Radioactive Labelling of Membrane Filters for the Assay of Air-borne Material

Abstract

THE quantitative assessment of air-borne material with membrane filters is being widely employed, mainly because of their high collection, efficiency, non-hydroscopic properties and more uniform particle deposition than on other filter materials¹. Since most of the particles deposited are held at the surface², the classical methods of assessment of deposits can be-replaced or augmented by indirect methods. The latter consist, for example, in estimating the amount of deposit material by comparing stains³ with suitable-standards or by objective measurement as, for example, reflectance photometry⁴. Chemical reaction between suitably impregnated or wetted filters and aerosol droplets may also be employed with quantitative estimation of the resulting colour effects⁵.