Multiangle near infrared spectroscopy associated with common components and specific weights analysis for in line monitoring

Near infrared spectroscopy offers a number of important advantages for process monitoring. In addition to its numerous practical advantages, an important reason to use near infrared spectroscopy for process monitoring is its ability to supply versatile and multivariate information. However, in heterogeneous samples the interaction of light is complex and includes transmission, absorption, and scattering simultaneously which all affect spectra. The measurement of the signal at one point may be insufficient. A solution is to measure the medium at several points and to use specific multivariate analysis. In our study we propose to associate multipoint measurements with a common components and specific weight analysis. We monitored two media online by angular multipoint near infrared spectroscopy. For the first medium, in which only the scattering varies over time, the precipitation of silica was chosen to illustrate such a medium. For the second medium, both scattering and absorption vary, whereby microemulsions implemented for enhanced oil recovery illustrate this medium. The results showed, by combining multiangle measurements to common components and specific weight analysis, the interest of measuring at different angles. In the first case, two scattering regimes have been identified and it was possible to access the anisotropy coefficient during the silica precipitation reaction. In the second case study, on microemulsions, it was possible to identify the different phases and to separate the phenomena related to absorption and those related to diffusion. These encouraging results validate the interest of coupling multiangle measurements with multivariate multiblock analysis tools.