Fresh tobacco leaves of the variety "Virginia" grown in Bulgaria were hand-picked, dried, comminuted and sieved in conditions preventing contamination with metals. The material was then homogenized by mixing in a plastic drum. After preliminary homogeneity testing (XRF) the material was distributed into PE bottles. Extensive homogeneity testing by neutron activation analysis revealed, that CTA-VTL-2 can be considered homogeneous for sample size of single milligrams. To assure long-term stability the whole lot of the material was sterilized by electron beam radiation. Certification of the candidate reference material was based on the world-wide interlaboratory comparison in which 60 laboratories from 18 countries, participated using various analytical methods and techniques. Data evaluation was performed by means of software package SSQC. Several criteria were also employed to decide whether the overall mean can be given the status of recommended (certified) or information value. "Recommended" values were assigned for 33 and "information" values for 10 elements, respectively. The validity of certified values was confirmed for several elements using "very accurate methods” developed in this Laboratory. Recommended values are assigned for:
As, Ba, Br, Ca, Cd, Ce, Cl, Co, Cr, Cs, Cu, Fe, Hf, Hg, K, La, Li, Mg, Mn, Mo, Ni, P, Pb, Rb, Sb, Sm, Sr, Tb, Th, U, V, W, Zn;
Information values are assigned for:
Al, Eu, Na, S, Sc, Se, Si, Ta, Ti, Yb.
|
