Isotope metrological traceability

Note that even if we are to adopt a more fitting discrimination law for the double-spike calculus, we still have to accept the equality of the discrimination functions between the isotopes of the same element - an assumption that is now shown experimentally to be incorrect [17]. To date, this remains the breaking point in the chain of metrological traceability for double-spike calibration results. 

Andreis E, Kiillmer K, Appel M (2014) Applieation of the reference method isotope dilution gas chromatography mass spectrometry (ID/GC/MS) to establish metrological traceability for caUbration and control of blood glucose test systems. J Diabetes Sei Teehnol 8(3) 508-515... 

Table 2 Comparison of Cholesterol Reference Method Laborato- tute, NIST National Institute of Standards and Technology (US ry Network (CRMLN) traceability model to the International Or- NMI), IDMS isotope dilution mass spectrometry, ACL accredited ganization for Standardization (ISO) model. BIPM International calibration laboratory, AK Abell-Kendall Bureau of Weights and Measures, NMI National Metrology Insti-...

Chemical amount of substance or concentration measurements are ideally traceable to the mole as a common reference (see the definition of metrological trace-ability to a measurement unit). Isotope ratios do not have a unit when the amount of the individual isotopes in the ratio is expressed in the same unit (e.g., mol mok ). In an ideal situation, isotope (amount) ratio measurements should be traceable to an isotopic reference material that has been calibrated against a synthetic isotope mixture. In this case, measurements can be made traceable to the SI unit. Since this is a rare case, most isotope amount ratio measurement are only traceable to the corresponding delta 0 reference material (see also Chapter 6). In the case of delta isotope measurements, the traceability chain ends at the delta unit which is and multiples or fractions thereof. Therefore, the reference (the delta 0 reference solution) used for the delta calculations caimot be used for traceability purposes (27). 

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