Thin Layer Chromatography - Purity Measurements of Phthaloyl-Amiodipine Using Over Pressurized Thin Layer Chromatography 1


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


Pressurized thin layer chromatography is a modification of the technique whereby a plastic membrane is placed over the thin layer plate and is held there by hydraulic pressure applied to the opposite side of the membrane. By applying the necessary pressure to the edge of the plate, the mobile phase can be forced, in a lamina flow profile, through the adsorbent layer (the stationary phase) between the plate and the membrane. In reality, this procedure really constitutes normal liquid chromatography carried out in a column having a very thin rectangular cross section. The advantages of this procedure over the normal thin layer method appear to be improved resolution and shorter analysis time. The advantages of pressurized thin layer chromatography over a similar liquid chromatography system using conventional cylindrical columns, however, is not at all clear.


Phthaloyl-amiodipine (3-(ethoxycarbonyl)-2-[(2-phthalimidoethoxy)-methyl]-4-(2-chloro phenyl)-6-methyl-5-(methoxycarbonyl)-1, 4-dihy-dropyridine) is the final intermediate in the synthesis of amiodipine benzylate a highly important anti-ischemic and antihypertensive drug. The purity of the phthaloyl-amiodipine has a significant effect on the final product. Szikszay et al. (18) used both thin layer and pressurized thin layer chromatography to analyze phthaloylamidipine for impurities to assess the relative value of each technique with regard to accuracy and precision. Separation by pressurized thin layer chromatography was carried out on fine particle silica gel plates (Merk 5548) and a mixture of n-hexane:butyl acetate:ethyl acetate:chloroform (60:15:15:20) was used as the mobile phase. An external pressure of 5 MPa was applied using 8.5 ml of mobile phase equivalent to a migration distance of 36 cm. The plate was scanned at 233 nm using a TLC Scanner 3 (Camag) in reflectance mode.