November 2014

LGC produces first material certified for carbon isotope ratios traceable to the SI

LGC has produced the first material certified for carbon isotope ratios traceable to the SI (International System of Units).

The amino acid (Glycine) reference material is certified for absolute carbon isotope ratios and will benefit food and drug testing laboratories, forensic analysts and research laboratories in the field of biogeochemistry.

The LGC team successfully developed a novel calibration strategy based on the use of gravimetrically prepared synthetic isotope mixtures from enriched carbon isotopes for the determination of absolute carbon isotope ratios by multicollector-inductively coupled plasma- mass spectrometry (MC-ICPMS).  Two technical papers describing the calibration procedure have been published in the Journal of Analytical Atomic Spectrometry [1] and Analytical and Bioanalytical Chemistry [2]. This validated method was used to produce an amino acid (Glycine) reference material certified for absolute carbon isotope ratios, which are traceable to the SI.

Dmitriy Malinovskiy, Science Leader in isotope ratio analysis, explains, “Glycine was selected as a reference material due to its relevance to both food and forensic industries, and its relative simplicity in preparation.

“Until now, reference standards for carbon isotope amount ratio values have been unavailable and existing materials are certified only in terms of so-called d13C values, relative to a reference standard that defines the VPDB scale.”  

Although the relative abundance of isotopes such as 13C and 12C was fixed when the earth was formed – and on a global scale has not changed since – the isotopic composition of a material can be subtly affected by its geographical origin, or how it has been processed or manufactured. Measurement of these small differences in isotope ratios can therefore provide information on the origin of materials.

SI traceable absolute carbon isotope ratios and the certification of reference standards underpin important industrial sectors, including pharmaceutical, fuel, food and feed, as well as aiding analytical, geochemical and forensic laboratories.

Dmitriy says, “Measurements using a reference material certified for absolute isotope ratios have particular benefit in that mass balance calculations for measurement results are significantly more accurate. Use of the reference material will therefore enhance the quality of measurements in laboratories, enabling analysts to produce traceable, comparable and reliable results.”

Glycine with certified 13C/12C isotope amount ratio traceable to the SI has now been approved by the European Reference Materials (ERM®) consortium and is the first reference material produced with SI traceable absolute carbon isotope ratios. The material, ERM®-AE672a, is available from LGC’s Standards division. LGC’s scope of accreditation for the production of reference materials to ISO Guide 34, has recently been extended to include the production of glycine characterised for the 12C /13C isotope ratio. This is reinforced by recent ISO/IEC 17025 accreditation for the measurement step.

The validation of methodologies for absolute carbon isotope ratio measurements builds on a growing key platform capability established within LGC through its role as a designated National Measurement Institute for chemical and bio-measurement. It establishes the basis for assigning values that meet the needs of UK industry and law enforcement bodies. The assignment of traceable carbon isotopic ratios to materials of interest allows assessment of measurement accuracy and helps the interested parties gain traceability to the SI for these measurands.

Phil Dunn, a researcher from the Inorganic Analysis team at LGC, will discuss the challenging measurements involved in the certification of the new isotope ratio reference material for absolute C isotope ratio traceable to the SI at the Government Chemist conference on Tuesday 25 November. The conference, ‘Beating the cheats: Quality, safety and authenticity in the food chain’ is designed to demonstrate the importance of measurement in the fight against fraud, and ensuring food authenticity and safety. Find out more at www.gov.uk/government/organisations/government-chemist

[1] D Malinovskiy ,P Dunn and H Goenaga-Infante, J. Anal. At. Spectrom., 2013, 28, 1760-1771
[2] Dunn PJ, Malinovsky D, Goenaga-Infante H. Anal Bioanal Chem. 2014, DOI: 10.1007/s00216-014-7926-1.