engleski

Determination of the thiamazole related substances in pharmaceutical formulations by HPLC-UV method

A novel high-performance liquid chromatography method with UV detection was proposed for determination of the thiamazole related substances in pharmaceutical formulation. Thiamazole is an active substance used in drug products for the treatment of hyperthyroidism. It is a thyreostatic that inhibits the synthesis of natural thyroid hormones T3 and T4 by inhibiting the incorporation of iodine. There are no official pharmacopoeial methods for determination of the thiamazole related substances in drug products, and HPLC method was rarely used for this purpose. The spectrum of thiamazole molecule shows intensive band at ~250 nm due to the internal transitions within the coordinated ligand. Therefore, we developed and validated a new HPLC method with UV detection for determination of the thiamazole related substances. The external standard calibration was used and the method was validated according to the ICH guidelines. A gradient mixture of the mobile phase consisted of 0.03 M ammonium acetate buffer and acetonitrile. Chromatography was performed at the steady flow rate of 0.7 ml/min through a Zorbax SB-C18 column at 25°C, while the variable UV detector set at 252 nm was used. The method was tested for specificity, linearity, quantitation limit (LOQ), detection limit (LOD), accuracy, precision and robustness. We have found eight unknown impurities and thiamazole related substance C in the control sample. Forced degradation study showed that the thiamazole was susceptible to the degradation when exposed to increased temperature and prolonged UV radiation, while it was more resilient to degradation in acid, alkaline and oxidative environments. Impurity C is the main product of the acid hydrolysis and can be considered a degradation product. Oxidation also lead to the formation of eight unknown impurities previously not detected in control samples. The method was accurate and linear in a range 0.5 μg/ml - 10.1 μg/ml for impurity C, while the recovery was from 95.16 to 102.37%. Detection and quantitation limits were measured to be 0.17 μg/ml and 0.5 μg/ml, respectively. The proposed method proved to be precise, robust and specific, with no interference from excipients. The new HPLC method has been proved to be far superior to the TLC method, a less expensive LC method commonly used in the past by pharmaceutical laboratories. We used a mixture of toluene, 2-propanol and concentrated ammonia as the mobile phase and a visual estimation of the spot intensity under the UV light at 254 nm. The validated TLC method showed much lower detection and quantitation limits of 1 μg/ml and 2 μg/ml respectively, when compared to HPLC method. Similarly, the TLC method was linear only in the range between 5 and 25 μg/ml for impurity C. We can conclude that the newly proposed HPLC method is highly reliable, sensitive, accurate, precise, robust, effective and moderately fast to be used for determination of the thiamazole related substances in pharmaceutical products.

thiamazole ; related substances ; HPLC ; UV method

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