dear Lucia,
although I trust that I would follow @chrischar approach too, on the other hand, @Yosukemino recently published an interesting paper included theoretical justification and detailed calculations, especially in case you have actual levels for nitrosamines or nitrites in your excipient. perhaps it would be helpful for your case Risk Assessment and Management Strategy of Two New Nitrosamine Drug Substance Related Impurities (NDSRIs) in a Pharmaceutical Drug Product for the Treatment of a Rare Disease- from Prediction to Control-Pub - Risk Assessment Strategy / Tools & Technology - Nitrosamines Exchange
BR