Interference atomic spectroscopy

Practically all classical methods of atomic spectroscopy are strongly influenced by interferences and matrix effects. Actually, very few analytical techniques are completely free of interferences. However, with atomic spectroscopy techniques, most of the common interferences have been studied and documented. Interferences are classified conveniently into four categories chemical, physical, background (scattering, absorption) and spectral. There are virtually no spectral interferences in FAAS some form of background correction is required. Matrix effects are more serious. Also GFAAS shows virtually no spectral interferences, but... 

Determination of trace metals in seawater represents one of the most challenging tasks in chemical analysis because the parts per billion (ppb) or sub-ppb levels of analyte are very susceptible to matrix interference from alkali or alkaline-earth metals and their associated counterions. For instance, the alkali metals tend to affect the atomisation and the ionisation equilibrium process in atomic spectroscopy, and the associated counterions such as the chloride ions might be preferentially adsorbed onto the electrode surface to give some undesirable electrochemical side reactions in voltammetric analysis. Thus, most current methods for seawater analysis employ some kind of analyte preconcentration along with matrix rejection techniques. These preconcentration techniques include coprecipitation, solvent extraction, column adsorption, electrodeposition, and Donnan dialysis. 

Thus, spectral interferences in atomic spectroscopy are less likely than in molecular spectroscopy analysis. In any case, even the atomic lines are not completely monochromatic i.e. only one wavelength per transition). In fact, there are several phenomena which also bring about a certain broadening . Therefore, any atomic line shows a profile (distribution of intensities) as a function of wavelength (or frequency). The analytical selectivity is conditioned by the overall broadening of the lines (particularly the form of the wings of such atomic lines). 

In atomic spectroscopy, absorption, emission, or fluorescence from gaseous atoms is measured. Liquids may be atomized by a plasma, a furnace, or a flame. Flame temperatures are usually in the range 2 300-3 400 K. The choice of fuel and oxidant determines the temperature of the flame and affects the extent of spectral, chemical, or ionization interference that will be encountered. Temperature instability affects atomization in atomic absorption and has an even larger effect on atomic emission, because the excited-state popula-... 

The besl isolation of radiant energy can he achieved with flame spectrometers that incorporate either a prism sir grating monochromator, those with prisms having variable gauged entrance and exii slits. Both these spectrometers provide a continuous selection of wavelengths with resolving power sufficient lo separate completely most of the easily excited emission lines, and afford freedom from scattered radiation sufficient lo minimize interferences. Fused silica or quartz optical components are necessary to permit measurements in Ihe ultraviolet portion of the spectrum below 350 nanometers Sec also Analysis (Chemical) Atomic Spectroscopy Photometers and Spectra Instruments. 

Marshall, J., and Franks, J. (1990) Multielement analysis and reduction of spectral interferences using electrothermal vaporization inductively coupled plasma-mass spectrometry. Atomic Spectroscopy 11, 177-186. 

It is obvious that HR-CS AAS will redefine not only AAS, but the entire field of atomic spectroscopy, as it combines the simplicity, ease of operation, relatively low cost and freedom from interferences of classical AAS with a number of features unavailable until now, or available only with much more sophisticated... 

As with all atomic spectroscopy techniques, ICP-MS also suffers from a number of interferences. 

Recently, flameless atomization techniques have been developed for atomic spectroscopy, particularly for atomic absorption. Absolute sensitivities of atomic absorption using these flameless atomizers are, for most elements, comparable with or better than those attainable by any other technique. Additionally, unlike most other techniques the atomic absorption method is relatively free from interferences by other components of the sample matrix. Therefore, flameless atomic absorption holds great promise for direct analysis of trace metals in seawater and other environmental samples. This paper reports the successful apphcation of a new design of commercial atomizer to direct analysis of several metals in seawater. 

In terms of the sample, specificity of the method is difficult to establish. It may be that the clean up procedure allows the final sample to be analysed free of interferences, but the process of obtaining such a laboratory sample from the original material in the environment has a great number of uncontrollable variables. Obvious interferents may be known and procedures adopted to avoid them. An example is the presence of high levels of sodium chloride in sea water samples, which proves difficult for atomic spectroscopy methods. 

Chemical deviations from Beer s iaw Deviations from Beer s law that result from association or dissociation of the absorbing species or reaction with the solvent, producing a product that absorbs differently from the analyte in atomic spectroscopy, chemical interactions of the analyte with interferents that affect the absorption properties of the analyte. 

Fernandez FJ, Giddings R. 1982. Elimination of spectral interference using Zeeman effect background correction. Atomic Spectroscopy 3 61-65. 

Sodium and potassium levels are difficult to analyze by titrimetric or colorimetric techniques but are among the elements most easily determined by atomic spectroscopy (2,38) (Table 2). Their analysis is important for the control of infusion and dialysis solutions, which must be carefully monitored to maintain proper electrolyte balance. Flame emission spectroscopy is the simplest and least expensive technique for this purpose, although the precision of the measurement may be improved by employing atomic absorption spectroscopy. Both methods are approved by the U.S. (39), British (40), and European (41) Pharmacopeias and are commonly utilized. Sensitivity is of no concern, due to the high concentrations in these solutions furthermore, dilution of the sample is often necessary in order to reduce the metal concentrations to the range where linear instmmental response can be achieved. Fortunately, the analysis may be carried but without additional sample preparation because other components, such as dextrose, do not interfere. 

When the solution sample is suitably diluted, usually in simple media, the analyte may be quantitated in seconds. Automation is widely and relatively inexpensively available. Atomic spectroscopy is inherently very specific and interferences that will reduce the bias below the level of the precision are few. Those interferences that exist are well characterized and are generally controlled in a routine manner. The net result of all this is that flame AAS should be used in every situation where it is applicable. 

It is apparent that the spectrophotometric procedures are rather time consuming since several multiple extractions must be performed in order to minimize interferences. Atomic absorption spectroscopy has enjoyed wide popularity in recent years as a trace metal analysis tool. This is due to a number of factors including high sensitivity, selectivity, and ease of sample preparation. With biological fluids, often no sample preparation at all is required, depending on the element analyzed, its concentration and the sample matrix. Because of its advantages, this technique will be treated in some detail. 

The development of atomic spectroscopic techniques and their appHcation to fundamental studies fostered the concurrent development of atomic theory and quantum mechanics. In turn, the better understanding of atomic theory has led to the implementation of many beneficial techniques and instrumental features in atomic spectroscopy, particularly for the reduction or elimination of interferences and background. 

To conclude our discussion on GFAA, as we did for ICP-AES, a calibration plot for the element Cr (as total chromium) is presented in Fig. 4.80 and is taken from the author s laboratory using the Model 310 (Perkin-Elmer) GFAA spectrophotometer. We also close our atomic spectroscopy discussion by summarizing in Table 4.21 the three major techniques to measure trace levels of metals from environmental samples and how to handle interferences. We now turn to two remaining determinative techniques of relevance to TEQA, infrared absorption spectroscopy, and capillary electrophoresis. 

The chapters in the book that deal with the methods of atomic spectroscopy discuss such things as the basic principles involved in the method, the instrumentation requirements, variations of instrumentation, advantages and disadvantages of the method, problems of interferences, detection limits, the collection and processing of the data, and possible applications. Since the book is intended to serve as a textbook, principles are stressed. Detailed methods of analysis for specific elements are not included. It is the hope of the author, however, that the presentation of basic information is sufficiently detailed so the students can develop their own methods of analysis as needed. 

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