Centers for Disease Control and Prevention , National Institute for Occupational Safety and Health , Cincinnati , Ohio 45226 , United States.
Anal Chem. 2018 May 15;90(10):6229-6239. doi: 10.1021/acs.analchem.8b00830. Epub 2018 May 2.
A Raman spectroscopy based method has been developed for measurement of trace airborne concentrations of respirable crystalline silica (RCS) using various aerosol sampling and analysis techniques. Three aerosol microconcentration techniques were investigated for effective coupling of collected particulate samples with micro-Raman spectroscopy: (i) direct analysis on a particulate filter after focused aerosol collection using a converging nozzle; (ii) analysis of dried particulate deposit on a filter obtained directly from the aerosol phase using the Spotsampler device; and (iii) analysis of a dried spot (∼1-3 mm diameter) obtained by redepositing the particulate sample, after low-temperature plasma ashing of the filter sample. The deposition characteristics (i.e., spot diameter, shape, and deposit uniformity) of each technique were investigated. Calibration curves were constructed and detection limits were estimated for α-quartz using the A Raman Si-O-Si stretching-bending phonon mode at 465 cm. The measurement sensitivity could be substantially improved by increasing the signal integration time and by reducing the particle deposition area. Detection limits in the range of 8-55 ng could be achieved by microconcentrating the aerosol sample over a spot measuring 400-1000 μm in diameter. These detection limits were two to three orders of magnitude lower compared to those attainable using current standardized X-ray diffraction and infrared spectroscopy methods. The low detection limits suggest that near real-time measurements of RCS could be achieved with limits of quantification ranging from 2 to 18.5 μg/m (at 10 min collection time and 1.2 L/min sampling flow rate), depending on microconcentration technique used. The method was successfully extended to the measurement of α-quartz air concentration in representative workplace aerosol samples. This study demonstrates the potential of portable micro-Raman spectroscopy for near-real time measurement of trace RCS in air.
一种基于拉曼光谱的方法已经被开发出来，用于使用各种气溶胶采样和分析技术测量可吸入结晶硅（RCS）的痕量空气中浓度。研究了三种气溶胶微浓缩技术，以有效将收集的颗粒样品与微拉曼光谱结合：（i）在使用收敛喷嘴聚焦气溶胶收集后，直接在颗粒过滤器上进行分析；（ii）直接从气溶胶相使用 Spotsampler 设备分析在过滤器上获得的干燥颗粒沉积物；和（iii）通过低温等离子体灰化过滤样品后，重新沉积颗粒样品，分析干燥斑点（直径约 1-3 毫米）。研究了每种技术的沉积特性（即斑点直径、形状和沉积均匀性）。使用 A 拉曼 Si-O-Si 伸缩弯曲声子模式在 465 cm 处构建了α-石英的校准曲线，并估计了检测限。通过增加信号积分时间和减小颗粒沉积面积，可以大大提高测量灵敏度。通过将气溶胶样品浓缩在直径为 400-1000 μm 的斑点上，可以实现 8-55 ng 的检测限。与当前使用的标准 X 射线衍射和红外光谱方法相比，这些检测限低两个到三个数量级。低检测限表明，使用近实时测量技术可以实现 RCS 的近实时测量，定量限范围为 2 至 18.5 μg/m（在 10 分钟收集时间和 1.2 L/min 采样流量下），具体取决于使用的微浓缩技术。该方法成功扩展到测量代表性工作场所气溶胶样品中的α-石英空气浓度。本研究证明了便携式微拉曼光谱技术在空气中痕量 RCS 的近实时测量中的潜力。
