Speciation
Definition
Determining the chemical form of a metal in a sample, not just the total. Critical for arsenic because As(III) trivalent arsenite is 60 times more toxic than As(V) pentavalent arsenate, and methylated organic species like arsenobetaine from seafood are essentially non-toxic. Modern speciation runs by HPLC-ICP-MS.
- Field
- Forensic toxicology, trace analysis
- Key instrument
- HPLC-ICP-MS
- Toxic form example
- Arsenite As(III), roughly 60x more toxic than arsenate As(V)
- Non-toxic form example
- Arsenobetaine from seafood
- Distinguishes from
- Total elemental analysis (which does not separate forms)
Common questions
Why can total arsenic testing alone mislead a poisoning investigation?+
A high total arsenic reading can come entirely from recently eaten seafood containing non-toxic arsenobetaine, which without speciation could be mistaken for evidence of inorganic arsenic poisoning.
What error does skipping speciation risk in casework?+
It risks a false positive interpretation of exposure, since total-metal methods cannot distinguish a dangerous inorganic species from a harmless organic one, which speciation by HPLC-ICP-MS is specifically designed to resolve.
Related terms
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- Chelation Therapy
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- Marsh Test
- Sensitive 1836 method for arsenic in which the acidified sample is added to zinc and dilute sulphuric acid. The evolved arsine gas...
- Mees Lines
- Transverse white bands across the fingernails that follow acute or repeated chronic exposure to arsenic, thallium or selenium. Appear 4 to 8...
- Reinsch Test
- Classical screen for arsenic, antimony, mercury and bismuth. A clean copper strip is immersed in the acidified sample (concentrated HCl, near-boiling) for...