Analytical atomic spectrometric

Introduction Basis of Analytical Atomic Spectrometric Techniques... 

Generally physical, chemical, and ionization interferences are similar in terms of incidence and extent in all three flame analytical atomic spectrometric techniques, but they are not a severe problem provided the analyst is aware of their existence, and takes the necessary precautions. Spectral interferences are not regarded as a serious problem in flame AAS or flame AFS, but are potentially much more serious in FES. Unless the analyst is certain that a particular FES determination is spectral interference-free for the samples in question, scanning and careful scrutiny of emission spectra from samples and standards is advisable, together with reliability checks using certified reference materials and/or determination at more than one wavelength. 

TABLE 2.1. Analytical Characteristics of Solubilized Forms in Element Determination by Analytical Atomic Spectrometric Techniques... 

Elements Determined / Species Sample/Matrix Analytical Atomic Spectrometric Technique... 

The present book is designed to describe the basic theory of atomic spectroscopy, instrumentation, techniques, and the application of various analytical atomic spectrometric methods (AAS, plasma AES, AFS, and ICP-MS). 

The preparation of aqueous solutions from solids is usually performed after the sample has been ground to a powder of uniform size. Sometimes, samples can be only sparingly soluble in water and therefore organic solvents may be used to dissolve the sample. Organic solvents can increase the sensitivities of atomic spectrometric analyses as a result of increases in the efficiencies of the nebulization of the analyte solutions. When organic solvents are used to dissolve samples non-selective ligands should be added to complex ionic species that would otherwise be insoluble in the organic solvent. 

The major goals for the future development of analytical atomic spectrometry measurements are improved detection Hmits and the development of simple ways of couphng to other analytical techniques. The nebuHzer systems of the spectrometric instruments are the parts that need to be improved in order to achieve these goals. Typically, nebuHzer efficiencies are of the order of 1—2%, and, as a result, they are Hmiting factors for instruments which can cost between 100,000 and 150,000. 

Several different types of chromatography have been coupled with atomic spectrometric detectors. Most applications involving chromatography coupled with atomic spectrometry yield speciation data, i.e. they separate different chemical forms of an analyte. 

Different analytical techniques such as ICP-OES (optical emission spectrometry with inductively coupled plasma source), XRF (X-ray fluorescence analysis), AAS (atomic absorption spectrometry) with graphite furnace and flame GF-AAS and FAAS, NAA (neutron activation analysis) and others, are employed for the trace analysis of environmental samples. The main features of selected atomic spectrometric techniques (ICP-MS, ICP-OES and AAS) are summarized in Table 9.20.1 The detection ranges and LODs of selected analytical techniques for trace analysis on environmental samples are summarized in Figure 9.15.1... 

Routine inorganic elemental analysis is carried out nowadays mainly by atomic spectrometric techniques based on the measurement of the energy of photons. The most frequently used photons for analytical atomic spectrometry extend from the ultraviolet (UV 190-390 nm) to the visible (Vis 390-750 nm) regions. Here the analyte must be in the form of atoms in the gas phase so that the photons interact easily with valence electrons. It is worth noting that techniques based on the measurement of X-rays emitted after excitation of the sample with X-rays i.e. X-ray fluorescence, XRF) or with energetic electrons (electron-probe X-ray micro-analysis, EPXMA) yield elemental information directly from solid samples, but they will not be explained here instead, they will be briefly treated in Section 1.5. 

For a given ICP-OES instrument, the intensity of an analyte line is a complex function of several factors. Some adjustable parameters that affect the ICP source are the radiofrequency power coupled into the plasma (usually about 1 kW), the gas flow rates, the observation height in the lateral-viewing mode and the solution uptake rate of the nebuliser. Many of these factors interact in a complex fashion and their combined effects are different for dissimilar spectral lines. The selection of an appropriate combination of these factors is of critical importance in ICP-OES. This issue will be addressed in Chapter 2, where experimental designs and optimisation procedures will be discussed. Many examples related to ICP and other atomic spectrometric techniques will be presented. 

The choice of the detector becomes crucial when the concentration of analyte species in the sample is very low and low limits of detection are required. For element-specific detection, the major atomic spectrometric techniques, flame AAS, OES, AFS and ICP-MS, are specially suited as chromatographic... 

Atomic spectrometric methods Here, the entire sample is atomized or ionized either by flame or inductively coupled plasma and transferred into the detector. The most common techniques in this class are flame atomic absorption spectrometry (FAAS) and inductively coupled plasma mass spectrometry (ICPMS). A general characteristic of these methods is the determination of the total concentration of the analyte without the direct possibility of distinguishing its specific forms in the sample. 

Metal concentrations are determined using molecular spectrophotometric, atomic spectrometric, and electrochemical techniques. All of these require samples to be homogenous, or at least to contain the smallest possible amounts of organic matter that could interfere with the metal determination by interacting with the metal ions and the analytical reagents. Traditionally, decomposition of the sample in elemental analysis requires it to be mineralized in order to remove the organic content.1 Sample decomposition for total element determination therefore appears to be the recommended procedure on every occasion. 

In this chapter, the description of applications highlights the selection of the instrumentation used as well as the alkaline solubilization sample preparation (often the most critical part of a complete analytical method). The main characteristics of the suspension sample introduction method are also emphasized. A brief discussion on subgroups of these methods, identibed by the atomic spectrometric instrumental approach, is bnally presented. 

The solubilization technique should be used more frequently in combination with atomic spectrometric methods. Further research to improve its analytical performance in terms of LoDs, precision, and accuracy is required. 

A strong preference in speciation analysis is to use a separation step that can be combined with a detection step in an on-line system [45]. In such coupling, analytical selectivity relies on the application of different chromatographic or electrophoretic methods, while the use of atomic spectrometric techniques assures high sensitivity and f>t-for-purpose limits of detection (LoDs). However, hyphenated techniques with element-specif>c detection do not provide structural information on the species. If appropriate standards are available, the assignation of chromatographic peaks can be accomplished by spiking experiments. On the... 

---