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-664
Material database: RECIPE Chemicals + Instruments GmbH - ClinCal 9985 Plasma calibrator lyophilised for trace elements: LOT 317
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Sandy Loam 7
Material database: RECIPE Chemicals + Instruments GmbH - ClinCal 9988 Urine calibrator lyophilised for trace elements: LOT 122
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Fresh Water Sediment 2
Experts in Speciation Analysis came together in Münster, September 4-7, 2007: Part 3 | EVISA's News
Company database: Aqua Metrology Systems, Ltd.
A new study finds: Inorganic mercury stays in the brain for years if not decades | EVISA's News
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Fresh Water Sediment 2
Material database: RECIPE Chemicals + Instruments GmbH - ClinChek 8847 Urine Control lyophilised / trace elements level I_ LOT 122
Material database: National Institute for Minamata Disease (NIMD) - NIMD-1 Human Hair
Material database: National Research Council of Canada (NRC - CNRC) - HISS-1 Marine Sediment Reference Materials for Trace Metals and other Constituents
ISTERH 2015: Recent Advances in Trace Element Research in Health and Disease | EVISA's Agenda of Events
Material database: National Institute of Standards and Technology (NIST) - SRM 1640a - Trace Elements in Natural Water
Chemical speciation analysis for the life sciences | EVISA's News
Link database: National Research Council: Selenium in Nutrition
Material database: RECIPE Chemicals + Instruments GmbH - ClinChek 8848 Urine Control lyophilised / trace elements level II
Trace element speciation analysis for environmental sciences | EVISA's News
Material database: JRC - Joint Research Centre - BCR-288 - Lead with added impurities
Material database: National Research Council of Canada (NRC - CNRC) - HIAS-1 High Purity Arsenic Certified Reference Material for Arsenic Mass Fraction and Elemental Impurities