STUDY ON THE QUALITY OF RETINAMIDIC ACID

AIM　To determine retinamidic acid and its isomer by reversed-phase HPLC and to control the remains of reactants, tretinoin and p-aminobenzoic acid, in retinomidic acid by normal-phase HPLC. METHODS　A reversed-phase HPLC system consisting of an ODS column and a mixture of methanol - 0.02 mol.L^-1 sodium dihydrogen phosphate solution (82∶18) as the mobile phase was used. The flow rate was 1.0 mL.min^-1 and detection was effected at 367 nm. A normal-phase HPLC system including a CN column and a mixture of n-hexane-alcohol-glacial acetic acid (100∶10∶0.3) as the mobile phase was used. The flow rate was 0.8 mL.min-1 and the wavelength of detection was 320 nm. RESULTS　The assay of retinamidic acid displayed good linearity over the concentration range of 0.05～0.5 μg.μL^-1 and the limit of detection was 3 ng in the reversed-phase HPLC. The detecting limit of tretinoin was 5 ng with normal-phase HPLC. Three lots of retinamidic acid samples were analyzed with the two HPLC methods. CONCLUSION　Retinamidic acid and its isomers were separated perfectly. Tretinoin and p-aminobenzoic acid were not detected in the samples. The reversed-phase HPLC is simple, accurate and reproducible. It can be used to control the quality of retinamidic acid and its isomers. The normal-phase HPLC is better in separating tretinoin and p-aminobenzoic acid and may be used to control the impurity of reactants.