Matrices atomic spectrometry

Different analytical procedures have been developed for direct atomic spectrometry of solids applicable to inorganic and organic materials in the form of powders, granulate, fibres, foils or sheets. For sample introduction without prior dissolution, a sample can also be suspended in a suitable solvent. Slurry techniques have not been used in relation to polymer/additive analysis. The required amount of sample taken for analysis typically ranges from 0.1 to 10 mg for analyte concentrations in the ppm and ppb range. In direct solid sampling method development, the mass of sample to be used is determined by the sensitivity of the available analytical lines. Physical methods are direct and relative instrumental methods, subjected to matrix-dependent physical and nonspectral interferences. Standard reference samples may be used to compensate for systematic errors. The minimum difficulties cause INAA, SNMS, XRF (for thin samples), TXRF and PIXE. 

Flow-injection (FI) on-line analyte preconcentration and matrix removal techniques greatly enhance the performance of atomic spectrometry [348], By using USN with membrane desolvation (MDS) as the interface, FI sorbent extraction can be directly coupled with ICP-MS for the analysis of organic solutions [349]. 

Flow injection manifold for coupling with atomic spectrometry. The column can be used for preconcentration, matrix removal or chromatography. 

The application of atomic spectroscopic instruments as element-specific detectors in chromatography has been reviewed by van Loon More recently, Krull has extensively reviewed their use in high pressure liquid chromatography (HPLC). Atomic spectrometry has found wide acceptance in the field of liquid chromatography because, in most cases, the fractions can be directly analysed after elution from the column. However, it is possible to use the technique for the analysis of solid samples without first dissolving the matrix. This is particularly useful after electrophoresis, where the fractions are fixed either in a gel or on paper. Kamel et al. have shown that it is possible to cut the appropriate sections and insert them into the carbon furnace for analysis. The disadvantage of this approach is that the precision is usually poorer (about 10%) and it is difficult to calibrate the instrument. Nevertheless, this approach is very useful if it is used for qualitative speciation. 

A large part of the success of the combination of FI and atomic spectrometry is due to its ability to overcome interference effects. The implementation of some pretreatment chemistry in the FI format makes it possible to separate the species of the analyte from the unwanted matrix species e.g. by converting each sample into a mixture of analyte(s) and a standard background matrix, designed not to interfere in the atom formation process and/or subsequent interaction with radiation in the atom cell). Often such separation procedures result also in an increased analyte mass flux into the atom source with subsequent improvements in sensitivity and detection limits. 

Table 2.9 presents the L9(3 ) orthogonal matrix, used several times in atomic spectrometry (e.g. [4,5]). 

Every coupling application favors one part of the coupling system. A dominating chromatography part leads to the speciation analysis [5,6,26,27]. The elemental specific detection facilities of atomic spectrometry are strongly favored over the multielement capabilities. An inversion of this construction leads to multielement trace analysis in complex matrices with the use of chromatographic equipment as powerful preconcentration and matrix elimination tool [13k The ability of chromatography for a further time resolution between the separated traces is not really required because of the excellent elemental specific detection capabilities of atomic spectrometry. 

Most important features of atomic spectrometry are the element specific detection and the superior sensitivity. Features such as the large dynamic range, the relative freedom from matrix effects even when atomic spectrometry is coupled to chromatography can be used more extensively to save time and to earn more accurate data using coupling techniques. 

The most suitable techniques for the rapid, accurate determination of the elemental content of foods are based on analytical atomic spectrometry, for example, atomic absorption spectrometry (AAS), atomic emission spectrometry (AES), and mass spectrometry, the most popular modes of which are Game (F), electrothermal atomization (ET), and hydride generation (HG) AAS, inductively coupled plasma (ICP), microwave-induced plasma (MIP), direct current plasma (DCP) AES, and ICP-MS. Challenges in the determination of elements in food include a wide range of concentrations, ranging from ng/g to percent levels, in an almost endless combination of analytes with matrix speci be matrices. 

Prior to quantitation of analyte by atomic spectrometry it is usually necessary to destroy the organic matrix and bring the element into solution. Most of the multitude of decomposition procedures reported fall into one of two classes, wet digestion and dry ashing. Often many variants of each procedure provide adequate results with a variety of analytes and matrices. Several commonly used procedures of general applicability are described below specific details are found in the sections dealing with the determination of individual elements. The reader is referred to several good sources of information on sample decomposition for fuller details and discussion [8h, 34,138—140]. The procedures described below result in essentially... 

When using matrix modification the aim is to make efficient use of the thermochemical properties of the elements so as to be able to remove the matrix more effectively or to immobilize the analytes. Both should bring the goal of a matrix-free determination nearer, along with its advantages with respect to ease of calibration and minimization of systematic errors. Matrix modification has developed into a specific line of research in atomic spectrometry. 

As the sample volatilization is due to cathodic sputtering only, matrix interferences as a result of the thermochemical properties of the elements do not occur. This has been shown impressively in early comparative studies of glow discharge atomic spectrometry and spark emission spectrometry with aluminum samples (Fig. 107) [480]. It must be stated, however, that with advanced sparks, where through the use of fiber optics only those parts of the spark plasma are observed that are not involved in sample ablation, matrix interferences in the case of spark emission spectrometry are also lower. The analysis of similar alloys with different metallographic structures by glow discharge atomic spectrometry can often be carried out with one calibration. 

The best-known technique based on a combination of methods is ICP-MS. Here, the excited atoms are introduced upon their return to a lower energy level, through an interface into the ion source of a quadru-pole of a mass spectrometer. The ICP thus acts as an ion source and the mass spectrometer as the ion detector. The latest development in atomic spectrometry is the electrothermal evaporation-ICP-MS technique, where a graphite furnace is coupled to an ICP-MS. In this case, use is made of the most remarkable property of a graphite furnace (elimination of matrix interferences) by a graphite tube atomizer and subsequent transport of the atomic phase into the plasma and quadrupole. 

Ingle CP, Sharp BL, Horstwood MSA, Parrish RR, and Lewis DJ (2003) Instrument response functions, mass bias and matrix effects in isotope ratio measurements and semi-quantitative analysis by single and multicollector ICP-MS. Journal of Analytical Atomic Spectrometry 18 219-229. 

Atomic spectrometry generally requires prior dissolution of the sample, which can be carried out with either acids or organics solvents, but in some cases necessitates destroying the matrix by means of a wet acid treatment or a dry digestion. This can be a serious drawback, but the new strategies for sample preparation, based on the use of microwave-assisted digestion procedures for sample dissolution and... 

Atomic spectrometry Laser-induced atomic emission spectroscopy (AES) is a fast technique to determine directly elemental sulfur. Practically no matrix effects occur and the method is virtually nondestructive and easy to use. A disadvantage is the rather poor sensitivity, for example, a typical detection limit for sulfur in steel is 70pgperg. With indirect atomic absorption spectrometry clearly better... 

Sahayam, A.C., Jiang, S, Wan, C. (2004) Determination of ultra-trace impurities in high purity gallium arsenide by inductively coupled plasma mass spectrometry after volatilization of matrix. Journal of Analytical Atomic Spectrometry, 19,407-409. 

In the case of atomic spectrometry [e.g.. atomic absorption (AA), inductively coupled plasma-optical emission spectrometry (ICP-OES), inductively coupled plasma-mass spectrometry (ICP-MS)] matrix interference due to incomplete digestion may manifest itself as differences in the suction rates and aerosol yields for samples relative to calibrating solutions. Such differences may also reflect differences in the bonding states of the elements, which in turn leads to systematic errors and problems with calibration. 

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