Interferences in AAS

Spectral interferences in AAS arise mainly from overlap between the frequencies of a selected resonance line with lines emitted by some other element this arises because in practice a chosen line has in fact a finite bandwidth . Since in fact the line width of an absorption line is about 0.005 nm, only a few cases of spectral overlap between the emitted lines of a hollow cathode lamp and the absorption lines of metal atoms in flames have been reported. Table 21.3 includes some typical examples of spectral interferences which have been observed.47-50 However, most of these data relate to relatively minor resonance lines and the only interferences which occur with preferred resonance lines are with copper where europium at a concentration of about 150mgL 1 would interfere, and mercury where concentrations of cobalt higher than 200 mg L 1 would cause interference. 

Any difference in the behaviour of the analyte atoms in the sample and in the standard implies an interference. AAS using a line source for excitation suffers little spectral interference. Background interference in AAS is more important. This nonspecific absorption is caused by ... 

These are the only type of interference that do not require the presence of analyte. For AAS the problem of spectral interference is not very severe, and line overlap interferences are negligible. This is because the resolution is provided by the lock and key effect. To give spectral interference the lines must not merely be within the bandpass of the monochromator, but actually overlap each other s spectral profile (i.e. be within 0.01 nm). West [Analyst 99, 886, (1974)] has reviewed all the reported (and a number of other) spectral interferences in AAS. Most of them concern lines which would never be used for a real analysis, and his conclusion is that the only real problem is in the analysis of copper heavily contaminated with europium The most commonly used copper resonance line is 324.754 nm (characteristic concentration 0.1 pg cm- ) and this is overlapped by the europium 324.753 nm line (characteristic concentration 75 pg cm- ). 

This is by far the most frequently encountered interference in AAS. Basically, a chemical interference can be defined as anything that prevents or suppresses the formation of ground state atoms in the flame. A common example is the interference produced by aluminium, silicon and phosphorus in the determination of magnesium, calcium, strontium, barium and many other metals. This is due to the formation of aluminates, silicates and phosphates which, in many instances, are refractory in the analytical flame being used. 

The topic of interferences in AAS analyses is dealt with in Chapter 3 of this book. In general it is wise to take the precaution of checking for sample matrix interferences using the method of standard additions, to make general use of background correction techniques unless proven unnecessary, and to match closely the matrices of samples and standards. These precautions will limit the likelihood of errors due to a variety of potential interferences. 

The importance of interferences in AAS has been stressed (2). We have observed only chemical interferences for stained glass of medieval composition. The interference due to ionization of sodium, potassium. 

Interferences in AA spectroscopy are divided into spectral and nonspectral interferences. 

Spectral interferences in AAS arise mainly from overlap between the frequencies of a selected resonance line with lines emitted by some other element, which arises because in practice a chosen line has in fact a finite band-width . With flame emission spectroscopy, there is... 

Cu atoms that can absorb these lines. Therefore, there are few spectral interferences in AAS. The emitted spectrum consists of all the emission lines of the metal cathode, including many lines that are not resonance absorption lines, but these other lines do not interfere in the analysis. 

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... 

What causes chemical interference in AAS Give three examples. 

A generally useful and common approach to eliminate chemical interference in AAS is to use standard addition for quantitation. This will be described in more detail in the following section. 

Discuss why background correction is necessary in AA. Distinguish between physical and chemical interferences in AA. Explain what is meant by the term Smith Hieftje background correction and discuss how it differs from the kind of correction employed in the Perkin-Elmer Model 3110 AA. 

Spectral interferences in AAS due to direct overlapping of the emission lines from the primary radiation source and the adsorption line of another element in the atom cell are very rare. To give rise to a spectral interference, the lines must not merely be within the band pass of the monochromator, but must actually overlap with each other s spectral profile (i.e., be within 0.01 nm). Spectral interferences resulting from the overlap of molecular bands and lines are more of a problem in AAS. Examples of this type of interference are the nonspecific absorption at 217.0 nm which affects lead (e.g., sodium chloride gives a strong molecular absorption at this wavelength), and the calcium hydroxide absorption band on barium at 553.55 nm. Spectral interferences may usually be eliminated by the use of background correction. 

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. 

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