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-186 - Pig Kidney
Link database: The Globe and Mail:
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Loamy Sand 4
Thermo Sponsors Postdoctoral Position for Speciation Analysis | EVISA's News
Link database: Hazardous Substances Data Bank: Selenium dimethyldithiocarbamate
Link database: Hazardous Substances Data Bank: Selenium compounds
Tellurium Speciation Analysis of Soil Samples Taken from an Area Associated with the Storage, Processing, and Recovery of Electrowaste | EVISA's News
Exchange of sulfur against selenium makes insulin analogue last longer | EVISA's News
Link database: Austria: University of Graz, IfC, Environmental and Trace Element Analysis
Material database: National Institute of Standards and Technology (NIST) - SRM 1950 - Metabolites in Human Plasma
Chemical speciation analysis for life science | EVISA's News
Link database: Selenium and its Relationship to Cancer
Species of interest
New Packaging Solution Reduces Mercury Content in Tuna | EVISA's News
Material database: JRC - Joint Research Centre - BCR-032 - Trace elements in Moroccan phosphate rock
Material database: IRMM - Institute for Reference Materials and Measurements - BCR-279 Sea lettuce
Instrument database: Analytik Jena GmbH - contrAA® 800 F - HRCS- Atomic absorption spectrometer for flame and hydride techniques
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: Trace Metals - Fresh Water Sediment 3
Material database: Sigma-Aldrich - Matrix CRM - Soil, Sludge, Sediment: TCLP Metals - Loam 1
Experts in Speciation Analysis came together in Münster, September 4-7, 2007: Part 2 | EVISA's News