Selenium sampled: Graphite furnace atomic absorption spectrometry

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  • Published: Jun 1, 2017
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Micronutrient

Continuous sample drop flow microextraction coupled with iridium-modified tube graphite furnace atomic absorption spectrometry (GFAAS) offers a new, highly sensitive technique for measuring the trace element selenium in blood samples.

Continuous sample drop flow microextraction coupled with iridium-modified tube graphite furnace atomic absorption spectrometry (GFAAS) offers a new, highly sensitive technique for measuring the trace element selenium in blood samples.

Selenium is a non-metal, a chalcogen, group 16 of the periodic table sandwiched between sulfur and tellurium with properties intermediate between those two elements. It is toxic in large doses but considered an essential micronutrient animal health. That said whether or not it is possible to be deficient in this element is not known because it was for many years almost impossible to determine the body's load and requirements.

The element is now known to be critical to the functioning of various enzymes including the glutathione peroxidase family of enzymes (GSH-Px) which catalyse the removal of reactive oxygen species, such as hydrogen peroxide and organic hydroperoxides. The element is also critical to thyroid function with that eponymous gland and every cell that uses thyroid hormone requiring the presence of selenium as it is a cofactor for the three of the four known thyroid hormone deiodinases, which activate and then deactivate thyroid hormones and their metabolites.

Toxic challenge

Reza Akramipour, Mitra Hemati, Nazir Fattahi, Meghdad Pirsaheb, and Toraj Ahmadi-Jouibari of Kermanshah University of Medical Sciences, in Kermanshah, Iran, point out that there is a fine line between micronutrient and poison. Excess selenium leads to selenosis, symptoms of which include gastrointestinal upset, "garlic breath", fatigue, irritation of the eyes and loss of teeth, hair, and nails, mild nerve damage, cirrhosis, paralysis, liver cancer. Oxidation state and organic ligands are also often the difference between toxic and non-toxic selenium.

Atomic absorption spectrometry (AAS), UV-Vis spectrophotometry, X-ray fluorescence spectrometry, and voltammetry are commonly used in selenium determination, but the development of a simple, rapid and sensitive method for the speciation of inorganic selenium, which is often associated with greater toxicity and than organoselenium compounds remains a challenge in analytical science.

Pre-concentration

The team explains that, "The isolation and pre-concentration of selenium is a critical step for its determination in biological samples." Adding that, "The complexity of biofluids, due to the large number of exogenous and mainly endogenous compounds, may hinder method selectivity." As such, the team has turned to a novel microextraction technique, termed continuous sample drop flow microextraction (CSDFME), which was reported in Talanta in 2014 (vol 129, pp 309-314, Moinfar et al.). This method can overcome some of the difficulties associated with current techniques for analysing selenium in biological samples. The Kermanshah team has now used CSDFME for the extraction and pre-concentration of selenium(IV) and selenium(VI) species in children's blood prior to GFAAS determination of the element.

The team describes their successful application of CSDFME coupled with GFAAS in the Journal of Pharmaceutical and Biomedical Analysis and describe it as simple and inexpensive and environment friendly because it requires no organic dispersive solvent. The researchers achieved linear calibration over the range 0.06 to 3.0 micrograms per litre and a detection limit of 0.020 micrograms per litre. They suggest that the analysis of children's blood samples as a proof of principle might also be useful in research into this micronutrient.

Related Links

J Pharm Biomed Anal 2017, online: "Optimization of a new methodology for trace determination of elements in biological fluids: Application for speciation of inorganic selenium in children’s blood"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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