Spectral interferences optical spectrometry

BeryUium aUoys ate usuaUy analyzed by optical emission or atomic absorption spectrophotometry. Low voltage spark emission spectrometry is used for the analysis of most copper-beryUium aUoys. Spectral interferences, other inter-element effects, metaUurgical effects, and sample inhomogeneity can degrade accuracy and precision and must be considered when constmcting a method (17). 

In optical emission and in mass spectrometry, spectral interferences remain an important limitation to the analytical accuracy achievable. In atomic emission this applies particularly to the heavier elements as they have the more line rich atomic spectra. When these heavy metals are present as the matrix, as is often the case in metal analysis, the necessitity of matrix separations is obvious when trace analyses... 

Inductively coupled plasma (ICP) ionization has currently assumed a more prominent role in the field of elemental and isotopic analysis [1,2,14]. It is apphcable to solid-state as well as to solution-phase samples. A plasma is defined as a form of matter that contains a significant concentration of ions and electrons. The heart of this technique is a plasma torch, first developed as an efficient source for optical emission spectroscopy (OES) [15,16]. Multielement analysis with OES has, however, some serious shortcomings, such as complicated spectra, spectral interferences, high background levels, and inadequate detection of some rare-earth and heavy elements. The high ionization efficiency (>90%) of ICP for most elements is an attractive feature for its coupling to mass spectrometry. 

Use of a collision cell. Another novel approach to eliminating isobaric spectral interferences is to nse a collision cell [21]. A collision cell approach is similar to the fragmentation scheme used in tandem mass spectrometry. An rf-only multipole collision ceU is positioned between the ion extraction optics and the mass analyzer and is filled with hydrogen or helium as a collision gas. Polyatomic interfering species, such as Ar", Ar 0", and ArH+, are converted to nentral species or noninterfering ionic species, and thns are shifted away from the m/z of the analyte. 

ICP optical emission spectrometry (ICP-OES) is also well established, and numerous procedures exist for a host of complex sample types. It is not uncommon to employ internal standards for ICP-OES. This is particularly useful to compensate partially for variations in sample delivery rate and, to a lesser extent, for small fluctuations in the plasma. The technique is relatively free of chemical interferences, and most spectral interferences can be corrected for. In addition to providing parts per billion to parts per million limits of detection for most of the periodic table with precisions of a few per cent or less, ICP-OES can also provide five to six orders of magnitude in analytical dynamic range. 

Interferences are physical or chemical processes that cause the signal from the analyte in the sample to be higher or lower than the signal from an equivalent standard. Interferences can therefore cause positive or negative errors in quantitative analysis. There are two major classes of interferences in AAS, spectral interferences and nonspectral interferences. Nonspectral interferences are those that affect the formation of analyte free atoms. Nonspectral interferences include chemical interference, ionization interference, and solvent effects (or matrix interference). Spectral interferences cause the amount of light absorbed to be erroneously high due to absorption by a species other than the analyte atom. While all techniques suffer from interferences to some extent, AAS is much less prone to spectral interferences and nonspectral interferences than atomic anission spectrometry and X-ray fluorescence (XRF), the other major optical atomic spectroscopic techniques. 

The analytical accuracy of methods can only be discussed in view of the complete analytical procedure applied. It is necessary to tune sample preparation and trace-matrix separations to the requirements of the analytical results in terms of accuracy, power of detection, precision, cost, number of elements, and, increasingly, the species to be determined. However, the intrinsic sensitivity of the different determination methods to matrix interference remains important. In optical emission and mass spectrometry, spectral interference remains an important limitation to the achievable analytical accuracy. In atomic emission, this applies especially to the heavier elements, as they have the more complex atomic spectra. Especially when they are present as the... 

Boumans, P. W. J. M., Con ctions for Spectral Interferences in Optical Emission Spectrometry with Special Reference to the RF Inductively Coupled Plasma," Specirochimlca Acta, 1976, Vol 3IB, pp. 147-1S2. 

---