Lessons learned from inter-laboratory studies of carbon isotope analysis of honey.

Forensic application of carbon isotope ratio measurements of honey and honey protein to investigate the degree of adulteration with high fructose corn syrup or other C4 plant sugars is well established. These measurements must use methods that exhibit suitable performance criteria, particularly with regard to measurement uncertainty and traceability - low levels of adulteration can only be detected by methods that result in suitably small measurement uncertainties such that differences of 1‰ or less can be reliably detected. Inter-laboratory exercises are invaluable to assess the state-of-the art of measurement capabilities of laboratories necessary to achieve such performance criteria. National and designated metrology institutes from a number of countries recently participated in an inter-laboratory assessment (CCQM-K140) of stable carbon isotope ratio determination of bulk honey. The same sample material was distributed to a number of forensic isotope analysis laboratories that could not participate directly in the metrological comparison. The results from these studies have demonstrated that the majority of participants provided isotope delta values with acceptable performance metrics; that all participants ensured traceability of their results; and that where measurement uncertainties were reported; these were fit-for-purpose. A number of the forensic laboratories only reported precision rather than full estimates of measurement uncertainty and this was the major cause of the few instances of questionable performance metrics. Reporting of standard deviations in place of measurement uncertainties is common practice outside metrology institutes and the implications for interpretations of small differences in isotopic compositions are discussed. The results have also highlighted a number of considerations that are useful for organisers of similar inter-laboratory studies in the future.

Identification of the geographical place of origin of an unidentified individual by multi-isotope analysis.

A multi-isotope investigation (Sr and Pb isotopes and δ18O, δ13C and δ15N) was applied to bone and teeth from an unidentified male found drowned in the"IJ" Ruyterkade in Amsterdam, The Netherlands in March of 1999. The individual remained unidentified until mid 2013, after the isotope study was completed. Coupled δ13C and δ15N values in bone collagen recovered from rib and femur are consistent with an omnivore living in a region where C3-type diet dominates (i.e. Europe). Integrated Sr and Pb isotopes and δ18O values in canine and third molar teeth and femur and rib bone data exclude extended residence in north-west Europe and particularly The Netherlands. Characteristic Pb isotope ratios coupled with inferred δ18O values of drinking water argue for a most probable place of origin for the unidentified individual in west and south Poland, south-east Slovakia and the region of Ukraine-Romania-Bulgaria, specifically the region associated with the Carpathian Mountains. Independent of the isotope study, the Cold Case Team made a positive identification with an individual from south-west Poland, validating the results of the multiple-isotopic approach.

Development and evaluation of a standard method for the quantitative determination of elements in float glass samples by LA-ICP-MS.

Forensic analysis of glass samples was performed in different laboratories within the NITE-CRIME (Natural Isotopes and Trace Elements in Criminalistics and Environmental Forensics) European Network, using a variety of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) systems. The main objective of the interlaboratory tests was to cross-validate the different combinations of laser ablation systems with different ICP-MS instruments. A first study using widely available samples, such as the NIST SRM 610 and NIST SRM 612 reference glasses, led to deviations in the determined concentrations for trace elements amongst the laboratories up to 60%. Extensive discussion among the laboratories and the production of new glass reference standards (FGS 1 and FGS 2) established an improved analytical protocol, which was tested on a well-characterized float glass sample (FG 10-1 from the BKA Wiesbaden collection). Subsequently, interlaboratory tests produced improved results for nearly all elements with a deviation of < 10%, demonstrating that LA-ICP-MS can deliver absolute quantitative measurements on major, minor and trace elements in float glass samples for forensic and other purposes.