By Michael on Thursday, December 11, 2003 - 09:00 am:
I am isolating impurities for characterisation using reversed phase HPLC on a regular basis. Often, resolution with the drug substance is not good (<1.2) even on analytical scale. Also, the level of impurity is most often <0.1%, and the amount of starting material is limited to one to few gramms. It takes multiple runs to isolate. I am curious, if anyone else is doing similar work. Michael Breslav
mbreslav@prdus.jnj.com
By Uwe Neue on Thursday, December 11, 2003 - 12:26 pm:
You can improve the loadability by manipulating the pH of the separation. If you convert the compound of interest into a non-ionic form, the loadability does up 20 to 100 fold. You can find information on this on the Waters webside. We submitted a publication to J. Chromatogr., which is currently in print. If you take an approach like this, you can reduce the number of runs, or run a smaller column.
If you are interested in the parent, an overload even to the point that it overlaps with another peak is usually not a problem, since the early eluting impurities change retention at high load of the parent (displacement).
If you are interested in the impurities, this approach might not be irrational either, but you may need to do secondary purifications, i.e. 2 runs.
By Michael on Friday, December 12, 2003 - 08:23 am:
Uwe, thanks, I am familiar with your approach, as well as I am accustomed to do displacement and at-column dilution. Unfortunately, in my last projects impurities are late eluting right after the drug substances, and are not stable at basic pH. That is why, I am working at acidic (TFA) conditions.
One goal of my post is to find out how often people in other pharmaceutical companies invest in isolations of impurities which present at <0.1% level ?
By Anonymous on Friday, December 12, 2003 - 11:00 am:
In two companies I worked for, unless we knew the non-isolated related impurity was much less than 1000ppm, we identified it and determined its detector response with the proposed analytical method (ie its GC-FID or LC-UV response) in comparison with the drug substance. Often the impurity was subjected to tests to determine if any possible effects to the drug substance's activity biologically.
When it comes to drugs, the government, and safety, more information is better than less.