Effect of process parameters on the characteristics of porous calcium phosphate ceramics for bone tissue scaffolds.

Porous hydroxyapatite (HA) has already been widely used as a bone substitute due to its similarity with the mineral part of the bone. In this work, cylindrical tablets with micro and macro porosity were produced from stoichiometric and deficient hydroxyapatites by using naphthalene as porosifier agent. The influence of the processing parameters such as Ca/P ratio of start material, calcination temperature, and naphthalene content on the characteristics of porous calcium phosphate tablets was evaluated. Three mineral phases-HA, alpha-TCP (alpha tri-calcium phosphate), and beta-TCP (beta tricalcium phos-phate)-with variable contents were identified by x-ray diffraction (XRD) and Fourier-transformed infrared spectroscopy (FT-IR). Image analysis and density measurements were used to characterize sample porosity. As expected, the total porosity of the calcinated material is not dependent on the stoichiometry of the precursor hydroxyapatite. For calcium-deficient hydroxyapatite, the increase in naphthalene content contributes to stabilize alpha-TCP phase, altering the relative phases content.

The star plot: an alternative display method for multivariate data in the analysis of food and drugs.

The star plot (SP) is a method of displaying multivariate data. It can be used to display data with more than two variables. Combined with principal component analysis (PCA), more than two PCs can be displayed in one plane. Different variants of this method are applied to an atomic absorption spectrometry (AAS) data set and to three near infra-red (NIR) spectral data sets. The results show that SP offers an easy way of visualising the multivariate data for food and drugs in a plane, and it is able to help the analyst to identify and to detect different qualities of food and drug composition. Moreover, when an object is added or removed, the PC's must be computed all over again, which is not the case for the SP-plot. The application of SP to the examples presented in the text suggests that the SP approach can be applied as an alternative method for displaying multivariate chemometric data in place of PCA or, to improve visualisation of the results already obtained with PCA.

Optimisation of the reversed phase liquid chromatographic separation of atovaquone, proguanil and related substances.

The optimisation of the separation of the antimalarial drugs, proguanil and atovaquone and six related compounds was obtained by two independent optimisation steps; the optimisation of the mobile phase composition and the optimisation of the pH. This was done using window selection diagrams (WSD) and a mixture design. The optimal conditions allow the identification of the six related compounds down to 0.1%.

Selectivity optimization for the separation of chlorophenols in an irregularly shaped experimental region in capillary electrophoresis.

The separation of seventeen chlorophenol congeners and phenol was studied as a function of several variables. The pH and the concentration of sodium dodecylsulphate (SDS) were found to be important. During the implementation of a central composite design for the optimization of the separation it appeared that a part of the domain was not feasible as it resulted in very long migration times and extremely deformed peaks. Therefore, a D-optimal design was selected within the boundaries of the feasible region. The optimization of the selectivity did not result in selective regions for a simultaneous separation. It was, however, possible to find a region for the simultaneous separation of 15 compounds. Further optimization at these optimal conditions resulted in a separation where 17 peaks could be observed.