Between-bottle homogeneity test of new certified reference materials employing wavelength dispersive X-ray...

A pilot study has being carried out at our laboratories, with international collaborators, to develop seven certified reference materials (CRMs), which have matrices of mainly soil and biological tissues. The CRMs will be certified for macro-, micro- and trace elements for environmental, toxicological, agronomic and nutritional purposes. Homogeneity of element concentrations is a critical step in the production process of CRMs. This work employs wavelength dispersive X-ray fluorescence spectrometry (WD-XRF) to test between-bottle homogeneity of the CRMs.

The relative standard deviation (RSD), relative average deviation, Skewness and Kurtosis of element contents in seven bottles out of 80 bottles of each CRM were considered to assess homogeneity in terms of variability and distribution. More than 50% of the number of quantified elements recorded RSD between 2 and 5%. Hence, based on an in-house classification, the intended CRMs recorded excellent to good between-bottle homogeneity. Nevertheless, the contents of some elements (Ni, Rb, Zn and Br) experienced high RSD values (> 10%). The Skewness and Kurtosis values of most elements are around one indicating symmetric distribution and thus have an absence of tailing relative to the normal distribution.

WD-XRF provides fit for purpose data for assessment of initial between-bottle homogeneity in terms of rapidity, ease of use, multi-element quantification and sample non-destruction.