Near infrared spectroscopy, cluster and multivariate analysis - Characterisation of silica materials for liquid chromatography

Near infrared (NIR) reflectance spectroscopy is a well established method within the analytical chemistry and a wide range of applications, for example in the field of food and pharmaceutical products, is covered. In the era of material science and nano technology, we brought together, in this feasibility study, silica chemistry with NIR. NIR, in the fibre-optics mode, is used for morphological studies. It enables differentiation between silica materials in a three-dimensional factor-plot depending on their functionalisation and physical properties such as particle diameter and pore diameter with Q-values of 0.95 and 0.99. The well established, common reference methods for the determination of surface area and porosity are the so called Brunnauer Emmett Teller method and size-exclusion chromatography. Both methods are time-consuming and require a lot of experience. The recently elaborated NIR method offers a physicochemical quantitative description at the nano-scale level of particle size, specific surface area, pore diameter, pore porosity, pore volume and total porosity with high linearity of R 2 >0.97 for calibration and r 2 > 0.98 for validation and a bias of <2.48 × 10 -14 . Compared to the reference method, which enables the determination of the individual parameters with a relative standard deviation between 6 and 28%, the NIR method shows RSD% between only 0.010 and 13.7%, which means a fundamental improvevement in precision. The measurement takes only a few seconds so high sample throughput is guaranteed. The suitability of the newly established method in material science is demonstrated, as an example, on the silica stationary phases for liquid chromatography.