Final certification of two new reference materials for inorganic trace analysis

Two new biological reference materials for inorganic trace analysis: Tea Leaves (INCT-TL-1) and Mixed Polish Herbs (INCT-MPH-2) were prepared and certified at the Institute of Nuclear Chemistry and Technology (INCT), Warsaw, employing the general strategy of the preparation and certification of CRMs developed in INCT. For both materials ca 40 kg of ground sieved and carefully homogenized fraction of nominal size ≤ μm was obtained. Homogeneity of materials studied by INAA was shown to be good for samples of masses m ≥ 100 mg but further investigations indicate that for most of elements these materials can be considered homogeneous down to masses of ca 5 mg or perhaps even lower. The certification was based on results of a world wide interlaboratory comparison in which 109 laboratories from 19 countries participated. The results of the analysis of a CRM, which was sent and analyzed along with intercomparison samples and the identity of which was known only to the organisers, were utilized in the process of certification. in addition selected elements were analyzed also by definitive methods based on RNAA. The content of more than 30 elements could be certified in each of the new CRMs. Analytical uncertainties and stability of uncertainties were qualified to arrive at combined uncertainties of the certified values. In addition information values were provided for some other elements. (author)