Raporty IChTJ. Seria A nr 1/1996

A new Polish reference material "Oriental Tobacco Leaves" (CTA-OTL-1) for inorganic trace analysis was prepared. Fresh tobacco leaves of the variety "Oriental" were dried, ground and sieved. All precautions taken to avoid contamination of the material with metals. The next step was homogenization by mixing in a plastic drum. Preliminary homogeneity checking consisted in determining of Ca, Fe and K content by X-ray fluorescence in several subsamples taken from the drum. The material was then distributed into PE bottles. Final homogeneity testing was performed by neutron activation analysis determining Co, Cr, Fe and Rb in subsamples taken from 6 individual bottles chosen at random and comparing with the analogous results obtained on subsamples taken from one (seventh) bottle. Good homogeneity of CTA-OTL-1 at least for sample weight of 100 mg was confirmed. To assure long-term stability, the whole lot of the material was sterilized by electron beam radiation. Certification of the candidate reference material was done on the basis of world-wide interlaboratory comparison exercise in which 61 laboratories, using variuos analytical methods, participated. Data evaluation was performed using the computer program specially written for this purpose. The outlying results from the population of laboratory averages were rejected by concurrent use of the four criteria i.e. those of Dixon, Grubbs, coeficient of skewness and coefficient of kurtosis. Several criteria formulated by us were employed to decide whether the overall mean obtained as a result of data evalutation can be given the status of "recommended" or "information" value. "Recommended" (certified) values were assigned for 29 and "information" values for 11 elements, respectively.