title: Stability-indicating colorimetric assay for indicine N-oxide using TLC.
abstract: Aliquots of aqueous solutions in which indicine N-oxide may be degraded were mixed with 0.5 M formic acid (1:3) to adjust the pH to approximately 2-4 to quench the reaction and to ensure adequate TLC resolution. Silica-coated aluminum sheets were used to isolate indicine N-oxide by cutting the appropriate region from the chromatogram. By a modification of a known procedure, the silica gel then was treated with an acetic anhydride-diglyme mixture, and the mixture was heated to convert the drug to a pyrrole, which was then coupled with 4-dimethylaminobenzaldehyde to produce a color. The absorbance of the resulting solution was determined at 566 nm, and the apparent molar absorptivity, epsilon, based on the final indicine N-oxide concentration was 6.13 x 10(4). The recovery was approximately 92%, and the assays were readily reproducible with a coefficient of variation of 4.4%.
mesh_terms: D002855:Chromatography, Thin Layer / Q000379:methods*; D003124:Colorimetry / Q000379:methods*; D003497:Cyclic N-Oxides / Q000032:analysis* / Q000592:standards; D004355:Drug Stability; D007700:Kinetics; D011763:Pyrrolizidine Alkaloids / Q000032:analysis* / Q000592:standards
chemical_list: D003497:Cyclic N-Oxides; D011763:Pyrrolizidine Alkaloids; C013095:indicine-N-oxide