Cristobalite or Opal? A Confirmation of XRD Determination using FTIR E. Stuber, J. Cole, D. MacDuff, Galson Laboratories, E. Syracuse, NY

Introduction Results • Cristobalite and quartz, both crystalline silica polymorphs and Group 1 human Initial XRD Result Compared to Result after Mineral Transfer to IR Filter, carcinogens, are regulated in the workplace by OSHA. IR Method • Crystalline silica, SiO , in workplace air can be analyzed by x-ray diffraction (XRD) methods, NIOSH 75002 and OSHA ID-142. Detection Limit Average % Recovery for Seven Replicates at 100 μg

• Quartz can also be analyzed by an infrared spectroscopy (IR) method, NIOSH 7603. Cristobalite, Seven Replicates Quartz Redeposits Cristobalite Redeposits Cristobalite Redeposits Quartz, Cristobalite Combined Redeposits • Cristobalite can be challenging to determine due to its tendency for peak broadening and 120 120 120 140 120 120 the similarity of its diffraction pattern to opal. 100 100 100 100 Cristobalite Cristobalite Cristobalite Quartz Cristobalite Method Primary Peak Secondary Cristobalite Cristobalite • Opal is not classified as a carcinogen. Results Quartz Cristobalite 100 Results Results Method Detection Results Peak Results Quartz 80 80 XRD = Results 80 Primary Peak 80 XRD = @ IR Detection Limit XRD = XRD = Cristobalite Quartz Results % % 109% % % % 102% Secondary • NIOSH 7603 was modified to include analysis of cristobalite by IR to confirm XRD @ IR = Results Secondary Results @ IR Limit 110% 80 125% cv = Peak = Recovery Secondary Recovery cv = 96% Recovery IR = Recovery Peak Results Recovery XRD = Primary results. Mineral dust from the XRD filter is redeposited on the IR filter and analyzed by @ Primary cv = cv = 102% 0.009 108% 60 Peak = 60 0.040 cv = 60 93% IR = 60 Peak = Peak = 0.040 0.026 cv = cv= 0.096 cv = 101% 105% IR. 30 μg 50 μg 60 0.030 0.149 0.026 cv = Average Average cv = -1 40 40 40 40 0.180 • Cristobalite may be quantitated on the IR at its primary peak at ~798 cm and its Recovery Recovery 0.182 40 -1 100% 107% secondary peak at ~623 cm . cv = cv = 20 0.131 20 20 20 • Quartz, cristobalite, opal, and amorphous silica all share the same primary peak on the 0.072 20 IR. Cristobalite may be determined by its secondary peak in the presence of those interferences. 0 0 0 0 0 Crystalline Silica Methods Sample 1: Workplace Sample 2: Bulk Sample Sample 3: Workplace

Method NIOSH 7500 OSHA ID-142 NIOSH 7603 NIOSH 7602 Air Sample With Quartz Air Sample Instrument XRD XRD IR IR Silica Quartz Quartz Quartz in Coal Quartz Polymorph Cristobalite Cristobalite Mine Dust Cristobalite Quartz SRM 1878A SRM 1878A SRM 1878A SRM 1878A Standard Cristobalite SRM 1879A SRM 1879A SRM 1879A SRM 1879A Standard Analytical Redeposition on Redeposition on Redeposition on Press into KBr Preparation silver membrane filter silver membrane filter acrylic copolymer pellet filter Methodology The XRD results were 330 μg at the • The calibration curves for the primary and secondary cristobalite peaks were plotted The XRD results were 62 μg at Quartz The XRD results were 400 μg at the primary angle, and 231 μg at the following NIOSH 7603 for Quartz. primary, 42 μg at Cristobalite primary, and primary angle, and 434 μg at the secondary angle after a 2x dilution • Method detection limits were established at both peaks with standards prepared using the the presence of amorphous silica. The secondary angle after 2x dilution calculation. Cristobalite’s peak same preparation process as workplace air samples. cristobalite primary peak is broad. The calculation. Possible zircon and hematite broadening tendencies can cause angle • The instruments used were Philips Cubix X-ray Diffractometer and Perkin Elmer FTIR 1600. library search finds only cristobalite, not interferences are present. The library agreement discrepancies. The library • Quality control checks redeposited from XRD silver membrane filters to IR copolymer filters opal. Particle size discrepancies in bulks search finds only cristobalite, not opal. search finds both cristobalite and opal. were evaluated for both quartz and cristobalite. can confound quantitation.

(1) XRD sample needs (2) Rinse in IPA and sonicate. (3) Filtration onto IR filter. (4) Ready to scan onto IR. confirmation by IR. XRD Scan of XRD Scan of Quartz Standard Cristobalite Standard Primary Primary peak peak The IR results were 435 μg at the primary The IR results were 280 μg at Quartz, The IR results were 622 μg at primary, peak, and 245 μg at the secondary peak Cristobalite, and amorphous silica and 737 μg at secondary, with possible after a 2x dilution calculation. Possibility of primary; and no absorbance at zircon and hematite interferences, after amorphous silica interference at the Cristobalite secondary. IR pattern 4x dilution calculation. IR pattern primary peak. IR pattern confirms confirms opal for Sample 2. confirms cristobalite for Sample 3. cristobalite for Sample 1. IR Scan of IR Scan of Quartz Standard Cristobalite Standard Summary and Conclusions References (1) NIOSH MAM, 4th ed., Method 7500 Silica, Crystalline by XRD Primary and • Some interfering minerals, such as aluminum silicates, obscure crystalline silica peaks on (filter redeposition), NIOSH 2003. (2) NIOSH MAM, 4th ed., Primary doublet Method 7603, Quartz in Coal Mine Dust by IR (redeposition), secondary peaks peak the IR, making confirmation difficult. NIOSH 2003. (3) NIOSH MAM, 4th ed., Chapter R, NIOSH 2003. (4) OSHA ID-142, Quartz and Cristobalite in Workplace • More study is needed on cristobalite’s peak broadening and peak shift tendencies. Atmospheres, OSHA 1996. • More study is needed on the different types of opal. The availability of a standard Acknowledgements reference material would be helpful. Lisa Cole, Florida Institute of Technology; Laura Moran, Galson Laboratories; Tali Baxter, Galson Laboratories