The most critical effect is when the particle size distribution of the analytes does not match the material used for calibration. No certified standards are available for bulk calibration, and it will probably be difficult to create any because of the variability of samples to be analyzed. Several standard methods have been established by federal agencies for respirable silica. Individual companies and analytical service laboratories have set up and tested procedures for bulk analyses for specific types of samples. Modern diffraction instrumentation is adequate for the measurements to be performed.
Computerized instruments allow the data to be digitized for easy mathematical processing.
Data collection parameters are flexible and usually defined by the amount of silica in the sample. Longer count times are needed for smaller amounts to maintain the statistical significance of the measurements. Step size and scan range are less important except when there are peak interferences which require more of the diffraction pattern to be measured. Several studies are warranted to improve the current status of diffraction analysis for the quantification of crystalline silica. Additional standards need to be certified in sufficient quantities to supply needs for many years.