Toward rapid silica analysis of CPDM samples: A study of dust recovery and quartz estimation using lab and field samples

In US coal mines, the continuous personal dust monitor (CPDM) is frequently used to determine miners' exposure to respirable dust. Capabilities to analyze the respirable crystalline silica (RCS) content of that dust are needed, but the CPDM sample collection substrate ("stub") interferes with direct analysis. To overcome this challenge, a three-step method is proposed to recover the dust from the stub, deposit the dust on a polyvinyl chloride (PVC) filter, and analyze the recovered dust by Fourier Transform Infrared Spectroscopy (FTIR) to determine the quartz content (as a proxy for RCS). Recent work has established procedures for the latter two steps using representative dust samples suspended in isopropyl alcohol (IPA). That work is extended in the current study to also address the dust recovery step, testing both IPA and deionized water (H2O) as recovery liquids. Here, blank CPDM stubs were subjected to the entire three-step method and results were used to establish a quartz mass correction for residue that is recovered from the stub itself. Then, the method and correction were applied to lab-spiked and field CPDM stubs. For spiked samples, predicted and expected quartz mass values were highly correlated (R2 values >0.97 regardless of recovery liquid or application of the blank CPDM-stub correction); though predicted values were consistently lower than expected values (regression line slopes between 0.84 and 0.86), which might be related to effects of total recovered sample mass on the deposition pattern achieved on PVC filter. For the field samples, IPA proved to be a much more efficient recovery liquid than H2O. Unfortunately, the evaluation of the predicted quartz mass results on the field samples was confounded by apparent issues with reference filter samples intended to determine expected values.