A Rotational-Linear Sample Probing Device To Improve The Performance Of Compact Near-Infrared Spectrophotometers

A novel device to probe solid ground samples by simultaneous rotational and linear displacement of their container is described and evaluated. The device improves the representativeness of spectra obtained from laboratory samples measured by near-infrared (NIR) spectroscopy using low-cost, compact instruments. These instruments typically illuminate and probe a small portion of the laboratory sample, affecting the quantitative and qualitative analytical results due to a lack of sample representativeness of the NIR spectrum. The device maximizes the sample amount assessed during the measurement, providing a more representative average spectrum. Principal component analysis of the spectral data was employed to evaluate and guide the minimization of the effect of sample heterogeneity on the analytical results. A significant improvement in the range 70 to 300% in the quantitative multivariate regression results over less representative measurement modes was obtained by employing the new device and the rotational-linear mode.