Annals of Occupational Hygiene Advance Access originally published online on June 16, 2009
Annals of Occupational Hygiene 2009 53(6):639-649; doi:10.1093/annhyg/mep038
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An International Comparison of the Crystallinity of Calibration Materials for the Analysis of Respirable 
-Quartz Using X-Ray Diffraction and a Comparison with Results from the Infrared KBr Disc Method
1 The Health and Safety Laboratory, Harpur Hill, Buxton SK17 9JN, UK
2 Institut National de Recherche et de Sécurité, Avenue de Bourgogne BP No. 27, 54501 Vandoeuvre Cedex, France
3 Institut de recherché Robert-Sauvé en santé et en sécurité du travail, 505, Boul. De Maisonneuve Ouest, Montréal, Québec H3A 3C2, Canada
4 Instituto Nacional de Silicosis, C/Dr Bellmunt S/N, 33006 Oviedo, Spain
5 National Institute for Occupational Safety and Health, 4676 Columbia Parkway, MS R-7, Cincinnati, OH 45226, USA
6 Elkem Materials R&D, PO Box 8126, Vaagsbygd, 4675 Kristiansand, Norway
* Author to whom correspondence should be addressed. Tel: +01298 218554; fax: +01298 218505; e-mail: Peter.Stacey{at}hsl.gov.uk
It is important that analytical results, produced to demonstrate compliance with exposure limits are comparable, to ensure controls are monitored to similar standards. Correcting a measurement result of respirable 
-quartz for the percentage of crystalline material in the calibration dust is good analytical practice and significant changes in the values assigned to calibration materials will affect the interpretation of results by an analyst or occupational hygiene professional. The reissue of the certification for the quartz reference material NIST 1878a in 2005 and differences in comparative values obtained by other work created uncertainty about the values of crystallinity assigned to national calibration dusts for -quartz. Members of an International Organization for Standardization working group for silica measurement ISO/TC146/SC2/WG7 collaborated to investigate the comparability of results by X-ray diffraction (XRD) and to reach a consensus.
This paper lists the values recommended by the working group for use with XRD analysis. The values for crystallinity obtained for some of the materials (NIST 1878, Min-U-Sil5 and A9950) were 6–7% lower than the original certification or estimates reported in other comparisons. Crystallinity values obtained by XRD gave a good correlation with BET surface area measurements (r2 = 0.91) but not with mean aerodynamic particle size (r2 = 0.31). Subsamples of two of the materials (A9950 Respirable and Quin 1 Respirable) with smaller particle size distribution than their parent material did not show any significant change in their values for crystallinity, suggesting that the area XRD measurement of these materials within the particle size range collected is more dependent on how the quartz is formed geologically or how it is processed for use. A comparison of results from laboratories using the infrared (IR) and KBr disc method showed that this method is more dependent than XRD on differences in the particle size within the respirable size range, whereas the XRD values were more consistent between the different measurement values obtained on each material. It was not possible to assign a value for percentage purity to each material for users of IR analysis.
This work suggests that differences are likely to exist between the results from XRD and IR analysis when measuring ‘real’ workplace samples and highlights the importance of matching the particle size of the calibration material to the particle size of the workplace dust for measurements of crystalline quartz.
Keywords: analysis • crystallinity • infrared • quartz • silica • x-ray diffraction
Received November 10, 2008; in final form April 8, 2009