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: IRMM - Institute for Reference Materials and Measurements - BCR-032 - Trace elements in Moroccan phosphate rock
Material database: National Analysis Center for Iron & Steel (NACIS) - NCS ZC73013 - Trace Elements in Spinach
Material database: JRC - Joint Research Centre - BCR-182 - Steam coal
EVISA Brfief Summary: The role of elemental speciation in legislation
Material database: RECIPE Chemicals + Instruments GmbH - ClinChek 8848 Urine Control lyophilised / trace elements level II: LOT 923
Material database: Canadian Certified Reference Materials Project (CCRMP) - CUPD-1 Copper Anode
2004 Winter Conference on Plasma Spectroscopy | EVISA's Agenda of Events
Material database: IRMM - Institute for Reference Materials and Measurements - BCR-280R - Lake sediment
Journals database: Phosphorus, Sulfur, and Silicon and the Related Elements
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Loamy Sand 2
Instrument database: GBC Scientific Equipment Ltd. - 908AA Atomic Absorption spectrophotometer
Special issue on "Advances in speciation techniques and methodology" available | EVISA's News
Material database: RECIPE Chemicals + Instruments GmbH - ClinCal 9988 Urine calibrator lyophilised for trace elements: LOT 432
Determination of the naturally occurring vanadium-complex amavadin in the fly agaric mushroom with HPLC-ICP-MS | EVISA's News
Material database: National Institute of Standards and Technology (NIST) - SRM 1632c - Trace Elements in Coal (Bituminous)
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Fly Ash 3
Link database: The Globe and Mail: Selenium levels in fish raise concerns about pollution from Red Chris mine
Material database: RECIPE Chemicals + Instruments GmbH - ClinCal 9982 Serum calibrator lyophilised for trace elements LOT 243
Material database: National Institute of Standards and Technology (NIST) - SRM 1598a - Inorganic Constituents in Animal Serum
Material database: LGC Ltd. - ERM-BC210a - Wheat Flour - Selenium and Selenomethionine