Measuring tablet porosity using multispectral imaging system

A multispectral imaging system with computer controlled light source of 16 light emitting diodes is applied for measuring of tablet porosity. The system is based on a subspace vector model of surface reflection. The measured spectral data are compressed on the stage of measurement and used directly for the discrimination of tablets with different porosity. The experimental results demonstrate that the multispectral imaging system is a potential method for tablet porosity measurement.     

Determination of the refractive index difference caused by the birefringence of FA (II) centers in KCl:Li

Abstract

A method is described for determining the refractive index difference caused by the birefringence of oriented F_A (II) centers in KCl:Li crystals. It is shown that the portion induced by the birefringence can be separated from an absorption spectrum measured through a polarizer-analyzer system. From this portion the refractive index difference can then be calculated with ease.     

Terahertz absorption spectra of commonly used antimalarial drugs

Optical Review - Terahertz (THz) spectra from the pure forms [i.e. the active pharmaceutical ingredients (APIs)] of four commonly used antimalarial drugs are reported. The well-defined spectral...     

Kramers-Kronig analysis on the real refractive index of porous media in the terahertz spectral range

We present a terahertz time-domain experimental technique for the detection of scattering from porous media. The method for detection of the scattering enables one to make a decision when Fresnel or Kramers-Kronig (K-K) analysis can be applied for a porous medium. In this study the real refractive index of a tablet is calculated using the conventional K-K dispersion relation and also using a singly subtractive K-K relation, which are applied to the extinction coefficient obtained from the Beer-Lambert law. The advantage of the K-K analysis is that one gets estimates both for absolute refractive index and also dispersion of the porous tablet, whereas Fresnel analysis provides only the absolute value of the index.     

A light induced configurational change of FA centres in Li doped KCl-KBr crystals

Abstract

Spectroscopic properties of F_A centres in Li doped KCl-KBr mixed crystals were studied. At low temperature light induced spectral shifts, for the F_A1 hand towards lower energy and for the F_A2 band towards higher energy, were observed. The shifts are proposed to be due to a configurational change where the electron occupied vacancy finds a new location in relation to the neighbouring chlorine and bromine ions. The recovery to the original configuration, obtained in the F → F_A conversion, is a temperature activated process.     

On the colloidal absorption bands in rubidium chloride and rubidium bromide crystals coloured with sodium

Colloidal absorption bands in rubidium chloride and rubidium bromide crystals coloured with sodium have been investigated. After a certain heat treatment of the RbCl and RbBr crystals containing F-centers, colloidal bands were observed at 585 mμ for RbCl and at 600 mμ for RbBr. The measured positions of these bands were compared with those calculated by means of the theory ofDoyle. Measurements of the areas of the absorption curves were also carried out at different temperatures.     

Refractive index changes due to F → M conversion in KBr single crystals and their applications in holography

Refractive index changes due to the F → M colour centre conversion in a KBr crystal are given as a function of angular frequency and temperature. The applicability of the results obtained for holographic recording is discussed.     

Predicting the drug concentration in starch acetate matrix tablets from ATR-FTIR spectra using multi-way methods

The amounts of drug and excipient were predicted from ATR-FTIR spectra using two multi-way modelling techniques, parallel factor analysis (PARAFAC) and multi-linear partial least squares (N-PLS). Data matrices consisted of dissolved and undissolved parallel samples having different drug content and spectra, which were collected at axially cut surface of the flat-faced matrix tablets. Spectra were recorded comprehensively at different points on the axially cut surface of the tablet. The sample drug concentrations varied between 2 and 16% v/v. The multi-way methods together with ATR-FTIR spectra seemed to represent an applicable method for the determination of drug and excipient distribution in a tablet during the release process. The N-PLS calibration method was more robust for accurate quantification of the amount of components in the sample whereas the PARAFAC model provided approximate relative amounts of components.