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Speciation vs Fractionation



IUPAC has defined the terms used related to elemental species:

  1. Chemical species. Chemical elements: specific form of an element defined as to isotopic composition, electronic or oxidation state, and/or complex or molecular structure.
  2. Speciation analysis. Analytical chemistry: analytical activities of identifying and/or measuring the quantities of one or more individual chemical species in a sample.
  3. Speciation of an element; speciation. Distribution of an element amongst defined chemical species in a system.

    and also clearly differentiated "speciation analysis" from fractionation:

  4. Fractionation. Process of classification of an analyte or a group of analytes from a certain sample according to physical (e.g., size, solubility) or chemical (e.g., bonding, reactivity) properties.

Authors should use this terminology in order not to mislead readers of their work.  Especially misleading are statements of having determined elemental species such as hexavalent chromium when actually only a leachable chromium fraction was determined. It was shown scientists using true speciation analysis based on LC-ICP-MS that chromium fractions in foodstuffs obtained by alkaline leaching do not contain any Cr(VI).

Studies showing the absence of Cr(VI) in foodstuffs:

Fanny Hernandez, Fabienne Séby, Sandrine Millour, Laurent Noël, Thierry Guérin, Optimisation of selective alkaline extraction for Cr(VI) determination in dairy and cereal products by HPIC–ICPMS using an experimental design, Food Chem., 214 (2017) 339–346. doi: 10.1016/j.foodchem.2016.07.099

Véronique Vacchina, Inmaculada de la Calle, Fabienne Séby, Cr(VI) speciation in foods by HPLC-ICP-MS: investigation of Cr(VI)/food interactions by size exclusion and Cr(VI) determination and stability by ion-exchange on-line separations, Anal. Bioanal. Chem., 407 (2015) 3831–3839. doi: 10.1007/s00216-015-8616-3

Breda Novotnik, Tea Zuliani, Janez Scancar, Radmila Milačič, Chromate in food samples: an artefact of wrongly applied analytical methodology?, J. Anal. At. Spectrom., 28 (2013) 558-566. DOI: 10.1039/c3ja30233d

Related information

Douglas M. Templeton, Hitomi Fujishiro, Terminology of elemental speciation – An IUPAC perspective, Coord. Chem. Rev., 352 (2017) 424-431. DOI: 10.1016/j.ccr.2017.02.002

D.M. Templeton, F. Ariese, R. Cornelis, L.-G. Danielsson, H. Muntau, H.P. van Leeuwen, R. Lobinski, IUPAC Guidelines for Terms Related to Speciation of Trace Elements, Pure Appl. Chem., 72/8 (2000) 1453-1470. DOI: 10.1351/pac200072081453

 Related EVISA Resources

 Link Database: Methods for chromium speciation analysis

Brief summary: Speciation as a discipline in Analytical Chemistry - Definitions
Brief summary: Fractionation as a first step towards speciation analysis
Brief summary: ICP-MS: A versatile detection system for trace element and speciation analysis

Brief summary: LC-ICP-MS - The most often used hyphenated system for speciation analysis 

Related EVISA News

August 24, 2016: New sensitive method for chromium speciation analysis: No hexavalent chromium in dairy and cereal products
April 26, 2016: Hexavalent chromium in food ?
March 14, 2013: Chromate in food samples: an artefact of wrongly applied analytical methodology

last time modified: February 15, 2018


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