Sample atomization techniques, atomic

Although physical studies of the electronic structure of surfaces have to be performed under UHV conditions to guarantee clean uncontaminated samples, the technique does not require vacuum for its operation. Thus, in-situ observation of processes at solid-gas and solid-liquid interfaces is possible as well. This has been utilized, for instance, to directly observe corrosion and electrode processes with atomic resolution [5.2, 5.37]. 

Techniques for analysis of different mercury species in biological samples and abiotic materials include atomic absorption, cold vapor atomic fluorescence spectrometry, gas-liquid chromatography with electron capture detection, and inductively coupled plasma mass spectrometry (Lansens etal. 1991 Schintu etal. 1992 Porcella etal. 1995). Methylmercury concentrations in marine biological tissues are detected at concentrations as low as 10 pg Hg/kg tissue using graphite furnace sample preparation techniques and atomic absorption spectrometry (Schintu et al. 1992). 

A chloric acid digestion was used by Backer 2 391 for the preparation of tissue samples. The digest is simply diluted to determine iron, zinc, and copper. The tantalum sampling boat technique was used by Emmermann and Luecke 2531 to measure lead, zinc, and silver in prepared soil solutions. White 1S81 treated ashed plants with hydroxylamine in IN hydrochloric acid to reduce and dissolve oxides of manganese, prior to its determination by atomic absorption spectroscopy. 

Atomic techniques such as atomic absorption spectrometry (AA), inductively coupled plasma-optical emission spectrometry (ICP-OES), and inductively coupled plasma-mass spectrometry (ICP-MS), have been widely used in the pharmaceutical industry for metal analysis.190-192 A content uniformity analysis of a calcium salt API tablet formulation by ICP-AES exhibited significantly improved efficiency and fast analysis time (1 min per sample) compared to an HPLC method.193... 

Transmission electron microscopy (TEM) is a powerful and mature microstructural characterization technique. The principles and applications of TEM have been described in many books [16 20]. The image formation in TEM is similar to that in optical microscopy, but the resolution of TEM is far superior to that of an optical microscope due to the enormous differences in the wavelengths of the sources used in these two microscopes. Today, most TEMs can be routinely operated at a resolution better than 0.2 nm, which provides the desired microstructural information about ultrathin layers and their interfaces in OLEDs. Electron beams can be focused to nanometer size, so nanochemical analysis of materials can be performed [21]. These unique abilities to provide structural and chemical information down to atomic-nanometer dimensions make it an indispensable technique in OLED development. However, TEM specimens need to be very thin to make them transparent to electrons. This is one of the most formidable obstacles in using TEM in this field. Current versions of OLEDs are composed of hard glass substrates, soft organic materials, and metal layers. Conventional TEM sample preparation techniques are no longer suitable for these samples [22-24], Recently, these difficulties have been overcome by using the advanced dual beam (DB) microscopy technique, which will be discussed later. 

X-ray fluorescence is a type of atomic spectroscopy since the energy transitions occur in atoms. However, it is distinguished from other atomic techniques in that it is nondestructive. Samples are not dissolved. They are analyzed as solids or liquids. If the sample is a solid material in the first place, it only needs to be polished well, or pressed into a pellet with a smooth surface. If it is a liquid or a solution, it is often cast on the surface of a solid substrate. If it is a gas, it is drawn through a filter that captures the solid particulates and the filter is then tested. In any case, the solid or liquid material is positioned in the fluorescence spectrometer in such a way that the x-rays impinge on a sample surface and the emissions are measured. The fluorescence occurs on the surface, and emissions originating from this surface are measured. 

Conventional flame techniques present problems when dealing with either small or solid samples and in order to overcome these problems the electrothermal atomization technique was developed. Electrothermal, or flameless, atomizers are electrically heated devices which produce an atomic vapour (Figure 2.36). One type of cuvette consists of a graphite tube which has a small injection port drilled in the top surface. The tube is held between electrodes, which supply the current for heating and are also water-cooled to return the tube rapidly to an ambient temperature after atomization. 

Flow injection analysis is based on the injection of a liquid sample into a continuously flowing liquid carrier stream, where it is usually made to react to give reaction products that may be detected. FIA offers the possibility in an on-line manifold of sample handling including separation, preconcentration, masking and color reaction, and even microwave dissolution, all of which can be readily automated. The most common advantages of FIA include reduced manpower cost of laboratory operations, increased sample throughput, improved precision of results, reduced sample volumes, and the elimination of many interferences. Fully automated flow injection analysers are based on spectrophotometric detection but are readily adapted as sample preparation units for atomic spectrometric techniques. Flow injection as a sample introduction technique has been discussed previously, whereas here its full potential is briefly surveyed. In addition to a few books on FIA [168,169], several critical reviews of FIA methods for FAAS, GF AAS, and ICP-AES methods have been published [170,171]. 

STM was the first of a class of techniqnes known as scanning probe microscopy. Atomic force microscopy (AFM), invented later in the 1980s, is currently the most widely used of these techniques. Both STM and AFM depend on probes with atomically sharp tips these probes are manenvred over the snrface of the sample to be imaged, maintaining atom-scale distances between the probe and sample. Both techniques are capable of picking np atoms individnally and placing them precisely on surfaces (7). 

This section starts with a discussion of selectivity for the most extended analytical atomic techniques based on optical spectrometry. Then, aspects such as detection limits (DLs), linear ranges, precision, versatility and sample throughput will be presented. The section ends with a brief comparison of the... 

Further, in atomic spectrometry we must face the serious problem that the behaviour (atomisation/excitation characteristics) of the analyte in the calibration samples should be the same as in the future unknown samples where the analyte of interest has to be quantified, otherwise peak displacement and changes of the peak shape may cause serious bias in the predictions. Fortunately, many atomic techniques analyse aqueous extracts or acid solutions of the (pretreated) samples and current working procedures match the amount of acids in the calibration and treated samples, so the matrices become rather similar. Current practices in method development involve studying potential interferents. The analyte is fixed at some average concentration (sometimes studies are made at different concentrations) and the effects of a wide number of potential interferents are tested. They include major cations, anions and... 

Analytical methods for monitoring the compounds were developed or modified to permit the quantification of all 23 compounds of interest. As noted earlier, the compounds were initially studied in small-scale extractions by groups. This approach assured minimal interferences in the analyses conducted during the initial supercritical fluid carbon dioxide extractions. Table II summarizes the data on the recovery of organics from aqueous samples containing the compounds of interest at concentration levels listed in Table I when the sample preparation techniques and analytical methods described were used. For each experimental run, blank and spiked aqueous samples were carried through the sample prepration and analytical finish steps to ensure accurate and reproducible results. Analyses of sodium, calcium, and lead content were also conducted on selected samples by using standard atomic ab-... 

Conventional AA instruments (Figure 1) use a flame atomization system for liquid sample vaporization. An air-acetylene flame (2300°C) is used for most elements. A higher temperature nitrous oxide-acetylene flame (2900°C) is used for more refractory oxide forming elements. Electrothermal atomization techniques such as a graphite furnace can be used for the direct analysis of solid samples. 

GC-MIP systems have been investigated in considerable detail. Because of the low power of the plasma, it is easily quenched if the normal, atomic spectrometric sample introduction techniques, such as nebulisation, are used. Capillary columns overcome this problem as they require only low flow rates and small sample sizes more compatible with stable plasma operation. The capillary columns can be passed out of the oven, down a heated line, and the end of the column placed in the plasma torch just before the plasma, thus preventing any sample loss. A makeup gas is usually introduced via a side arm in the torch to sustain the plasma (Fig. 4.1, Greenway and Barnett, 1989). Other dopant gases can also be added in this way to prolong the lifetime of the torch and improve the plasma characteristics. 

Laborda, F., E. Bolea, and J.R. Castillo. 2007. Electrochemical hydride generation as a sample introduction technique in atomic spectrometry Fundamentals, interferences and applications. Anal. Bioanal. Chem. 388 743-775. 

Nielson, J. M., and H. A. Kornberg Multidimensional Gamma-Ray Spectrometry and its Use in Biology. Radioisotope Sample Measurement Techniques in Medicine and Biology, pp. 3—15. Vienna International Atomic Energy Agency 1965. 

With the main resonance line for cadmium at 228.8 nm, it is hardly surprising that this element is not determined usefully by flame AES. However cadmium is a very easily atomized element, and the determination by flame AAS is sensitive, with detection limits sometimes as low as 1 ng ml-1 often being cited for the air-acetylene flame.1 Determination by flame AFS may result in detection limits two orders of magnitude lower than this, if a suitable excitation source is available.12 The determinations in acetylene flames are virtually free from chemical interference. Because of the ease of atomization, the element may be readily determined using atom-trapping techniques or boat or cup techniques, as discussed in Chapter 6. Recently a cold vapour sample introduction technique has also been suggested for cadmium determination.13,14... 

Atomic absorption has become the primary method for determining metal concentrations in industrial hygiene samples. The types of samples that can be analyzed in AAS will be discussed along with acid digestion methods and AAS atomization techniques. No attempt will be made to thoroughly review the theory... 

These atomization techniques are used in NIOSH, AIHA, and APHA approved (recommended) methods (5-7). Although the purpose of this discussion is MS techniques, one must briefly consider collection of samples. The primary method of collecting metal dust samples and fume samples are 0.8 urn and 0.45 urn mixed cellulose ester filters. The filter is dissolved in acid or leached with dilute base, acid, or distilled water to give an analyte for MS analysis. A general procedure P CAM 173 (5), was developed by NIOSH for the analysis of metals. This method provides a starting point and standard of comparison for the analysis of metals. 

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

The technique may be subject to a number of positive and/or negative systematic errors, depending on the element to be determined, the instrumental technique used, the matrix composition, and still other factors. However, as shown in Table 2.2, there is a tendency towards the use of the standard additions method and CRMs to minimize some possible matrix effects and to ensure validity of results. Nevertheless, it appears from the survey of the literature that the solubilization sampling introduction technique compares favorably with other atomic spectrometric methods for the determination of trace elements in a variety of matrices. 

The method of sample preparation to be used for a given analysis is governed by the nature and concentration of the analyte, the nature (solid or liquid) and type of matrix, the available sample amount, and also by the instrumental technique employed. Freeze-dried samples will require some form of digestion or dissolution in order to be analyzed by a classic atomic technique (i.e., using nebuliza-tion). Liquids might be analyzed by direct nebulization, but this is not always possible due to matrix interferences. Milk pretreatment may be necessary under such circumstances. 

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