Abstract

Time-resolved spectroscopy in the visible and near-infrared (NIR) regions was used in a feasibility study for analysis of solid pharmaceuticals. The objective of the experiments was to study the interaction of light with pharmaceutical solids and to investigate the usefulness of the method as an analytical tool for spectroscopic analysis. In these experiments, a pulsed Ti:sapphire laser and white light generation in water was utilized to form a pulsed light source in the visible/NIR region. The light was focused onto the surface of tablets, and the transmitted light was detected by a time-resolving streak camera. Two types of measurements were performed. First, a spectrometer was put in front of the streak camera for spectral resolution. Secondly, the signal originating from different locations of the sample was collected. Time-resolved and wavelength/spatially resolved data were generated and compared for a number of different samples. The most striking result from the experiments is that the typical optical path length through a 3.5-mm-thick tablet is about 20-25 cm. This indicates very strong multiple scattering in these samples. Monte Carlo simulations and comparison with experimental data support very high scattering coefficients on the order of 500 cm^-1. Furthermore, the data evaluation shows that photons with a particular propagation time through the sample contain a higher chemical contrast than other propagation times or than steady-state information. In conclusion, time-resolved NIR spectroscopy yields more information about solid pharmaceutical samples than conventional steady-state spectroscopy.

Comprehensive study of solid pharmaceutical tablets in visible, near infrared (NIR), and longwave infrared (LWIR) spectral regions using a rapid simultaneous ultraviolet/visible/NIR (UVN) + LWIR laser-induced breakdown spectroscopy linear arrays detection system and a fast acousto-optic tunable filter NIR spectrometer

Clayton S.C Yang, Feng Jin, Siva R. Swaminathan, Sita Patel, Evan D. Ramer, Sudhir B. Trivedi, Ei E. Brown, Uwe Hommerich, and Alan C. Samuels
Opt. Express 25(22) 26885-26897 (2017)

Broadband photon time-of-flight spectroscopy of pharmaceuticals and highly scattering plastics in the VIS and close NIR spectral ranges

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Time and wavelength resolved spectroscopy of turbid media using light continuum generated in a crystal fiber

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Density-dependent determination of scattering properties of pharmaceutical tablets using coherent backscattering spectroscopy

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Opt. Express 26(16) 19964-19971 (2018)

Authentication of gold nanoparticle encoded pharmaceutical tablets using polarimetric signatures

Artur Carnicer, Oriol Arteaga, Josep M. Suñé-Negre, and Bahram Javidi
Opt. Lett. 41(19) 4507-4510 (2016)