Interpretation of electron diffraction data from organic microcrystals: a theoretical perspective.
The current framework for the quantitative analysis of transmission electron diffraction data from organic microcrystals is discussed. The appropriate formulation depends upon the crystal perfection: solution-grown material tends to be nearly perfect with regular elastic bends whilst the epitaxial samples are usually considerably less perfect with highly irregular bends. It is possible to obtain Bragg intensity data which are near-kinematical and thus amenable to ab initio structure analysis. Thereafter, the further refinement of the model proceeds with a consideration of dynamical and crystal bending effects. If both of these are small it is a good approximation to analyse them independently rather than use the correct description of dynamical scattering from a deformed foil. The analysis of three-dimensional data sets from tilt series is considered. Although the technique has been successfully demonstrated in several instances there are still details of the analysis that need further clarification.
Kink defects in linear chain molecules-structure analysis based on spot and continuous diffuse electron diffraction intensities
Abstract Calculated defect diffuse scattering patterns, using the kink defect model employed earlier to explain changes in Bragg electron diffraction intensities for heated n-paraffins, are shown to account best for observed diffuse data from solution-grown and epitaxially grown micro-crystals. The presence of significant diffuse scattering below 15°K, moreover, indicates that such chain kinks are stable in the crystal lattice.
HPLC determination of chlorhexidine gluconate and p-chloroaniline in topical ointment.
A novel fast isocratic reversed-phase HPLC method for simultaneous determination of chlorhexidine and its degradation product p-chloroaniline was developed. Zorbax SB Phenyl column (75 mm x 4.6 mm, 3.5 microm) was used for the separation. Mobile phase composed of acetonitrile and buffer solution of 0.08 M sodium phosphate monobasic containing 5 ml of triethylamine (0.5%) and adjust with 85% phosphoric acid to pH 3.0 in ratio 35:65 (v/v) pumped isocratically at flow rate 0.6 ml min(-1) was used. UV detection was performed at 239 nm, the total analysis time was about 10 min. The method is suitable for practical routine analysis of topical ointment in the quality control laboratory.