During the process development of naratriptan hydrochloride we have made an unusual observation about the enhanced levels of intermediate 3 as an impurity (impurity B) in the final stage. Detailed investigation has led to the conclusion that impurity B is not only a carried over but also formed via acid catalyzed dehydration of yet another process related impurity. The present work details a report of the journey towards the development of an efficient process for the commercial production of naratriptan hydrochloride substantially free from the impurity B.
Background: Presence of residual solvents in pharmaceuticals can be a potential risk factor to human health because of its toxicity. Gas chromatography used for its excellent separation abilities and lower limit of detection. Racecadotril, an antidiarrheal drug, reported having four residual solvents, namely n-Hexane, isopropyl alcohol, toluene and dimethylformamide. Estimation the amount of these solvents in active pharmaceutical ingredients to ensure that they are within the permissible limits as per ICH guidelines necessary.
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Objective: To develop and validate a new, simple and sensitive gas chromatographic method for simultaneous determination of n-Hexane, isopropyl alcohol, toluene and dimethylformamide in racecadotril.
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Method: The residual solvents of racecadotril estimated using a gas chromatographic method by direct injection using FID as a detector. This method employed a 30-meter long DB-FFAP nitroterephthalic-acid-modified polyethene glycol column with 0.53 mm in inner diameter and 1 μm film thickness. The separation achieved using nitrogen as the carrier gas at a flow rate of 2.8 mL/min using a split ratio of 1:10.
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Results: The peak shape for all the residual solvents from racecadotril was symmetric with excellent resolution eluting at reasonable retention time. The limit of detection of n-Hexane, isopropyl alcohol, Toluene and dimethylformamide found to be 6, 27, 14 and 42 ppm respectively. The developed method exhibited excellent linearity for each residual solvents in the range studied.
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Conclusion: The developed gas chromatographic method is simple, specific, precise, accurate and sensitive. Hence, the method can be successfully used in the pharmaceutical companies and research laboratories for simultaneous determination of residual solvents in racecadotril active pharmaceutical ingredients.
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