Dear all,
this is kartheek reddy
what is purity and known and unknown impurity.
for example a material specification is listed below
A) material putiry NLT-99.0%
B) Known impurity A NMT 0.05%
C) Known impurity B NMT 0.80%
D) Total impurities NMT 1.0%
here my question is what is the maximum % of Total impurities.
The answer depends! It depends on your API and its expiry specification or the USP monograph. Usually as the potency of the API decreases in the drug product or substance the concentration of the related substances increase. While related substances (RS) are impurities, not all impurities are RS (think of cyanide that is added).
Thus;
Total impurity = Individual known impurity + unknown impurity
Where a known impurity has been identified by MS, NMR… Unknowns cannot be identified or several structures are possible.
In your case the API has been guaranteed to be 99.0% pure. Known impurity A is 0.05% and B 0.80%. Thus total impurities is 0.85% which is less the specification (guarantee) of 1.0%.