A comparison of international silica (alpha-quartz) calibration standards by Fourier-Transform Infrared Spectrophotometry

Seven international silica (alpha -quartz) standards were examined for rela tive 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 s tandards were determined by Coulter Counter to be broadly similar with equi valent spherical volume median diameter ranging between 1.2 and 3 mum. The results showed the standards to differ by as much as 30% in relative pu rity. Consequently, an internationally agreed upon calibration standard is urgently needed. Min-U-Sil 5 based NIST-SRM 1878 or Sikron F-600 are the tw o most likely candidates. Any agreed standard must have a well characterize d size distribution and closely match the respirable dust criteria. It shou ld also be studied by both infrared spectrophotometry and X-ray diffraction techniques. (C) 2001 British Occupational Hygiene Society. Published by El sevier Science Ltd. All rights reserved.