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:

Directory of scientists: Kevin A. Francesconi
Link database: USGS: Trace-Elements and Radon in Groundwater Across the United States, 1992-2003
Material database: International Atomic Energy Agency (IAEA) - IAEA-336 Trace and Minor Elements in Lichen
Material database: RECIPE Chemicals + Instruments GmbH - ClinCal 9943 Whole blood calibrator lyophilised for trace elements LOT 310
Material database: RECIPE Chemicals + Instruments GmbH - ClinCal 9988 Urine calibrator lyophilised for trace elements
Material database: International Atomic Energy Agency (IAEA) - IAEA-A-13 Trace elements in freeze dried animal blood
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: TCLP Metals - Sandy Loam 2
Material database: National Institute of Standards and Technology (NIST) - SRM 3149
Polish selenium supplements not always labeled accurately | EVISA's News
Link database: US FDA: Selenium Regulations
Link database: DrugBank: Selenium Sulfide
Agilent is introducing the second generation of Triple Quadrupole ICP-MS system: The 8900 | EVISA's News
Material database: National Institute of Standards and Technology (NIST) - SRM 1643e - Trace Elements in Water
Material database: National Research Council of Canada (NRC - CNRC) - VITB-1: Elevated-level Multivitamin Certified Reference Material for Minerals and Vitamins
Accurate determination of arsenic and its species by internal standardization for quantification by ICP-MS | EVISA's News
Company database: PS Analytical
GC-ICP-MS: A very sensitive hyphenated system for speciation analysis | EVISA's News
Material database: NIES - National Institute for Environmental Studies - CRM 27: Typical Japanese Diet
Material database: Institute of Environmental Health Monitoring (IEHS) - GBW 09142 Selenium in Lyophilized Bovine Blood
Material database: IAEA - MEL International Atomic Energy Agency - IAEA-405 - Trace Elements and Methylmercury in Estuarine Sediment