Abstract
Airborne respirable crystalline silica (RCS) is a hazard that can affect the health of workers, and more sensitive measurements are needed for the assessment of worker exposure. To assess the use of Raman microscopy for the analysis of RCS particulate collected on filters, aliquots of quartz or cristobalite suspended in isopropanol were pipetted onto silver filters. Samples were measured by arbitrarily selecting positions along the filter and collecting spectra at 50 discrete points. The calculated limits of quantification on test samples were between 0.066–0.161 and 0.106–0.218 μg for quartz and cristobalite, respectively. Three respirable quartz calibration dusts (A9950, NIST 1878 and Quin 1B) with different mass median aerodynamic particle sizes obtained similar Raman response relationships per unit mass. The difference between NIST 1878 and Quin 1B was not significant (p = 0.22). The intermediate measurement precision of replicate samples was 10–25% over the measured range for quartz (0.25–10 μg) and could potentially be improved. Results from mixtures of quartz and cristobalite were mostly within 10% of their theoretical values. Results from samples of 6% quartz in calcite were close to the theoretical quartz mass. The upper measurement limit for a mixture of 20% RCS in the light absorbing mineral hematite (Fe2O3) was 5 μg. These data show that Raman spectroscopy is a viable option for the quantification of the mass of respirable crystalline silica on filters with a limit of detection approaching 1/10th of that obtained with other techniques. The improvement in sensitivity may enable the measurement of particulate in samples from low concentration environments (e.g. inside a mask) or from miniature samplers operating at low flow rates. ©2017 Crown copyright. Journal of Raman Spectroscopy published by John Wiley & Sons, Ltd. © 2017 Crown copyright. Journal of Raman Spectroscopy published by John Wiley & Sons, Ltd.
Highlights
Respirable sized particles can penetrate to the alveoli of the lung.[1]Their aerodynamic size range is defined by an InternationalOrganisation for Standardisation/Centre European de Normalisation/American Congress of Government Occupational Hygienists convention[1] as those particles mostly
Precision of the measurement between days was approximately 20%. This large between day variation did not change the results for the mass of respirable crystalline silica (RCS) because the measured value is corrected for the change in intensity, which is relatively consistent during the analysis
The wileyonlinelibrary.com/journal/jrs comparison between A9950 and NIST 1878a was borderline significantly different (p = 0.04); most values were close to the NIST 1878a trend line relationship below 10 μg and if a single value at the highest loading is removed the response relationship with mass loading from the two materials is not significantly different (p = 0.08). These results demonstrate that the difference in response due to aerodynamic particle size within the respirable size range will not significantly affect the reported result for most samples within the mass range 0.25–10 μg
Summary
Respirable sized particles can penetrate to the alveoli of the lung.[1]Their aerodynamic size range is defined by an InternationalOrganisation for Standardisation/Centre European de Normalisation/American Congress of Government Occupational Hygienists convention[1] as those particles mostly
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