Inter-laboratory study to determine the copper concentration in three plants from the wild flora, with the view to evaluate their potential as natural source of minerals for piglets

SUMMARY An inter-laboratory study was conducted with 7 laboratories in the field of “food / feed / soil”. The main objective of the study was an accurate determination of the copper concentration of 3 plants from the wild flora (Origanum vulgare; Vaccinium myrtillus L.; Tribulus terestris). The exact determination of the copper concentration is the first step necessary in order to evaluate the potential of these plants as natural sources of trace elements for weaned piglets. The three medicinal herbs used in our study, grow in Oltenia County, Romania. A homogeneity test was applied to the samples and they were distributed to each participant on sealed plastic bags. All laboratories accomplished ten measurements for each sample. The determination method was established by protocol, flame atomic absorption spectrometry. For the reference value we choose consensus values from three expert laboratories. The appearance frequency of the results was determined by Kernel distribution plot and the remove of the doubtful results was done by the t test. In the case of laboratories with Z score satisfactory and a Zeta score unsatisfactory the International Harmonised Protocol for the Proficiency Testing of Analytical Chemistry Laboratories offer as possible explanation of unsatisfactory Zeta score an underestimation of the uncertainty. The assigned values calculated were: Vaccinium myrtillus L. 4.54 ppm Cu; for Origanum vulgare 10.87 ppm Cu; for Tribulus Terrestris 9.12 ppm Cu