A comparison of international silica (Î±-quartz) calibration standards by Fourier transformâinfrared spectrophotometry
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Seven international silica (alpha-quartz) standards were examined for relative purity to the US National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 1878 Respirable alpha-quartz by Fourier Transform-Infrared Spectrophotometry (FT-IR). The standards examined have been used in North America, the UK, Australia and Germany. The 189 samples analyzed included NIST-SRM 1878, Min-U-Sil 5, Ottawa Silica Sand, Sikron F-600, A9950 (AUST 1), DQ12-Robock, DQ12-Bergbau. Size distributions of the standards were determined by Coulter Counter to be broadly similar with equivalent spherical volume median diameter ranging between 1.2 and 3 microm. The results showed the standards to differ by as much as 30% in relative purity. Consequently, an internationally agreed upon calibration standard is urgently needed. Min-U-Sil 5 based NIST-SRM 1878 or Sikron F-600 are the two most likely candidates. Any agreed standard must have a well characterized size distribution and closely match the respirable dust criteria. It should also be studied by both infrared spectrophotometry and X-ray diffraction techniques.
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