMS and GDMS in quantitative trace analysis for conducting bulk material is restricted to matrices where standard reference materials (SRMs) are available. For quantification purposes, the well characterized multi-element SRMs (e.g., from NIST) are useful. In Table 9.5 the results of the analysis by SNMS and the RSCs (relative sensitivity coefficients) for different elements in a low alloy steel standard (NBS 467) are compared with those of SSMS. Both solid-state mass spectrometric techniques with high vacuum ion sources allow the determination of light non-metals such as C, N, and P in steel, and the RSCs for the elements measured vary from 0.5 to 3 (except C). RSCs are applied as a correction factor in the analytical method used to obtain... 

Flame AFS combines features of both AAS and FES. The excitation of atoms is by the absorption of light. When individual element spectral line sources are used, the spectral selectivity should be as high as that in AAS, although scatter may be more of a problem in AFS. Quantification is by comparison of the intensity of fluorescence emitted by samples with that emitted by standards of known concentration. At low determinant concentrations, it is necessary to discriminate between small fluorescence emission signals and the background light levels associated with thermally excited emission from the flame. Therefore in AFS, as in FES, it is desirable to have low flame background emission. This is discussed further in Chapter 2, where instrumental aspects of flame spectrometric techniques are discussed. 

The quantification of elements by these two methods implies that a relation exists between the concentration and the intensity of the corresponding light absorption or emission. They make use of protocols which comprise a calibration curve from standard solutions of the analyte. 

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