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:

Material database: Food Analysis Performance Assessment Scheme (FAPAS) - Test Material T07157 (Tomato Paste)
Material database: JRC - Joint Research Centre - ERM-CA403 - Seawater
New arsenic species detected in carrot samples | EVISA's News
Material database: National Metrology Institute of Japan (NMIJ) - NMIJ CRM 7405-a: Trace Elements and Arsenic Compounds in Seaweed (Hijiki)
Material database: FAPAS - Test Material T07128 (Canned Fish)
Instrument database: CHEMTECH AI LIMITED - CTA 1900 Double Beam UV Spectrometer
Material database: International Atomic Energy Agency (IAEA) - IAEA-V-9 Trace Elements in Cotton Cellulose
Methylmercury in European rice varies by more than a factor of 50 | EVISA's News
Trimethylselenonium is not the major metabolite for human cancer patients excreting high doses of selenium | EVISA's News
Instrument database: Jenway - PFP7 Flame Photometer
Material database: National Institute of Standards and Technology (NIST) - SRM 2669 - Arsenic Species in Frozen Human Urine
Books and Special Issues on Elemental Speciation (published since 2011) | EVISA's News
Fractionation as a first step towards speciation analysis | EVISA's News
Link database: EFSA: Long-term dietary exposure to chromium in young children living in different European countries
Material database: RECIPE Chemicals + Instruments GmbH - ClinChek 8884 Control blood plasma, lyophilised, trace elements level II: LOT 129
Instrument database: Varian Inc. (Part A) - Vista MPX Simultaneous ICP-OES
Instrument database: Metrohm AG - MIC-1 Advanced IC System
Material database: QUASIMEME - Tributyltin-ethyl
Link database: Thimerosal - Harmless Vaccine Preservative Or Just Another Toxic Organic Mercury Compound?
Material database: International Atomic Energy Agency (IAEA) - IAEA-153 Trace Elements in Milk Powder