Inductively coupled plasma-atomic emission interferences

Flame AAS (often abbreviated FAAS) was until recently the most widely used method for trace metal analysis. However, it has now largely been superseded by inductively coupled plasma atomic emission spectrometry (see Chapter 4). It is particularly applicable where the sample is in solution or readily solubilized. It is very simple to use and, as we shall see, remarkably free from interferences. Its growth in popularity has been so rapid that on two occasions, the mid-1960s and the early 1970s, the growth in sales of atomic absorption instruments has exceeded that necessary to ensure that the whole face of the globe would be covered by atomic absorption instruments before the end of the century. 

Line Coincidence Tables for Inductively Coupled Plasma Atomic Emission Spectrometry, Boumans, P.W.J.M, Pergamon Press, New York, 1984. The most comprehensive compilation available of sensitive lines for use in ICPAES, with listings of potential interferences. 

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. 

The inductively coupled plasma13 shown at the beginning of the chapter is twice as hot as a combustion flame (Figure 21-11). The high temperature, stability, and relatively inert Ar environment in the plasma eliminate much of the interference encountered with flames. Simultaneous multielement analysis, described in Section 21 1. is routine for inductively coupled plasma atomic emission spectroscopy, which has replaced flame atomic absorption. The plasma instrument costs more to purchase and operate than a flame instrument. 

Inductively coupled plasma atomic emission spectrometry has proved to be an excellent technique for the direct analysis of soil extracts because it is precise, accurate and not time-consuming, the level of matrix interference being very low. Of course, the graphite furnace technique yields better detection limits than the inductively coupled plasma procedure. 

Procedure Use an Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES), or equivalent instrumentation with similar capabilities. Follow the instrument manufacturer s instructions for setting instrument parameters for assay of cadmium. Select appropriate background correction points for the cadmium analyte according to the recommendations of the instrument manufacturer. Select analytical wavelengths to yield adequate sensitivity and freedom from interference. 

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)... 

Knowledge of the atomic spectra is also very important so as to be able to select interference-free analysis lines for a given element in a well-defined matrix at a certain concentration level. To do this, wavelength atlases or spectral cards for the different sources can be used, as they have been published for arcs and sparks, glow discharges and inductively coupled plasma atomic emission spectrometry (see earlier). In the case of ICP-OES, for example, an atlas with spectral scans around a large number of prominent analytical lines [329] is available, as well as tables with normalized intensities and critical concentrations for atomic emission spectrometers with different spectral bandwidths for a large number of these measured ICP line intensities, and also for intensities calculated from arc and spark tables [334]. The problem of the selection of interference-free lines in any case is much more complex than in AAS or AFS work. 

Sulfate S is extracted from air-dry soil of <2 mm particle size with deionised water, using a soil to solution ratio of 1 5 and an extraction time of 17 hour at 25°C. This extracting solution will not displace adsorbed S, and will not necessarily dissolve all the gypsum that could be present. The extracted S is then determined in an aliquot of clear soil extract by inductively coupled plasma atomic emission spectrometry (ICPAES). In conjunction with vacuum optics, ICPAES is an efficient technique for the measurement of S in soil extracts. At the wavelength, 182.036 nm, there is virtually no interference from Ca2+. 

Once in solution, the preferred method for measurement of boron is inductively coupled plasma atomic emission spectroscopy (ICP-AES) or inductively coupled plasma mass spectrometry (ICP-MS). The most widely used nonspectrophotometric method for analysis of boron is probably ICP-MS because it uses a small volume of sample, is fast, and can detect boron concentrations down to 0.15 pgL . When expensive ICP equipment is not available, colorimetric or spectrophotometric methods can be used. However, these methods are often subject to interference (e.g., nitrate, chloride, fluoride), and thus must be used with caution. Azomethine-H has been used to determine boron in environmental samples (Lopez et al. 1993), especially water samples. Another simple, sensitive spectrophotometric method uses Alizarin Red S (Garcia-Campana et al. 1992). 

Inductively coupled plasma-atomic emission spectrometry, an atlas of spectral information. The latter is a most useful handbook by pioneers in plasma spectrochemistry, on specifically ICP-AES, beginning with a background to the information and containing interesting wavelength scans and extensive tabulations of lines and spectral coincidence profiles (spectral interferences). 

Botto, R. I, Matrix Interferences in the Analysis of Organic Solutions by Inductively Coupled Plasma-Atomic Emission Spectrometry, Spectrochimica Acta, Vol. 42B, 1987, pp. 181-189. 

Inductively coupled plasma atomic emission spectrometry (ICP-AES) involves a plasma, usually argon, at temperatures between 6000 and 8000 K as excitation source. The analyte enters the plasma as an aerosol. The droplets are dried, desol-vated, and the matrix is decomposed in the plasma. In the high-temperature region of the plasma, molecular, atomic, and ionic species in various energy states are formed. The emission lines can then be exploited for analytical purposes. Typical detection limits achievable for arsenic with this technique are 30 J,g As/L (23). Due to the rather high detection limit, ICP-AES is not frequently used for the determination of arsenic in biological samples. The use of special nebulizers, such as ultrasonic nebulization, increases the sample transport efficiency from 1-2% (conventional pneumatic nebulizer) to 10-20% and, therefore, improves the detection limits for most elements 10-fold. In addition to the fact that the ultrasonic nebulizer is rather expensive, it was reported to be matrix sensitive (24). Inductively coupled plasma atomic emission spectrometry is known to suffer from interferences due to the rather complex emission spectrum consisting of atomic as... 

Flame atomic absorption was until recently the most widely used techniques for trace metal analysis, reflecting its ease of use and relative freedom from interferences. Although now superceded in many laboratories by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry, flame atomic absorption spectrometry still is a very valid option for many applications. The sample, usually in solution, is sprayed into the flame following the generation of an aerosol by means of a nebulizer. The theory of atomic absorption spectrometry (AAS) and details of the basic instrumentation required are described in a previous article. This article briefly reviews the nature of the flames employed in AAS, the specific requirements of the instrumentation for use with flame AAS, and the atomization processes that take place within the flame. An overview is given of possible interferences and various modifications that may provide some practical advantage over conventional flame cells. Finally, a number of application notes for common matrices are given. 

Depending on the detection technique employed and the purpose of the analysis, it is occasionally sufficient to conduct a relatively simple group separation to isolate the rare earths from the matrix. Neutron activation analysis (NAA), inductively coupled plasma/atomic emission spectroscopy (ICP/AES), and mass spectrometry (ICP/MS) are examples of techniques that have been applied for simultaneous detection/quantitation of individual lanthanides in a mixture of lanthanides. Chemical separation techniques are often required prior to application of these methods because of the susceptibility of element-specific techniques to interferences that may compromise the analysis. 

Determination by hydride generation inductively coupled plasma atomic emission spectrometry after reduction of antimony (V) to antimony (III) by thiourea Spec A = 640 nm trophotometric determination of trace arsenic (V) in water Spec A = 600 nm to avoid antimony interference... 

Daskalova N, Velichkov S, Krasnobaeva N and Slavova P (1992) Spectral interferences in the determination of traces of scandium, yttrium and rare earth elements in pure rare earth matrices by inductively coupled plasma atomic emission spectrometry. Spectrochimica Acta B47 E1595-E1620. 

Maestre S., Mora J. and Todou J. L. (2002) Studies about the origin of the non-spectroscopic interferences caused by sodium and calcium in inductively coupled plasma atomic emission spectrometry. Influence of the spray chamber design, Spectrochim. Acta,... 

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