The use of certified reference materials is a key element in ensuring the comparability of results of trade partners and for providing credibility and quality assurance of measurements used as evidence in criminal proceedings. This project proposes to carry out the research and development needed to demonstrate the feasibility of producing and certified reference materials for isotope ratio measurements by GC-IRMS (gas chromatography coupled to isotope ratio mass spectrometry via a combustion interface) and EA-IRMS (elemental analyzer IRMS). No reference materials currently exist for GC-IRMS despite the fact that the number of applications for GC-IRMS has continued to increase and the technique is now used in government laboratories for the detection of adulteration in foodstuffs and of exogenous steroids illegally used by some athletes and by police forensic teams to trace distribution networks of drugs of abuse.
Of the eleven individual compounds studied, 8 were shown to be suitable as reference materials for GC-IRMS calibration. These were: 3,5,N,N-tetramethylaniline, 2,6-dimethylaniline, methyl-N-methylanthranilate, dodecane, 1-octanol, methyl decanoate, methyl dodecanoate, that were included in the mix and vanillin. The other 3 compounds showed problems either of instability, as assessed from the results of the accelerated stability tests, or of heterogeneity. A simulated certification exercise using ALL eleven compounds for EA-IRMS measurements and the mix of seven compounds for GC-IRMS determinations was carried out in which around 20 laboratories took part. The results were compiled and treated using the dedicated SoftCRM software available from a previous EU-funded project. The exercise gave good results for EA-IRMS determinations of delta 13C and delta 15N, and satisfactory results for the delta 2H determinations. The delta 18O determinations had been excluded from the project early on due to a difficulty in achieving comparable results between the consortium laboratories despite good internal repeatability.
From the data from the inter-laboratory tests, it was possible to obtain reference values for each of the eleven individual compounds for delta 13C, delta 15N and delta 2H measured by EA-IRMS and to evaluate the performance of the GC-IRMS technique compared to that of the EA-IRMS technique. This was only possible for delta 13C as too few results were available for the other parameters. From the results obtained, a set of technical data sheets were established (one per compound and one for the GC-IRMS mix) which form the basis of recommendations for the use of these compounds as future reference materials: their possibilities, usage and limits. Each technical sheet provides details of the compound name, structure, suitable packaging, storage and transport conditions. Details of the EA-IRMS parameters to be certified and associated performance data calculated from the Simulated Certification Exercise are provided. Through contact with the instrument manufacturers, an estimate of the total number of units to cover laboratory needs for 5 and 10 years, and the costs of producing such reference materials has been made. The successful production of certified reference materials using the results obtained in this project would contribute towards improved accuracy of GC-IRMS measurements. Since such compounds do not currently exist this is a major achievement of the project.
Funding SchemeCSC - Cost-sharing contracts
60439 Frankfurt Am-main