Choice of a suitable material for construction of a battelle type impactor to minimize systematic errors in sampling of airborne dust

Abstract

Systematic errors can occur when airborne dust is sampled with an impactor for subsequent element analysis. As could be shown, blank values, collection losses and memory effects are caused by the impactor and the material it is made of. Four different materials were chosen to build up a two-stage Battelle type impactor: Makrolon®, titanium, aluminium and stainless steel. The latter was applied without and with a coating of TiN. Air dust was collected on Vaseline® coated impaction plates and directly analyzed by total reflection X-ray fluorescence (TXRF). Up to 15 elements were determined simultaneously after internal standardization. Blank values arising from the impactor walls in contact with the gas flow were measured by sampling air from a clean bench. Relative collection losses were determined by sampling ambient air with two impactors in parallel and by comparing the two sets of results. Memory effects were measured by first collecting airborne particulates and then, after having replaced the impaction plates, pulling air through the impactor in a clean bench. The three effects led to relative systematic errors of a few % up to several 10% depending on element and impactor material. Stainless steel causing the largest errors has to be considered the least suitable material, even if coated with TiN. Aluminium led to moderate systematic deviations. Only titanium and Makrolon® were proven to be widely suitable impactor materials, the latter one, however, only when short sampling periods are applied.