Atomic spectrometry spectral interferences

Spectral interference is rarely encountered in atomic absorption spectrometry. Spectral interferences in the past were experienced typically if, in a given solution, element A was being determined in the presence of element... 

In atomic fluorescence spectrometry spectral interferences are low as the fluorescence spectra are not line rich. 

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... 

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... 

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). 

Boumans PWJM (1994) Detection limits and spectral interferences in atomic emission spectrometry. Anal Chem 66 459A... 

Flame emission spectrometry is used extensively for the determination of trace metals in solution and in particular the alkali and alkaline earth metals. The most notable applications are the determinations of Na, K, Ca and Mg in body fluids and other biological samples for clinical diagnosis. Simple filter instruments generally provide adequate resolution for this type of analysis. The same elements, together with B, Fe, Cu and Mn, are important constituents of soils and fertilizers and the technique is therefore also useful for the analysis of agricultural materials. Although many other trace metals can be determined in a variety of matrices, there has been a preference for the use of atomic absorption spectrometry because variations in flame temperature are much less critical and spectral interference is negligible. Detection limits for flame emission techniques are comparable to those for atomic absorption, i.e. from < 0.01 to 10 ppm (Table 8.6). Flame emission spectrometry complements atomic absorption spectrometry because it operates most effectively for elements which are easily ionized, whilst atomic absorption methods demand a minimum of ionization (Table 8.7). 

D. C. Baxter and J. Ohman, Multi-component standard additions and partial least squares modelling, a multivariate calibration approach to the resolution of spectral interferences in graphite furnace atomic absorption spectrometry, Spectrochim. Acta, Part B, 45(4 5), 1990, 481 491. 

Z. Zhang and X. Ma, Methods for correction of spectral interferences in inductively coupled plasma atomic emission spectrometry, Ciirr. Top. Anal. Chem., 3, 2002, 105-123. 

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. 

I. Rodushkin, T. Ruth, D. Klockare, Non-spectral interferences caused by a saline water matrix in Q and high resolution inductively coupled plasma mass spectrometry, J. Anal. Atom. Spectrom., 13 (1998), 159-166. 

In addition, quantitative and qualitative elemental analysis of inorganic compounds with high accuracy and high sensitivity can be effected by mass spectrometry. For elemental analysis, atomization of the analysed sample that corresponds to the transformation of solid matter in atomic vapour and ionization of these atoms occur in the source. These atoms are then sorted and counted with the help of mass spectrometry. The complete decomposition of the sample in the ionization source into its constituent atoms is necessary because incomplete decomposition results in complex mass spectra in which isobaric overlap might cause unsuspected spectral interferences. Furthermore, the distribution of any element in different species leads to a decrease in sensitivity for this element. 

The disadvantages of electrothermal atomisation (ETA) — atomic absorption spectrometry (AAS) are the physical, chemical and spectral interferences, these being more severe than with flame atomic absorption spectrometry (FAAS), and which depend critically upon the experimental and operational conditions within the atomiser and the nature of the chemical pretreatment used. It is not intended to discuss here the theoretical aspects of these interferences which have been reviewed excellently elsewhere [2], but it is pertinent to consider briefly how these interferences affect the various stages of the analysis and how they may be minimised. 

Machat, J., Otruba, V., Kanicky, V. Spectral and non-spectral interferences in the determination of selenium by inductively coupled plasma atomic emission spectrometry. J. Anal. At. Spectrom. 17, 1096-1102 (2002)... 

When a small-bore column, such as 0.5 mm i.d., was used, aU peaks appeared simultaneously if the volume of the retained stationary phase was over 15%. However, if the retention volume of the stationary phase was less than 10% in a small-bore column, peak separation was observed as shown in Fig. 5. " Each peak was detected by plasma atomic emission spectrometry. This peak profile shows enrichment profiles with separation of Mg, Cu, Mn, and Ca in tap water. The intensity of Ca is shown in the right axis, 3 orders higher than that of the other elements, while the intensity of Mn is amplified 10 times. The spectral interference of Ca to the signal of Cu is observed. This separation phenomenon is considered to be quite useful for exact determination of trace metals. 

The general application of LEI spectrometry to the determination of trace metals has been somewhat limited but progress in this area should continue. Alloy analyses are particularly amenable to LEI spectrometry because of the absence of an ionizable sample matrix. Indium (303.9 nm) has been determined in a nickel-based high temperature alloy31. Atomic absorption spectrometry of this sample requires time-consuming extraction procedures to remove concomitant metals which contribute to spectral interferences. After dissolution of the alloy sample with acids, the concentration of indium was determined to be 35 pg/g by LEI spectrometry. 

The resolution and selectivity in ICP emission comes primarily from the monochromator. As a result, a high-resolution monochromator can isolate the analyte spectral line from lines of concomitants and background emission. It can thus reduce spectral interferences. In atomic absorption spectrometry, the resolution comes primarily from the very narrow hollow cathode lamp emission. The monochromator must only isolate the emission line of the analyte element from lines of impurities and the fill gas, and from background emission from the atomizer. A much lower resolution is needed for this puipose. 

When designing instruments for atomic spectrometry the central aim is to realize fully the figures of merit of the methods. They include the power of detection and its relationship to the precision, the freedom from spectral interferences causing systematic errors and the price/performance ratio, these being the driving forces in the improvement of spectrochemical methods (Fig. 7). 

The oldest of the spectroscopic radiation sources, a flame, has a low temperature (see Section 4.3.1) but therefore good spatial and temporal stability. It easily takes up wet aerosols produced by pneumatic nebulization. Flame atomic emission spectrometry [265] is still a most sensitive technique for the determination of the alkali elements, as eg. is applied for serum analysis. With the aid of hot flames such as the nitrous oxide-acetylene flame, a number of elements can be determined, however, not down to low concentrations [349]. Moreover, interferences arising from the formation of stable compounds are high. Further spectral interferences can also occur. They are due to the emission of intense rotation-vibration band spectra, including the OH (310-330 nm), NH (around 340 nm), N2 bands (around 390 nm), C2 bands (Swan bands around 450 nm, etc.) [20], Also analyte bands may occur. The S2 bands and the CS bands around 390 nm [350] can even be used for the determination of these elements while performing element-specific detection in gas chromatography. However, SiO and other bands may hamper analyses considerably. 

A modification of the GFAAS method for determining selenium levels in human urine was described by Saeed (1986). In this electrothermal atomic absorption spectrometry (EAAS) method, nitric acid, nickel, and platinum are added to the graphite cell. The addition of nickel helps to mask the spectral interference from phosphates in urine. EAAS has been used to determine selenium levels in human spermatozoa (Suistomaa et al. 1987). 

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