Spectrometric techniques atomic absorption spectrometry

It is an advantage of electroanalysis and its apparatus that the financial investment is low in comparison, for instance, with the more instrumental spectrometric methods real disadvantages are the need to have the analyte in solution and to be familiar with the various techniques and their electrochemistry it is to be regretted that the knowledge of chemistry and the skill needed often deter workers from applying electroanalysis when this offers possibilies competitive with more instrumental methods (cf., stripping voltammetry versus atomic absorption spectrometry). 

A convenient method is the spectrometric determination of Li in aqueous solution by atomic absorption spectrometry (AAS), using an acetylene flame—the most common technique for this analyte. The instrument has an emission lamp containing Li, and one of the spectral lines of the emission spectrum is chosen, according to the concentration of the sample, as shown in Table 2. The solution is fed by a nebuhzer into the flame and the absorption caused by the Li atoms in the sample is recorded and converted to a concentration aided by a calibration standard. Possible interference can be expected from alkali metal atoms, for example, airborne trace impurities, that ionize in the flame. These effects are canceled by adding 2000 mg of K per hter of sample matrix. The method covers a wide range of concentrations, from trace analysis at about 20 xg L to brines at about 32 g L as summarized in Table 2. Organic samples have to be mineralized and the inorganic residue dissolved in water. The AAS method for determination of Li in biomedical applications has been reviewed . 

The most frequently applied analytical methods used for characterizing bulk and layered systems (wafers and layers for microelectronics see the example in the schematic on the right-hand side) are summarized in Figure 9.4. Besides mass spectrometric techniques there are a multitude of alternative powerful analytical techniques for characterizing such multi-layered systems. The analytical methods used for determining trace and ultratrace elements in, for example, high purity materials for microelectronic applications include AAS (atomic absorption spectrometry), XRF (X-ray fluorescence analysis), ICP-OES (optical emission spectroscopy with inductively coupled plasma), NAA (neutron activation analysis) and others. For the characterization of layered systems or for the determination of surface contamination, XPS (X-ray photon electron spectroscopy), SEM-EDX (secondary electron microscopy combined with energy disperse X-ray analysis) and... 

The contribution of flow analysis to improving the performance of atomic spectrometry is especially interesting in the field of standardisation. FIA can provide a faster and reliable method to relate the absorbance, emission or counts (at a specific mass number) to the concentration of the elements to be determined. In fact, flow analysis presents specific advantages to solving problems related to the sometimes short dynamic concentration ranges in atomic absorption spectrometry, by means of on-line dilution. The coupling of FI techniques to atomic spectrometric detectors also offers tremendous possibilities to carry out standard additions or internal standardisation. 

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. 

Investigations of lead speciation in various environmental samples have relied upon gas and liquid chromatographic separations coupled to mass spectrometric and atomic absorption spectrometric detectors. The combination of atomic absorption spectrometry with gas chromatography (GC-AAS) has proved to be the most widely applied technique. Sample types have included air, surface water, air particulates, sediments, grass, and clinical materials such as blood. A review of speciation analyses of organolead compounds by GC-AAS, with emphasis on environmental materials, was published (Lobinski et al., 1994). 

Spectrometric techniques based on atomic absorption or the emission of radiation flame atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (ETAAS), inductively coupled plasma-optical emission spectrometry (ICP-OES), inductively coupled plasma-mass spectrometry (ICP-MS), and cold vapor (CV)/hydride generation (HG), mainly for trace and ultratrace metal determinations. 

Flame Spectrometry in Environmental Chemical Analysis A Practical Guide is a simple, user-friendly guide to safe flame spectrometric methods for environmental samples. It explains key processes involved in achieving accurate and reliable results in atomic absorption spectrometry, atomic fluorescence spectrometry and flame emission spectrometry, showing the inter-relationship of the three techniques, and their relative importance. 

Since some form of liquid sample presentation is common to most atomic spectrometric techniques, these may be considered as the method of choice for the identification and quantification of trace metals in liquid foods. In spectrometric techniques, after conversion of the sample into microspray, chemical flames as in flame atomic absorption spectrometry (FAAS) and atomic... 

Background Caused by Filters. Since all of the particles were collected on membrane filters it was necessary to determine the blank metal concentrations in the filter. This enabled an estimation of how many particles must be collected in order that the levels of the metals were significantly greater than the blank filter. For this study, both neutron and flame atomic absorption spectrometric analyses were used and the results are shown in Table I. The analyses by neutron activation were made on the filter directly whereas those by atomic absorption spectrometry were obtained by extracting the filter with nitric acid (16M Ultrex). There are apparent differences between the two sizes of membrane filters which are probably related to the fact that these filter sets were obtained at different times. Also, while the metal blanks within a particular batch of filters vary by negligible amoimts, the variations between batches are considerable. These determinations are near the detection limits for both techniques, and therefore there are considerable uncertainties associated with the results. However, these blanks did indicate the minimum level of metals which must be collected if the analyses are to be significant. 

In terms of this group of atomic spectrometric techniques, optical emission spectrometry (OES) is the oldest and most established. Atomic absorption spectrometry (A AS) and atomic fluorescence spectrometry (AES) are two other important types of atomic spectrometry techniques. In this section, AAS and AES will be discnssed only briefly elemental analysis based on ICP spectrometry will be discnssed in more detail, specifically ICP-OES... 

Various atomic spectrometric methods form an essential part of the modern instrumental methods of analysis. The most widely used of these methods is atomic absorption spectrometry (AAS). The popularity of AAS can be attributed to its selectivity, simplicity, and convenience in use. The high sensitivity of graphite furnace AAS is very important in many applications. Plasma atomic emission spectrometry (plasma AES) has become more and more important for the determination of traces in a great variety of samples. The complementary nature of plasma AES and AAS capabilities for trace elemental analysis is an important feature of these techniques. Inductively coupled plasma mass spectrometry (ICP-MS) has become a hot analytical technique during the last few years, and is being used in many branches of science. 

AFS is a method of elemental analysis that involves the use of a light source to excite gaseous atoms radiatively to a higher energy level, followed by a deactivation process that involves emission of a photon. This emission process provides the measured fluorescence signal. AFS can be distinguished from the related atomic spectrometric techniques of atomic absorption spectrometry (AAS) and atomic emission spectrometry (AES) because it involves both radiative excitation and deexcitation. 

Liposoluble samples such as creams or oils can be directly emulsified in water, with the aid of a surfactant, and some metallic elements can be determined by atomic spectrometric techniques without any pretreatment and using aqueous standards. For example, sunscreen creams have been emulsified and zinc (present as zinc oxide) determined by atomic absorption spectrometry. 

Atomic spectrometric techniques such as flame atomic absorption spectrometry (FAAS), electrothermal AAS (ETAAS), inductively coupled plasma atomic emission spectrometry (ICP-AES), and ICP-MS are used for the determination of elements, particularly metals. ICP-MS is the most sensitive, typically with microgram per liter detection limits and multielement capability but it has high start-up and operating costs. UV-visible spectrophotometry is also used for the determination of metal ions and anions such as nitrate and phosphate (usually by selective deriva-tization). It is a low cost and straightforward technique, and portable (handheld) instruments are available for field deployment. Flow injection (FI) provides a highly reproducible means of manipulating solution chemistry in a contamination free environment, and is often used for sample manipulation, e.g., derivatization, dilution, preconcentration and matrix removal, in conjunction with spectrometric detection. Electroanalytical techniques, particularly voltammetry and ion-selective electrodes (ISEs), are... 

In recent years, the coupling of ion chromatography with element-specific detection methods has increasingly gained importance. Element-specific detection is carried out with atomic spectrometric techniques including atomic absorption spectrometry (AAS), atomic emission spectrometry (ICP-OES), and the coupling between ICP and mass spectrometry (ICP-MS). 

Traditionally, gold analysis in electroplating baths was carried out with conventional methods such as precipitation or titration techniques. However, these methods require time-consuming sample preparation to break the complex bond. Today, spectrometric methods such as atomic absorption spectrometry (AAS) or ICP-OES are usually applied, but they are also somewhat problematic... 

Trace elements in leachates and digests of loaded filters, sediment traps and centrifuge materials can be detected using different atomic absorption spectrometric techniques. Depending on the amount of available sample solution and concentration of the respective elements either common flame, flame-injection or electrothermal AAS (ETAAS) are selected. The principle of atomic absorption spectrometry, its advantages and limitations have... 

Atomic absorption spectrometry is a usefiil technique for the determination of traces of heavy metals in polymers. Generally, the polymer is ashed at a maximum temperature of 450 C to avoid losses of elements by volatilization, then the ash is digested with warm nitric acid prior to spectrometric analysis, (Method 71). 

For determination of the elements, mainly spectrometric techniques are used here. Depending on the kind of element and the expected concentration level, the following methods are applied flame atomic emission spectrometry (flame AES), flame atomic absorption spectrometry (flame AAS), inductively coupled plasma optical emission spectrometry (ICP-OES), electrothermal atomisation (graphite furnace) atomic absorption spectrometry (ETA-AAS), inductively coupled plasma mass spectrometry (ICP-MS), spectrophotometry and segmented flow analysis (SFA). Besides, potentiometry (ion selective electrodes (ISE)) and coulometry will be encountered. In many cases, more than one method is described to determine a component. This provides a reference, as well as an alternative in case of instrumental or analytical problems. 

The most commonly used are the atomic spectrometric techniques, especially FAAS, electrothermal atomic absorption spectrometry (ETAAS) and inductive coupled plasma with atomic anision spectrometry (ICP-AES). ICP-MS, X-ray fluorescence spectrometry (XRFS), electroanalytical techniques, UVA IS spectrometry and FL have also been used among others. 

Atomic Spectrometric Techniques Optical Detection Atomic Emission Spectrometry Atomic Absorption Spectrometry Atomic Fluorescence Spectrometry Detection of Elemental Ions Comparisons of the Atomic Spectrometric Techniques... 

The basic instrumentation used for spectrometric measurements has already been described in the previous chapter (p. 277). Methods of excitation, monochromators and detectors used in atomic emission and absorption techniques are included in Table 8.1. Sources of radiation physically separated from the sample are required for atomic absorption, atomic fluorescence and X-ray fluorescence spectrometry (cf. molecular absorption spectrometry), whereas in flame photometry, arc/spark and plasma emission techniques, the sample is excited directly by thermal means. Diffraction gratings or prism monochromators are used for dispersion in all the techniques including X-ray fluorescence where a single crystal of appropriate lattice dimensions acts as a grating. Atomic fluorescence spectra are sufficiently simple to allow the use of an interference filter in many instances. Photomultiplier detectors are used in every technique except X-ray fluorescence where proportional counting or scintillation devices are employed. Photographic recording of a complete spectrum facilitates qualitative analysis by optical emission spectrometry, but is now rarely used. 

The basic instrumentation used for spectrometric measurements has already been described in Chapter 7 (p. 277). The natures of sources, monochromators, detectors, and sample cells required for molecular absorption techniques are summarized in Table 9.1. The principal difference between instrumentation for atomic emission and molecular absorption spectrometry is in the need for a separate source of radiation for the latter. In the infrared, visible and ultraviolet regions, white sources are used, i.e. the energy or frequency range of the source covers most or all of the relevant portion of the spectrum. In contrast, nuclear magnetic resonance spectrometers employ a narrow waveband radio-frequency transmitter, a tuned detector and no monochromator. 

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