Any one of a group of three quantities characterizing the composition of a mixture and defined as one of mass, amount of substance (chemical amount), or number divided by volume, giving, respectively, mass, amount (of substance), or number concentrations.

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

Elephant Seals’ fur as a source for methylmercury in coastal sea water | EVISA's News
Seabass populations can be differentiated by their Mercury Isotope Distribution | EVISA's News
Material database: The Food and Environment Research Agency (FAPAS) - Test Material T0797 (Canned Fish)
Instrument database: Thermo Scientific - XVI+ Total Sulfur analyzer
Link database: iv: Stability of Elements at ppb Concentration Levels
Material database: FAPAS - Test Material T0797 (Canned Fish)
Instrument database: Prince Technologies B.V. - Lambda 1010 UV-VIS Detector
Herbal remedies may cause harm | EVISA's News
Instrument database: Bodenseewerk Perkin-Elmer GmbH - Lambda 2 Spectrophotometer
Link database: A Fresh Look at Element Distribution in the North Pacific
Decreased risk of colorectal cancer linked with higher selenium status | EVISA's News
Instrument database: Biochrom Ltd. - Libra S22 UV/VISIBLE Spectrophotometer
Side effects of cisplatin chemotherpy: Platinum speciation matters | EVISA's News
FDA Approves Chromium Claim | EVISA's News
Material database: IRMM - Institute for Reference Materials and Measurements - BCR-636 Human Blood
Material database: National Institute of Standards and Technology (NIST) - SRM 1635 - Trace Elements in Coal (Subbituminous)
Instrument database: Thermo Scientific - TSQ Quantum XLS Ultra™ GC-MS/MS
Material database: IRMM - Institute for Reference Materials and Measurements - BCR-286 - Electrolytically Refined Lead
Material database: Food Analysis Performance Assessment Scheme (FAPAS) - Test Material T07138 (Milk Powder)
EU directive 2003/53/EC on chromium in cement | EVISA's News