Broadband Photon Time-of-Flight Spectroscopy on Pharmaceutical Tablets and Dairy Products

Abstract: In this thesis, Photon Time-of-Flight Spectroscopy (PTOFS) is presented as a method to measure absorption and scattering spectra of turbid media samples in the near infra red wavelength range. In particular, absorption and scattering spectra measured on pharmaceutical tablets and dairy products are used to analyse the composition of the samples. In PTOFS, a temporally short pulse of a specific wavelength is sent through the sample. In the sample photons of the pulse are scattered and absorbed and thus the temporal shape of the pulse changes. This changed pulse shape is recorded in high temporal resolution and a model of light propagation in turbid media is fitted to the pulse shape and returns the absorption and reduced scattering coeficient. This is repeated for all wavelengths of interest in order to create a spectrum. During the work on this thesis project, the experimental setup has been improved by completing an automated measurement software. A new and more powerful super continuum light source and a new spectral filter with superior spectral resolution have been implemented. It is shown, that the new experimental setup is beneficial for the quality of the measured data. For the study on pharmaceutical tablets, the newly measured data of 70 tablets is compared to measurements on the same tablets with an older version of this setup and to data taken with Transmission Near Infra Red Spectroscopy. The results show, that the new data has less coupling between absorption and scattering. With these data it is therefore possible to create a more robust and precise compositional analysis with chemometric techniques. The measured spectra of dairy products and dilutions of cream allow an approximate fat content prediction by a fit of the absorption spectra as a linear combination of the ingredients. It is also shown, that the fat content is related to the concentration of scatterers that has been retrieved from a fit as a power law of the scattering spectra. These fits also provide information about the particle size of the scatterers in the dairy products.