Nineta Majcen, Monika Majer, Irena Grabec Švegl
Metrology Institute of the Republic of Slovenia (MIRS), Ljubljana, Celje, Slovenia
Paul De Bievre
Institute for Reference Materials and Measurements, EC-JRC, B-2440 Geel, Belgium
Traceability of the results of measurements of gold in precious metal
alloys by XRF is described and the role of certified reference materials
(CRMs) and reference materials (RM) explained. During the measurement process,
CRMs and RMs are used twice: in the calibration of the measuring instrument
(XRF spectrometer) and just before measuring each individual sample. Certified
reference values used in the calibration process provide “stated references”
for measurement results. Their traceability must be assured by their producer(s).
A value of a (C)RM that is measured just before each individual sample, ‘only’ has a correction function. It is not part of the traceability chain, but acts as a tool to reduce measurement uncertainty. In the uncertainty budget of the result, the uncertainty of the correction factor must be taken into account.
Metrological underpinning is realised when producers appropriately certify the values of CRMs. Evaluation of all processes that take place in the measured sample or (C)RM during the measurement, is not explicitly known due to the manufacturer’s refusal of disclosure of the certification process of the (certified) value. This leaves doubt on the ‘unbroken chain of comparisons’. The analytical community must demand this missing, but essential information from the producers.