By Anonymous on Monday, September 10, 2001 - 04:12 am:
Hello Everybody,
When running an impurity profile for a compound, are there any specific concentration limits? When I use different concentrations, the % area purity numbers are changed dramatically.
Are there any guidelines? Thanks
By Memerick on Monday, September 10, 2001 - 09:55 am:
The question to ask is how much do you wish to see of the impurities? 0.1, 0.01, 0.001, or 0.0001%? Internally you may have a great desire to see the smallest percent, modify the method to that desire. But if USP says you must only report imputies of 0.1% or greater, you might as well aim around that.
If the impurities are unknown than the assumption can be made that the response of the impurities are simiular to that of the analyt. Make a dilution of your analyt at 0.1% of the standard concentration used in the method and inject it. If the signal is more than ten times the baseline noise (Limit of Quantitation) then the method is adequate for related substances.
The calculations for the impurities should be calculated off a low concentration of the analyt (ie. 1.0%.
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