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