Purity methods vs Content methods [August 25, 2004]
Posted: Sun Aug 29, 2004 8:45 pm
By Richard on Wednesday, August 25, 2004 - 04:13 pm:
Question: In the pharmaceutical industry, both purity and content testing must be run on stability so, when we develop these methods, they must be stability indicating in both cases. It seems to me, therefore, that it would make sense to use the same chromatography for both methods (same column, mobile phase, gradient, etc) since we are trying to accomplish the same goal, i.e. separate the main peak from its degradation products .
Of course the quantitation would be different (and for purity you would not run a standard) but there is no reason why chromatography that has already been developed for one method, cannot be used for the other.
But in my experience, the content and purity methods are usually different. I wonder why?
Anyone see a flaw in my logic?
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By nome on Wednesday, August 25, 2004 - 11:26 pm:
purity method is accurate only when the response for all peaks is same or similar, which is not the case always.
Content methods or methods where standards (or a single standard with response factor) are used are more accurate.
There is nothing wrong in using same method for both applications.
But,for impurities(process or degradation) that have spectra and/or response very different from the main analyte or the detection level required is very low, only a content method would suffice.
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By RKK on Thursday, August 26, 2004 - 07:29 pm:
Richard: I think your statement is correct. But it's not unusual to find people doing things in a way that is more complicated than necessary. Another example is that people have a tendency to use HPLC for everything. But in cases where a stability indicating method is not neccessary HPLC would often not be necessary. So for things like dissolution and excipient content testing, a simple UV method would be sufficient in most cases.
Question: In the pharmaceutical industry, both purity and content testing must be run on stability so, when we develop these methods, they must be stability indicating in both cases. It seems to me, therefore, that it would make sense to use the same chromatography for both methods (same column, mobile phase, gradient, etc) since we are trying to accomplish the same goal, i.e. separate the main peak from its degradation products .
Of course the quantitation would be different (and for purity you would not run a standard) but there is no reason why chromatography that has already been developed for one method, cannot be used for the other.
But in my experience, the content and purity methods are usually different. I wonder why?
Anyone see a flaw in my logic?
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By nome on Wednesday, August 25, 2004 - 11:26 pm:
purity method is accurate only when the response for all peaks is same or similar, which is not the case always.
Content methods or methods where standards (or a single standard with response factor) are used are more accurate.
There is nothing wrong in using same method for both applications.
But,for impurities(process or degradation) that have spectra and/or response very different from the main analyte or the detection level required is very low, only a content method would suffice.
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By RKK on Thursday, August 26, 2004 - 07:29 pm:
Richard: I think your statement is correct. But it's not unusual to find people doing things in a way that is more complicated than necessary. Another example is that people have a tendency to use HPLC for everything. But in cases where a stability indicating method is not neccessary HPLC would often not be necessary. So for things like dissolution and excipient content testing, a simple UV method would be sufficient in most cases.