Impact of resolution on NIR PLS calibration of kaolinite content in Weipa Bauxite

The impact of spectral resolution on the quantification of kaolinite in Weipa bauxite was assessed with a view to the development of a quantitative tool for routine onsite use. Spectral data (calibration set = 204 samples, prediction set = 60 samples) were acquired at five resolution settings (2, 4, 8, 16, and 32 cm-1 ) using a Bruker MPA Fourier Transform NIR (FTNIR) instrument. Visually, the increase in resolution from 32cm-1 to 8cm-1 yielded an apparent increase in spectral feature definition whilst further increase in resolution (4 or 2cm-1) gave no additional benefit. PLS models, using identical data-treatments and spectral windows, were developed for each resolution setting. Root mean squared errors of prediction (RMSEP) were not significantly different for the resolutions 2,4,8 and 16cm-1 whilst models built at the 32cm-1 had RMSEPs significantly 4-5% worse than the other resolutions. The results demonstrated that PLS calibration of kaolinite content in Weipa bauxite was nominally affected by resolution with no predictive gain demonstrated beyond 16cm-1.