Interlaboratory Comparison of Spectrometric Laboratory Measurements of a Chlorite Rock Sample

Abstract

The focus of this study was the comparative analysis and evaluation of reflectance measurements (350 nm–2500 nm) of a chlorite rock sample, which were collected by 26 institutions in 42 different spectroscopic set-ups as a part of an international measurement comparison designed to document the plurality in laboratory reflectance spectroscopy. The impacts of the different set-ups on the chlorite spectra were determined by analysing the parameter variations of two characteristic chlorite absorption features at 1400 nm and 2345 nm and interpretation based on user-provided metadata. The positions of the 1400 nm absorption features showed a standard deviation of 1.4 nm. Larger deviations were observed for the shoulders, widths, depths and areas. Here, the strongest deviations could be clearly related to impacts of unfavourable background materials and unsuitable illumination types. The positions of the absorption feature at 2345 nm showed a standard deviation of 16 nm and the variations in absorption width were stronger compared to the 1400 nm feature. In contrast, the variations of depths and areas of the feature at 2345 nm were comparable to the variations we observed for the 1400 nm feature but could not be assigned to singular influencing factors. Although the majority of the spectra showed the typical shapes and specific features of chlorite, strong deviations were present in a few spectra which are likely to hamper the spectral identification of chlorite and quantitative spectral analysis. Thus, the results of this study underline the necessity to define measurement standards and protocols and to provide basic information for future standards.