selenium

Selenium is a chemical element with atomic number 34, with the chemical symbol Se. Selenium occurs only rarely in the free state in nature. It is a nonmetal that is chemically related to sulfur and tellurium. It is toxic in large amounts, but trace amounts of it, forming the active center of certain enzymes such as glutathione peroxidase(GSH-Px), are necessary for the function of all cells in (probably) all animals. Selenium requirements in plants differ by species, with some plants apparently requiring none.

Isolated selenium occurs in several different forms, but the most stable of these is a dense purplish-gray semimetal (semiconductor) form that is structurally a trigonal polymer chain. It conducts electricity better in the light than in the dark, and is used in photocells (see allotropic section below). Selenium also exists in many nonconductive forms: a black glass-like substance, as well as several red crystalline forms built of eight-membered ring molecules, like its lighter cousin sulfur.

Selenium is found in economic quantities partially replacing sulfur in sulfide ores such as pyrite. Minerals that are selenide or selenate compounds are also known, but all are rare.



The term "selenium" was found in the following pages:

Material database: National Institute of Standards and Technology (NIST) - SRM 1950 - Metabolites in Human Plasma
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Sandy Loam 8
Link database: USGS: Trace-Elements and Radon in Groundwater Across the United States, 1992-2003
Directory of scientists: Oto Mestek
Material database: IRMM - Institute for Reference Materials and Measurements - ERM-BD150: Skimmed milk powder
Material database: IRMM - Institute for Reference Materials and Measurements - BCR-182 - Steam coal
Material database: The Food and Environment Research Agency (FAPAS) - Test Material T1861 (Energy drink)
Material database: IRMM - Institute for Reference Materials and Measurements - BCR-186 - Pig Kidney
Accurate determination of arsenic and its species by internal standardization for quantification by ICP-MS | EVISA's News
Experts in Bioimaging came together in Münster, May 24-25, 2018 | EVISA's News
Simultaneous selenium and sulfur speciation analysis in cultured mushrooms (Pleurotus pulmonarius) | EVISA's News
Selenium species are partly converted during their enzymatic extraction from biological samples with protease XIV | EVISA's News
Essentiality of selenium for brain development | EVISA's News
ICCST-11: 11th International Conference on the Chemistry of Selenium and Tellurium | EVISA's Agenda of Events
Directory of scientists: Alfredo Sanz-Medel
EU approves new selenium compound for use as a nutritional supplement in animals | EVISA's News
New selenium metabolites found in human serum | EVISA's News
Selenomethionine shows promising results as a protective agent against Esophageal Cancer | EVISA's News
Company database: Aqua Metrology Systems, Ltd.
Thermo Electron and Pau University Establish New Center of Excellence for Elemental Speciation Analysis | EVISA's News