Evaluation of Diffuse Reflection Infrared Spectrometry for End-of-Shift Measurement of α-quartz in Coal Dust Samples

Abstract

The inhalation of toxic substances is a major threat to the health of miners, and dust containing respirable crystalline silica (α-quartz) is of particular concern, due to the recent rise in cases of coal workers’ pneumoconiosis and silicosis in some U.S. mining regions. Currently, there is no field-portable instrument that can measure airborne α-quartz and give miners timely feedback on their exposure. The U.S. National Institute for Occupational Safety and Health (NIOSH) is therefore conducting studies to investigate technologies capable of end-of-shift or real-time measurement of airborne quartz. The present study focuses on the potential application of Fourier transform infrared (FT-IR) spectrometry conducted in the diffuse reflection (DR) mode as a technique for measuring α-quartz in respirable mine dust. A DR accessory was used to analyze lab-generated respirable samples of Min-U-Sil 5 (which contains more than 90% α-quartz) and coal dust, at mass loadings in the ranges of 100–600 μg and 600–5300 μg, respectively. The dust samples were deposited onto three different types of filters, borosilicate fiberglass, nylon, and polyvinyl chloride (PVC). The reflectance, R, was calculated by the ratio of a blank filter and a filter with deposited mine dust. Results suggest that for coal and pure quartz dusts deposited on 37 mm PVC filters, measurements of −log R correlate linearly with known amounts of quartz on filters, with R2 values of approximately 0.99 and 0.94, respectively, for samples loaded up to ~4000 μg. Additional tests were conducted to measure quartz in coal dusts deposited onto the borosilicate fiberglass and nylon filter media used in the NIOSH-developed Personal Dust Monitor (PDM). The nylon filter was shown to be amenable to DR analysis, but quantification of quartz is more accurate when the filter is “free,” as opposed to being mounted in the PDM filter holder. The borosilicate fiberglass filters were shown to produce excessive interference, making quartz quantification impossible. It was concluded that, while the DR/FT-IR method is potentially useful for on-filter measurement of quartz in dust samples, the use of PVC filters produced the most accurate results.

Impact of muffle furnace preparation on the results of crystalline silica analysis

“…Min-U-Sil 5 has a median diameter of 1.6 mm with 96% of the particles finer than 5 mm. Min-U-Sil 5 has been used as the source materials for NIST SRM 1878 (Huggins et al, 1985), as the base material for AIHA round robin testing (Eller et al, 1999), and was recently used by NIOSH for evaluating RCS in coal mine dust (Miller et al, 2015). The PVC filters were assigned a random number for tracking purposes.…”

Direct infrared spectroscopy for the size-independent identification and quantification of respirable particles relative mass in mine dusts

“…The degree of correlation and predictivity of the presented PLS model already demonstrates that the combination of experimental design and multivariate regression is capable of both rapid identification and reliable prediction of a variety of analytes in multimineral mixtures with minimum simple sample preparation at < 30 s per measurement, which are essential features for in situ assessment of hazards and potential real-time intervention. Once a model is established, any natural sample with matching composition is readily predicted, which is a significant advancement versus current approaches focusing on the quantification of alpha quartz only [2,21,25].…”

“…Transmission IR and DRIFTS have individually been tested as a viable method for the quantification of respirable crystalline silica [25]. However, the performance of DRIFTS is highly susceptible to particle size [26,27].…”

Chemical Identification of Single Ultrafine Particles Using Surface-Enhanced Infrared Absorption

“…Exposure to crystalline silica particles in particular is known to be a health risk in many industrial environments [37,38]. Therefore, attention has been drawn to IR-spectroscopic investigation of silica ultrafine particles in recent publications [39,40].…”