RRT calculation

[brbabu_1979]

Hi every one,
What is the limit % of RRT can we consider as an impurity while taking into calculation based on RT's.
Ex. Main peak RT is about 7.46 min, RRT for the impurity is 1.67. In sample RT of peak observed peak is 12.61 min. If I calculate the RRT, is 1.69. Could I consider the peak as my impurity peak. What could be the allowable % of RRT. Please help me. Is there any reference for this, if it is please give . Thank you very much for you help in advance.

Regards
Babu

[tom jupille]

Could I consider the peak as my impurity peak.

I don't understand the question. It's not the API, and presumably it's not an excipient, so by definition it *is* an impurity peak.

What could be the allowable % of RRT.

There is no single answer to that. Depends on how many peaks you have, how wide the peaks are, how robust is the method, and what you know (or suspect) about the chemistry of the main compound and what types of impurities are likely to be present. Ultimately the test is to run a known sample repeatedly enough times to estimate the variability (standard deviation) of the RRT.