Colorimetric Determination of Siliceous Atmospheric Contaminants

Paniculate silica and silicates are collected on membrane filters, dissolved in hydrofluoric acid, and determined colori-metrically as yellow silicomolybdate or as molybdenum blue after reduction with l-amino-2-naphthol-4-sulfonic acid. The dual sensitivity obtained by the use of the two colors permits accurate analyses in the relatively large range of 1 microgram to 2.5 milligrams without the necessity of taking an aliquot. The small air volumes required are easily sampled with hand-op-emteri equipment.