Reference Standards

Hi there,

in relation to API related Nitrosamines we were facing the issue that the provided standard from an external source seems to be of poor quality.

Does any one have good experience with a company providing API related nitrosamine standards or maybe an recommendable contract lab able to produce API related standards?

Is there any option to perform a confirmatory testing without the respective standards in place?

I would appreciate any comments/support

All the best and thank you

Can you share more on the specific API related nitrosamine you are interested in? Feel free to also share what you need with USP’s new pharmaceutical analytical impurities program which was established recently to create quality reference materials for pharmaceutical impurities. Your inputs can help shape the pipeline of new impurities materials being developed. You can email


In that particular case we were looking for standards for Imidazole based Nitrosamines.

USP Reference Standard materials in their Istore… and don’t forget to also reach out if you have specific need on Nitrosamine Impurity standards.

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If the impurity is a NDSRI and UV active, you may check the response factor against the respective API. Use impurity and API in equal concentration (say, 0.1 mg/mL) in suitable diluent and check the peaks response with LC-UV. If the impurity is pure, you would get the response factor close to ‘1’. Make sure to do the salt correction wherever applicable.

Dr. Suresh

We’ve had good luck with Toronto Research for impurities not offered by USP.

Please contact us at if drug related nitrosamine impurities are not available with USP

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