Selenium analytical methods

Comprehensive accounts of the various gravimetric, polarographic, spectrophotometric, and neutron activation analytical methods have been pubHshed (1,2,5,17,19,65—67). Sampling and analysis of biological materials and organic compounds is treated in References 60 and 68. Many analytical methods depend on the conversion of selenium in the sample to selenous acid, H2Se02, and reduction to elemental selenium when a gravimetric deterrnination is desired. 

Comprehensive accounts of the analytical chemistry of teUurium have been pubUshed (5,26—30). The analytical methods for the determination of teUurium are to a considerable extent influenced by the element s resemblance, in many of its properties and in its limited terrestrial abundance, to selenium. 

Many analytical methods depend on the conversion of the tellurium in the sample to teUurous acid, H2Te02. Should teUurous acid precipitate on dilution, it can be redissolved with hydrochloric acid. Although tellurium is not as readily volatile as selenium, precautions should be taken to prevent the volatilisation of tellurium when halogen or hydrohaUde media are used during sample decomposition. 

The oxidation of teUurium(IV) by permanganate as an analytical method has been studied in some detail (26). The sample is dissolved in 1 1 nitric-sulfuric acid mixture addition of potassium bisulfate and repeated fuming with sulfuric acid volatilises the selenium. The tellurite is dissolved in 10 vol % sulfuric acid, followed by threefold dilution with water and titration with potassium permanganate ... 

Saturated solutions of some reagents (T) 829 Schoniger oxygen flask see Oxygen flask Schwarzenbach classification 53 Screened indicators 268 Sebacic acid 469 Secondary pH standards 831 Selective ion meters 567 Selectivity coefficient, 559 in EDTA titrations, 312 in fluorimetry, 733 of analytical methods, 12 Selenium, D. of as element, (g) 465 Semi-log graph paper 572 Sensitivity (fl) 834, (fu) 732 Separation coefficient 163, 196 Separations by chromatographic methods, 13, 208. 233, 249... 

The Determination of Selenium. The most difficult trace element to determine in coal by wet chemical methods is selenium. Two alternative dissolution techniques can be used—H. L. Rooks combustion method (7) and the oxygen bomb combustion method (4). Also, two alternative analytical methods can be used—the hydride evolution method (5) and the graphite furnace method. 

Special precautions are necessary during the initial preparation of soil for certain analyses, such as for boron, mercury and selenium, and details of these precautions are given in any well-written published analytical method. Any analytical method for such elements that does not include such information is not worthy of further consideration. 

A guaranteed analysis relating to certain nutrients (crude protein (CP), lysine, crude fat, crude fibre, calcium, phosphorus, sodium (or salt), selenium and zinc). A changeover from crude fibre to the more informative neutral-detergent fibre and acid-detergent fibre is planned once the analytical methods have been approved by the regulatory authorities for universal application in the feed industry. 

Advances in selenium biochemistry (Arthur, 1994 Heider and Boeck, 1994 Foster and Sumar, 1997 Patching and Gardiner, 1999) and methods for the determination and speciation of the element in biological and environmental samples (Pyrzynska, 1996 D Ullivo, 1997 Thomson, 1998) have been reviewed. In this section, a brief overview of more recent developments in analytical methods and their application to the study of selenium-containing species in biological materials is provided. 

Se° + Se2 ), as described previously. Analytical methods for speciation of selenium in water have been reviewed (Russeva and Havezov, 1996). 

M. Montes Bayon, T. D. Grant, J. Meija, J. A. Caruso, Selenium in plants by mass spectrometric techniques Developments in bio-analytical methods, J. Anal. Atom. Spectrom., 17 (2002), 1015 D1023. 

H. Chassaigne, C. C. Chery, G. Bordin, A. R. Rodriguez, Development of new analytical methods for selenium speciation in selenium-enriched yeast material, J. Chroma-togr. A, 976 (2002), 409D422. 

Arsenic is 47th and Se 70th in abundance of the 88 naturally occurring elements. Much more has become known about the distribution and behavior of arsenic and selenium in the environment since the 1980s because of the increased application of improved analytical methods such as inductively... 

Historically, analysis for selenium has been difficult, partly because environmental concentrations are naturally low. Indeed, selenium analysis still remains problematic for many laboratories at concentrations below 0.01 mg a relatively high concentration in many environments (Steinhoff et al., 1999). Hence, selenium has often been omitted from multi-element geochemical surveys despite its importance (Darnley et al., 1995). Analytical methods with limits of detection of <0.01 mgL include colorimetry, total reflectance-XRF, HG-AFS, gas chromatography... 

Pre-treatment to destroy organic matter. Organic selenium species are more widespread in the environment than comparable arsenic species. The determination of total selenium by most analytical methods requires samples to be pre-treated to remove organic matter, release selenium, and change its oxidation state. 

The environmental scientist has at his disposal a variety of sensitive, multi-elemental analytical methods that can lead to a massive amount of data on airborne metals. Optimum use of these tools for environmental monitoring calls for focusing resources only on those metals that are environmentally important. Considerations of toxicity along with their ability to interact in the air, leading to the formation of secondary pollutants, and their presence in air have led to the identification of 17 environmentally important metals nickel, beryllium, cadmium, tin, antimony, lead, vanadium, mercury, selenium, arsenic, copper, iron, magnesium, manganese, titanium, chromium, and zinc. In addition to the airborne concentration, the particle size of environmentally important metals is perhaps the major consideration in assessing their importance. 

The Element.—Analytical methods for the determination of trace quantities of selenium in two very different materials have been described. The first275 employs the use of flameless atomic absorption spectrophotometry for the direct determination of selenium (and Pb, Bi, Se, Te, and Tl) at p.p.m. levels in high-temperature alloys. The second method276 is able to determine the selenium content of plant material at levels as low as 0.005 fxg g The method involves the reaction of SeIV with 4-nitro-o-phenylenediamine to form 5-nitropiaselenol, which may be detected by means of a gas chromatograph. 

The reaction of o-phenylenediamine derivatives with quadrivalent selenium, which affords 2,1,3-benzoselenadiazoles, has been used as a very sensitive analytical method for the detection of selenium in water, food, and animal tissue. The 2,1,3-benzoselenadiazoles have also been... 

Analytical Methods for Determining Selenium in Biological Materials... 

The purpose of this chapter is to describe the analytical methods that are available for detecting, measuring, and/or monitoring selenium, its metabolites, and other biomarkers of exposure and effect to selenium. The intent is not to provide an exhaustive list of analytical methods. Rather, the intention is to identify well-established methods that are used as the standard methods of analysis. Many of the analytical methods used for environmental samples are the methods approved by federal agencies and organizations such as EPA and the National Institute for Occupational Safety and Health (NIOSH). 

The analytical methods used to quantify selenium in biological and environmental samples are summarized below. Table 7-1 lists the applicable analytical methods used for determining selenium and selenium compounds in biological fluids and tissues, and Table 7-2 lists the methods used for determining selenium in environmental samples. 

A variety of analytical methods can be used to determine trace concentrations (ng/g) of selenium in biological tissues. These include fluorometry, neutron activation analysis (NAA), atomic absorption... 

Table 7-2. Analytical Methods for Determining Selenium in Environmental Samples CO m r m z... 

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