Energy-Dispersive X-Ray Fluorescence (EDXRF) is a cheap non-destructive technique to measure metal and mineral content, typically operated as a laboratory benchtop method.
In this study (open access), researchers at the European Commission Joint Research Centre used market samples of oregano that had been previously tested under the EU co-ordinated official control plan to investigate whether EDXRF could be used as a screening technique. This was a serendipitous extension of the use of EDXRF for checking compliance with EU limits for copper contamination. After a relatively simple sample preparation, they measured a panel of 36 metals and minerals.
They found that, at it simplest level, the ratio of copper-to-zinc was a good indicator of adulteration with olive leaves without any need for modelling statistics. Once multivariate statistics were used, samples could also be classified by geographic origin. This classification required 2-stage modelling (SIMCA then PLS-DA) to achieve full potential, and then was limited because the reference dataset was not sufficiently comprehensive in terms of countries of origin.
The researchers concluded that their work demonstrates that EDXRF is a suitable screening method to detect oregano adulteration with other species, and to authenticate the geographical origin of the product. The method is clean, cheap and has a high sample throughput because it does not require sample digestion. For those reasons, the approach is ideal to be used by control laboratories.
SIMCA allowed the authentication of the geographical origin of oregano. The performance of the authentication could be improved with a combination of SIMCA with PLS-DA that provides sensitivities and specificities higher than 90 %. However, a database well populated with results obtained with samples coming from all the main producing countries, would be needed.
