Here is our previous discussion(link).
A manufacturer of a low-nitrite grade excipient told me that their manufacturing process inherently produces very low nitrite levels. They said it was difficult to carry out further investigations because they were unable to increase the nitrite level, even after changing the processing conditions. I suspect that the best approach to reducing nitrite levels depends on the excipient.
It would be interesting to know whether excipient manufacturers are actually using scrubbers to produce low-nitrite grades.