Direct on-filter analysis of crystalline silica by quantitative infrared spectrophotometry

The direct on-filter method in quantitative infrared (IR) analysis of respirable crystalline silica was evaluated in the spectral region between 250 and 1,000 cm(-1). Particle size effect was examined in the filter and KBr methods. Methods. The IR spectra of quartz (min-u-sil 10) and cristobalite (NIST cristobalite and a well-crystallized synthetic cristobalite) were measured using a dispersive type IR spectrometer. More than 20 commercially available membrane filters were examined to find suitable filters for the quantitative analysis of crystalline silica. By using the two cristobalite samples which have different particle size distributions, their IR absorbencies were measured using filter and KBr methods. Results. Calibration curves were obtained using the specific peaks of crystalline silica, and linear relationships between sample weight and infrared absorption were confirmed for each of the curves. The particle size effect in the filter method was small when compared with the effect in the KBr method. It was considered that the packing density of particles on the tilter surface affects a reduction of the particle size effect on the quantitative infrared analysis. Conclusion. The direct on-filter method is affected to a lesser extent by the particle size effect on IR spectrometry than the conventional KBr method and could be applied to the quantitative analysis of crystalline silica in environmental and biological samples.