Results of four inter-laboratory comparisons provided by the Forensic Isotope Ratio Mass Spectrometry (FIRMS) network

Abstract 

Between 2004 and 2008 the Forensic Isotope Ratio Mass Spectrometry (FIRMS) network organised four Inter-Laboratory Camparison excercises with the aim of harmonising and validating isotopic measurements to be used for forensic applications.

The samples distributed comprised materials of potential forensic interest such as packaging and pharmaceuticals to be analysed for δ²H, δ¹³C, δ¹⁵N and δ¹⁸O composition. As many as 30 international laboratories participated in these comparisons. Results have shown overall improvements for both within- and inter-laboratory reproducibility with respect to δ¹³C and δ¹⁵N measurements.

Only a small number of laboratories returned results for δ²H and δ¹⁸O analysis and these results highlighted a need for improvement in the reproducibility of these measurements and a need to address the exchange of hydrogen between samples and ambient moisture. Results also highlighted the importance of sample preparation procedures and the need to standardise both these procedures and calibration against Standard Reference Materials. Future Inter-Laboratory Comparison exercises will assess the suitability of laboratories to submit data to national and international databases similar to those currently operated for fingerprints, DNA etc.

Keywords: Isotope ratio, Isotope ratio mass spectrometry (IRMS), Inter-laboratory comparison, Validation