Atomic absorption spectrometry sample vaporization

Electrothermal vaporization can be used for 5-100 )iL sample solution volumes or for small amounts of some solids. A graphite furnace similar to those used for graphite-furnace atomic absorption spectrometry can be used to vaporize the sample. Other devices including boats, ribbons, rods, and filaments, also can be used. The chosen device is heated in a series of steps to temperatures as high as 3000 K to produce a dry vapor and an aerosol, which are transported into the center of the plasma. A transient signal is produced due to matrix and element-dependent volatilization, so the detection system must be capable of time resolution better than 0.25 s. Concentration detection limits are typically 1-2 orders of magnitude better than those obtained via nebulization. Mass detection limits are typically in the range of tens of pg to ng, with a precision of 10% to 15%. 

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). 

Nebulization is inefficient and therefore not appropriate for very small liquid samples. Introducing samples into the plasma in liquid form reduces the potential sensitivity because the analyte flux is limited by the amount of solvent that the plasma will tolerate. To circumvent these problems a variety of thermal and electrothermal vaporization devices have been investigated. Two basic approaches are in use. The first involves indirect vaporization of the sample in an electrothermal vaporizer, e.g. a carbon rod or tube furnace or heated metal filament as commonly used in atomic absorption spectrometry [7-9], The second involves inserting the sample into the base of the... 

Atomic absorption spectrometry (AA). This is a standard laboratory analytical tool for metals. The metal is extracted into a solution and then vaporized in a flame. A light beam with a wavelength absorbed by the metal of interest passes through the vaporized sample for example, to measure zinc, a zinc resonance lamp can be used so that the emission and absorbing wavelengths are perfectly matched. The absorption of the light by the sample is measured and Beer s law is applied to quantify the amount present. 

J. Moreda-Pineiro, P. Fopez-Mahia, S. Muniategui-Forenzo, E. Fernandez-Fernandez and D. Prada-Rodriguez, Direct As, Bi, Ge, Hg and Se(IV) cold vapor/hydride generation from coal fly ash slurry samples and determination by electrothermal atomic absorption spectrometry, Spectrochim. Acta, Part B, 57(5), 2002, 883-895. 

S. Rio Segade and J. F. Tyson, Determination of methylmercury and inorganic mercury in water samples by slurry sampling cold vapor atomic absorption spectrometry in a flow injection system after preconcentration on silica C18 modified, Talanta, 71(4), 2007, 1696-1702. 

Carbon Monoxide. Methods for determining carbon monoxide include detection by conversion to mercury vapor, gas filter correlation spectrometry, TDLAS, and grab sampling followed by gas chromatograph (GC) analysis. The quantitative liberation of mercury vapor from mercury oxide by CO has been used to measure CO (73). The mercury vapor concentration is then measured by flameless atomic absorption spectrometry. A detection limit of 0.1 ppbv was reported for a 30-s response time. Accuracy was reported to be 3% at tropospheric mixing ratios. A commercial instrument providing similar performance is available. 

In atomic absorption spectrometry (AA) the sample is vaporized and the element of interest atomized at high temperatures. The element concentration is determined based on the attenuation or absorption by the analyte atoms, of a characteristic wavelength emitted from a light source. The light source is typically a hollow cathode lamp containing the element to be measured. Separate lamps are needed for each element. The detector is usually a photomultiplier tube. A monochromator is used to separate the element line and the light source is modulated to reduce the amount of unwanted radiation reaching the detector. 

The flame must dry, vaporize, and atomize the sample in a reproducible manner with respect to both space and time. Unlike titrimetric and gravimetric analysis, atomic absorption spectrometry is a secondary analytical technique. Concentrations are determined by comparing the absorbance values obtained for samples with those obtained for standards of known determinant concentrations. It is very important, therefore, that samples and standards are always atomized with the same efficiency to produce a cloud of atomic vapour of highly reproducible geometry. If samples and standards behave differently, errors will result. 

M. A. H. Hafez, I. M. M. Kenawy, M. A. Akl, R. R. Lashein, Preconcentration and separation of total mercury in environmental samples using chemically modified chlor-omethylated polystyrene-PAN (ion-exchanger) and its determination by cold vapor atomic absorption spectrometry, Talanta, 53 (2001), 749-760. 

S. R. Segade, J. F. Tyson, Evaluation of two flow injection systems for mercury speciation analysis in fish tissue samples by slurry sampling cold vapor atomic absorption spectrometry, J. Anal. Atom. Spectrom., 18 (2003), 268-273. 

A combination of IPC and inductively coupled plasma (ICP) MS was extensively explored for the speciation of phosphorus, arsenic, selenium, cadmium, mercury, and chromium compounds [108-118] because it provides specific and sensitive element detection. Selenium IPC speciation was joined to atomic fluorescent spectrometry via an interface in which all selenium species were reduced by thiourea before conventional hydride generation [119], Coupling IPC separation of monomethyl and mercuric Hg in biotic samples by formation of their thiourea complexes with cold vapor generation and atomic fluorescence detection was successfully validated [120]. The coupling of IPC with atomic absorption spectrometry was also used for online speciation of Cr(III) and Cr(VI) [121] and arsenic compounds employing hydride generation [122]. 

IPC separation of monomethyl and mercuric Hg in biotic samples by formation of their thiourea complexes, coupled to cold vapor generation and atomic fluorescence detection, was successfully validated [18]. The coupling of IPC with atomic absorption spectrometry was also used for online speciation of arsenic compounds employing hydride generation [17]. In the analytical speciation of chromium using in... 

Mercury, the only metallic element with significant volatility at room temperature, has been conventionally determined for many years by atomic absorption spectrometry, as the mercury vapor detector (W20) is based on this principle. Lindstrom (L7) used a flame to volatilize the mercury in the liquid sample, but determined its concentration in the exhaust gases with the mercury vapor meter after cooling and purification in a filter that removed particulate matter. The method is said to be capable of detecting 0.1 pg % of mercury in the original liquid sample... 

Total Hg in biological matrices was determined using the Cold Vapor Atomic Absorption Spectrometry (CV-AAS) methodology (37). Samples were predigested in a 4 1 HNO3-H2SO4 mixture at 60°C. The digestion was completed with 6%... 

Many researchers have attempted to determine mercury levels in the blood, urine, tissues, and hair of humans and animals. Most methods have used atomic absorption spectrometry (AAS), atomic fluorescence spectrometry (AFS), or neutron activation analysis (NAA). In addition, methods based on mass spectrometry (MS), spectrophotometry, and anodic stripping voltametry (ASV) have also been tested. Of the available methods, cold vapor (CV) AAS is the most widely used. In most methods, mercury in the sample is reduced to the elemental state. Some methods require predigestion of the sample prior to reduction. At all phases of sample preparation and analysis, the possibility of contamination from mercury found naturally in the environment must be considered. Rigorous standards to prevent mercury contamination must be followed. Table 6-1 presents details of selected methods used to determine mercury in biological samples. Methods have been developed for the analysis of mercury in breath samples. These are based on AAS with either flameless (NIOSH 1994) or cold vapor release of the sample to the detection chamber (Rathje et al. 1974). Flameless AAS is the NIOSH-recommended method of determining levels of mercury in expired air (NIOSH 1994). No other current methods for analyzing breath were located. 

Baxter DC, Freeh W. 1990. Critical comparison of two standard digestion procedures for the determination of total mercury in natural water samples by cold vapor atomic absorption spectrometry. Anal Chim Acta 236(2) 377-3 84. 

Pineau A, Piron M, Boiteau HL, et al. 1990. Determination of total mercury in human hair samples by cold vapor atomic absorption spectrometry. J Anal Toxicol 14(4) 235-238. 

Thermal evaporation of the analyte elements from the sample has long been used in atomic spectrometry. For instance, it had been applied by PreuE in 1940 [170], who evaporated volatile elements from a geological sample in a tube furnace and transported the released vapors into an arc source. In addition, it was used in so-called double arc systems, where selective volatilization was also used in direct solids analysis. Electrothermal vaporization became particularly important with the work of L vov et al. [171] and Massmann in Dortmund [172], who introduced elec-trothermally heated sytems for the determination of trace elements in dry solution residues by atomic absorption spectrometry of the vapor cloud. Since then, the idea has regularly been taken up for several reasons. 

L vov B. V., Bayonov P. A. and Ryabchuk (1981) A macrokinetic theory of sample vaporization in electrothermal atomic absorption spectrometry, Spectrochim Acta, Part B 36 397-425. 

For each sample, total mercury eontent was first determined. This was accomplished by destraction of the sample by a mixture of HNO3/H2SO/V2O5 under reflux (60-70°) during 4 h. and subsequent cold-vapor atomic absorption spectrometry. 

For air sampling in industrial settings, personnel mercury vapor samplers rely on a hopcalite filter absorber, followed by chemical treatment and atomic absorption spectrometry (AAS) analysis. This method requires field and reagent blanks, but has a reported detection limit in the pg m range (Turner and Boggle 1993). A passive diffusion sampler has also been developed as a useful technique for mercury vapor monitoring in the atmosphere and as a personal mercury dosimeter (Kvietkus and Sakalys 1994). 

The 71-page chapter by Ihnat (1982) on Application of Atomic Absorption Spectrometry to the Analysis of Foodstuffs, adheres strictly to the goal set out by editor Cantle of providing readers with a methods compendium. It concentrates on detailed recommended procedures for various food commodities, extracted from official , recommended and other sources judged reliable by the author, for the preparation (pretreatment and treatment, e.g., decomposition) of analytical samples and standards, and the determination of 21 elements by FAAS, including hydride and cold vapor generation techniques. Price and Whiteside... 

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