Thin Layer Chromatography - Purity Measurements of Phthaloyl-Amiodipine Using Over Pressurized Thin Layer Chromatography 2


Courtesy of J. Planar Chromatogr [ref. 7]


Figure 32. Comparative Scanned Chromatograms Demonstrating the Improved Performance of Over Pressurized Chromatography Relative to Normal Thin Layer Chromatography

The conventional thin layer separation was carried out on silica plates (Merk 5554) and a mixture of n-hexane:butyl acetate:ethyl acetate:chloroform (30:15:15:20) was used as the mobile phase. A normal chamber was employed with a saturation time of 30 min and a development distance of 15 cm. The plate was scanned in a similar manner to those obtained by normal thin layer chromatography. An example of some of the results obtained is shown in figure 32. The advantages of the pressurized system are clearly demonstrated; the impurity is half masked by a major peak in the chromatogram obtained by normal thin layer chromatography. Out of seven replicates, the mean level of the impurity was determined as 0.847% and 1.111% by the pressurized and normal thin layer chromatographic procedures respectively. The precision, however, as measured by the coefficient of variation was 2.9% and 6.1% respectively. It is clear that the two methods differ both in accuracy and precision but the pressurized system provides the best precision.