Quantitative determination of crystalline silica in respirable-size dust samples by infrared spectrophotometry

Abstract

A direct differential scanning infrared spectrophotometric method is described for the determination of crystalline silica in respirable-size atmospheric dust samples from a wide range of industrial environments. The test atmosphere is drawn through a cyclone elutriator, fitted with a membrane filter, at 1.9 l min^–1 for, typically, 1–4 h. The filter, without further preparation, is scanned from 1500 to 400 cm^–1 and the atmospheric concentration of crystalline silica determined from the intensity of the quartz (799, 780 and 695 cm^–1), together with, when present, cristobalite (796 and 621 cm^–1) absorption bands. Generation of standard crystalline silica atmospheres using a portable dust chamber is described. The effect of particle size variation on the absorbance intensity, together with sample re-radiation and mineral interference effects, are examined.