How Serious is the mistake in the reporting of known
impurity to an unknown impurity.
To elaborate, the HPLC analysis of a sample for
related subsatances gave the follwing values.
Known impurity :0.84%
Total Unknown impurity : 0.14%
But the final report was reported to contain no known impurity and 0.98 % unknown impurity.

2.Will the thermally degraded impurity come under the
category of "known impurity".
I am adding the following cases too for the doubt I have.
1.RT of the thermally degraded impurity matches exactly with that present in the sample.
2. sample was injected without any thermal
degradation.

In regards to the reporting. You have to report what you actually have. A discrepancy like that would bring in a lot of questions by the FDA inspector if he saw that. You can call an impurity a known one as soon as you can identify what it is. If all you know at this point is that it is a thermal degradtion than label it as such until it is better identified.

THIS IS A VERY INTERESTING THREAD. KEEP IN MIND THE FOLLOWING THOUGHTS:

Don't lie to the FDA.

If you don't know the molecular structure you are not compelled to call it a "known" impurity.

It is not unreasonable to believe that the heat degradation peak is coeluting with the known.

If the known is only a synthetic impurity you better go back to the drawing board because your method is not specific for the most important class of degradant.