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Stability of Reference Materials for Elemental Speciation Analysis


Reference materials are meant to support the analyst with respect to method validation and quality control. For this reason reference materials must be "sufficiently homogenous and stable" to serve as a reference in a measurement process. The certification process leading ultimatively to a "certified reference material" (CRM) has to verify not only the content (concentration) of all certified components (elements, species) but also their homogeneous distribution as well as stability over time. Since it is not possible to extrapolate species stability from one material to another, regular stability monitoring is necessary to ensure that the certified values are still valid over the shelf-life of the CRM.  

The new study:
A group of researchers from the Institute for Reference Materials and Measurements (IRMM) in Geel (Belgium) have now summarized their experience gained during 13 years of stability monitoring of CRMs certified for metal species. The materials tested included CRMs certified for organotin (BCR-462, BCR-646, BCR-477, ERM-CE477), organomercury (BCR-580, ERM-EC580, BCR-463, BCR-464,ERM-CE464), organolead (BCR-605), and organoarsenic (BCR-627).

The materials were tested regularly for the mass fractions of certified metal species based on samples stored under normal conditions (-20°C) and on samples stored under even safer conditions ("reference stock", -70°C). Measurement frequencies ranged from yearly to every three years, based on the results from the original stability check as part of their certification. The tests were performed by external "expert laboratories" using a variety of techniques for speciation analysis (GC-ECD, GC-AFS, GC-MS, GC-ICP-MS, GC-MIP-AES, HPLC-ICP-MS).

Unfortunately, the evaluation was hampered by the high variability observed between the different laboratories.  Of all results in this study, the results of organotin measurements show the highest relative standard deviations (up to 45%). Determination of methylmercury in sediment and fish is possible with much better  precision (standard deviations of reproducibility below 5%). The accuracies of determinations of trimethyllead and organoarsenic species are slightly worse but still below 10%. Anyhow, the results of the stability studies performed by IRMM did not give any evidence of degradation of the species CRMs involved. The authors therefore conclude that, given proper processing, packaging and storage, such types of CRMs can be very stable and can be used for a long time, which is a prerequisite for usefulness and cost-efficient production.

The new study

Thomas P.J. Linsinger, Guy Auclair, Barbara Raffaelli, Andrée Lamberty, Bernd M. Gawlik, Conclusions from 13 years of stability testing of CRMs for determination of metal species, Trends Anal. Chem., 2011, doi: 10.1016/j.trac.2011.01.015

Related studies

Ph. Quevauviller, F. Ariese, New sediment reference material for the quality control of butyltin and phenyltin analysis, Trends Anal. Chem., 20/4 (2001) 207-218. doi: 10.1016/S0165-9936(01)00059-0

R. Morabito, P. Soldati, M.B. de la Calle, Ph. Quevauviller, An Attempt to Certify Phenyltin Compounds in a Mussel Reference Material, Appl. Organomet. Chem., 12 (1998) 621–634. doi: 10.1002/(SICI)1099-0739(199808/09)12:8/9<621::AID-AOC771>3.0.CO;2-Z

A. Lamberty, H. Schimmel und J. Pauwels, The study of the stability of reference materials by isochronous measurements, Fresenius' J.  Anal. Chem., 360/3-4 (1998) 359-361. DOI: 10.1007/s002160050711

Related EVISA Resources

Brief summary: Certified Reference Materials for Speciation Analysis
Brief summary: Speciation Analysis - Striving for Quality
Brief summary: Speciation and Toxicity
Brief summary: GC-ICP-MS: A very sensitive hyphenated system for speciation analysis
Brief summary: LC-ICP-MS - The most often used hyphenated system for speciation analysis
Link page: All about CRMs

Related EVISA News

  November 23, 2010: New certified reference material supporting mercury speciation analysis of blood
  February 3, 2009: New Reference Material for Hexavalent Chromium in Contaminated Soil
November 15, 2005: NIST/EPA/NJ DEP embark on the preparation of a soil reference materials for chromium speciation
August 2, 2005: New CRM for Selenomethionine in yeast developed by NRC Canada is now on the market
May 6, 2004: Reference materials producers launch new European initiative

last time modified: January 26, 2012


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