@x.h.yao Thanks for participating. A lot of discussions on whether a limit or specification should be establish for not just excipient but for any nitrite contributor. It is extremely hard to define specifications since the risk of Nitrosamines is very process specific. In one instance a limit will represent a risk for a particular formulation but in some other formulation that defined limit will not represent a risk. The limit and what level should be controlled are defined in the risk assessment.
Please refer to this post that illustrates how nitrite content is used to calculate those risks.
-Naiffer