Micro-homogeneity of candidate reference materials characterized by particle size and homogeneity factor determination

The IAEA Analytical Quality Control Services (AQCS) have made available two single-cell algal materials, IAEA-392 and IAEA-393, and an urban dust, IAEA-396, to study their use for analytical sample sizes in the milligram range and below. Solid sampling Zeemans effect AAS was applied to the determination of trace elements on the bases of 10(-6)-10(-3) g amounts of the selected materials. The comparability of the mean values and the reproducibility of successive measurements is being evaluated in order to compare relative homogeneity factors for many elements in the investigated materials. From the reported results it seems that the algal materials IAEA-392 and IAEA-393 are extremely homogeneous biological materials for a number of elements with an extraordinarily sharp particle size distribution below 10(-5) m. A similar situation seems to hold for the urban dust material IAEA-396, which had been air-jet milled to a particle size distribution of around 4 x 10(-6) m. The introduction of these materials as CRMs with very small amounts needed to determine the certified concentrations will help to meet the needs of micro-analytical techniques for natural matrix reference materials.