Multicomponent Measurement of Respirable Quartz, Kaolinite and Coal Dust using Fourier Transform Infrared Spectroscopy (FTIR): A Comparison Between Partial Least Squares and Principal Component Regressions

Exposure to respirable crystalline silica (RCS) is potentially hazardous to the health of thousands of workers in Great Britain. Both X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy can be used to measure RCS to assess exposures. The current method outlined in the Health and Safety Executive’s (HSE) Methods for the Determination of Hazardous Substances (MDHS) guidance series is ‘MDHS 101 Crystalline silica in respirable airborne dust - Direct-on-filter analyses by infrared spectroscopy or x-ray’. This describes a procedure for the determination of time-weighted average concentrations of RCS either as quartz or cristobalite in airborne dust. FTIR is more commonly employed because it is less expensive, potentially portable and relatively easy to use. However, the FTIR analysis of RCS is affected by spectral interference from silicates. Chemometric techniques, known as Partial Least Squares Regression (PLSR) and Principal Component Regression (PCR), are two computational processes that have the capability to remove spectral interference from FTIR spectra and correlate spectral features with constituent concentrations. These two common chemometric processes were tested on artificial mixtures of quartz and kaolinite in coal dust using the same commercially available software package. Calibration, validation and prediction samples were prepared by collecting aerosols of these dusts onto polyvinylchloride (PVC) filters using a Safety in Mines Personal Dust Sampler (SIMPEDS) respirable cyclone. PCR and PLSR analyses were compared when processing the same spectra. Good correlations between the target values, measured using XRD, were obtained for both the PCR and PLSR models e.g. 0.98–0.99 (quartz), 0.98–0.98 (kaolinite) and 0.96–0.97 (coal). The level of agreement between PCR and PLSR was within the 95% confidence value for each analyte. Slight differences observed between predicted PCR and PLSR values were due to the number of optimal principal components applied to each chemometric process. The presence of kaolinite in these samples caused an 18% overestimation of quartz, for the FTIR, when following MDHS 101 without a chemometric method. Chemometric methods are a useful approach to obtain interference-free results for the measurement of RCS from some workplace environments and to provide a multicomponent analysis to better characterise exposures of workers.

Consonance Preferences Within an Unconventional Tuning System

Recently, Bowling, Purves, and Gill (2018a), found that individuals perceive chords with spectra resembling a harmonic series as more consonant. This is consistent with their vocal similarity hypothesis (VSH), the notion that the experience of consonance is based on an evolved preference for sounds that resemble human vocalizations. To rule out confounding between harmonicity and familiarity, we extended Bowling et al.’s (2018a) procedure to chords from the unconventional Bohlen-Pierce chromatic just (BPCJ) scale. We also assessed whether the association between harmonicity and consonance was moderated by timbre by presenting chords generated from either piano or clarinet samples. Results failed to straightforwardly replicate this association; however, evidence of a positive correlation between harmonicity and consonance did emerge across timbres following post hoc exclusion of chords containing intervals that were particularly similar to conventional equal-tempered dyads. Supplementary regression analyses using a more comprehensive measure of harmonicity confirmed its positive association with consonance ratings of BPCJ chords, yet also showed that spectral interference independently contributed to these ratings. In sum, our results are consistent with the VSH; however, they also suggest that a composite model, incorporating both harmonicity as well as spectral interference as predictors, would best account for variance in consonance judgments.