10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Analysis of Crystalline Silica Aerosol Using Quantum Cascade Laser-based Infrared Spectroscopy
SHIJUN WEI, Pramod Kulkarni, Lina Zheng, Kevin Ashley, Centers for Disease Control and Prevention, NIOSH
Abstract Number: 1487 Working Group: Instrumentation
Abstract The objective of this study was to extend the application of a previously developed approach [1] involving quantum cascade laser based infrared spectroscopy (QCL-IR), to quantify airborne concentration of crystalline silica in workplace aerosols. This method involved collection of crystalline silica-containing aerosol on a mixed cellulose ester filter, followed by filter pretreatment using a low-temperature plasma asher to remove the organic components in the sample matrix. The ashed sample was then resuspended in aqueous phase, which was subsequently redeposited as a dried spot (1-3 mm diameter) on a polycarbonate (PC) filter. The dried spot was analyzed using QCL-IR to obtain IR transmission spectra [1]. A syringe filtration method, involving PC filter sandwiched by two orifice plates, was developed to allow redeposition of the ashed suspension as a small, dried deposit. The method was calibrated using aqueous suspensions of the α-quartz standard reference material (SRM 1878a). QCL-IR transmittance spectra in the range 750 -1030 cm-1(α-quartz characteristic peak at 798 cm-1) were measured and analyzed for silica content, following the approach outlined by Wei et al. [1]. A calibration model was constructed using partial least square regression to predict α-quartz mass from the QCL-IR spectra. The detection limit for α-quartz was determined to be 0.39 μg, 0.53 μg, and 1.94 μg for spot diameters of 1 mm, 1.5 mm, and 3 mm respectively. These detection limits are significantly lower than those from the current standardized X-ray diffraction (XRD) or infrared spectrometry(IR) methods. The method was extended to measurement of α-quartz concentration in workplace aerosol generated during power cutting of fiber cement and natural stone objects, and those from a coal mine dust. The measurements were compared with those from the standard XRD and FTIR methods and showed good agreement, even for samples with matrix effects and interference from kaolinite mineral. The results offer promise for further development of sensitive filter-based laboratory methods using QCL-IR spectroscopy.
References [1] Wei et al., Measurement of Crystalline Silica Aerosol Using Quantum Cascade Laser–Based Infrared Spectroscopy, Scientific Reports, 7 (1), 13860, 2017.