Cold vapor-atomic absorption spectroscopy

Atomic absorption spectroscopy is more suited to samples where the number of metals is small, because it is essentially a single-element technique. The conventional air—acetylene flame is used for most metals however, elements that form refractory compounds, eg, Al, Si, V, etc, require the hotter nitrous oxide—acetylene flame. The use of a graphite furnace provides detection limits much lower than either of the flames. A cold-vapor-generation technique combined with atomic absorption is considered the most suitable method for mercury analysis (34). 

Another test method for the determination of mercury in coal (ASTM D-6414) involves (method A) solubilizing of the mercury in the sample by heating the sample at a specified temperature in a mixture of nitric and hydrochloric acids. The acid solutions produced are transferred into a vessel in which the mercury is reduced to elemental mercury. The mercury vapor is determined by flameless cold-vapor atomic absorption spectroscopy. An alternative method (method B) involved solubilization of the mercury by heating the sample in a mixture of nitric acid and sulfuric acid with vanadium pentoxide. The acid solution is then transferred into a vessel in which the mercury is reduced to elemental mercury. The mercury content is determined by flameless cold-vapor atomic absorption spectroscopy. However, mercury and mercury salts can be volatilized at low temperatures, and precautions against inadvertent mercury loss should be taken when using this method. 

In EMEP, ICP-MS is dehned as the reference technique. The exception is mercury, where cold vapor atomic fluorescence spectroscopy (CV-AFS) is chosen. Other techniques may be used, if they are shown to yield results of a quality equivalent to that obtainable with the recommended method. These other methods include graphite furnace atomic absorption spectroscopy (GF-AAS), flame-atomic absorption spectroscopy (F-AAS), and CV-AFS. The choice of technique depends on the detection limits desired. ICP-MS has the lowest detection limit for most elements and is therefore suitable for remote areas. The techniques described in this manual are presented with minimum detection limits. Table 17.2 lists the detection limits for the different methods. 

Outline of Method. A sample is weighed into a beaker, dissolved in benzene 2-propanol, and burned in an oxy-hydrogen flame using a Wickbold combustion apparatus. The combustion products are collected in a 5% sulfuric-nitric acid mixture containing potassium permanganate. Prior to measurement, trapped mercuric salts are reduced to elemental mercury with tin (II) chloride. The mercury is then swept out of solution and measured by cold-vapor atomic absorption spectroscopy. 

The mercury removal performance of pilot-scale ICDAC and of Norit s FGD carbon were determined in a 0.236 m% (0.25 MWe) pilot plant operated by CONSOL, Inc., Library, PA. The pilot plant can simulate flue gas conditions downstream of the air preheater in a coal fired utility power plant. The flue gas mercury concentration studied (10-15 pg/m ) is typical of utility flue gas concentration. Mercury removals were evaluated in the flue gas duct, which provided a gas residence time of approximately 2 seconds, and in the baghouse, where the solids retention times can be as long as 30 min. Common test conditions were flue gas flow, 0.165 m /s flue gas wet bulb temperature, 50-53°C flue gas composition, 1000 ppmv dry SO2, 10 vol% dry O2, and 10 vol% dry CO2. All tests were conducted with a fly ash obtained from a coal-fired utility boiler firing an eastern bituminous coal. The fly ash feed rate was 4.5 kg/hr (solids loading of 90.6-104.7 gm/dcm ). Mercury removal was determined from the mercury feed rate, the solids (carbon and fly ash) feed rate, and mercury analysis of the feed and recovered solids (by combustion followed by cold vapor atomic absorption spectroscopy). Except where noted, all mercury removal results discussed in this paper include mercury removal by the carbon sorbent and the fly ash. A more detailed description of the pilot test unit is given elsewhere (27]. 

The method which has demonstrated to be most successful one for mercury determination within natural waters is that called cold vapor-atomic absorption spectroscopy (CVAAS), which can be used with a preconcentration step [337-339] or without it [340-342], In addition, the use of continuous-flow systems for Hg CV generation has also been reported [343-345]. 

M. A. Dominguez, M. Grunhut, M. F. Pistonesi, M. S. Di Nezio and M. E. Centurion, automatic flow-batch system for cold vapor atomic absorption spectroscopy determination of mercury in honey from argentina using online sample treatment, J. Agric. Food Chem., 2012, 60(19), 4812-4817. 

Amalgamation in a gold trap is also employed in environmental analysis of organic mercury compounds such as methyl mercury. The mercury is commonly determined by cold vapor atomic absorption spectroscopy. 

Acid digestion or extraction, atomic absorption spectrometry (flame, cold vapor, hydride generation, and electrothermal), emission spectroscopy (plasma and flame), spectrophotometry, anodic stripping voltametry... 

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