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Posted: Thu Oct 15, 2009 1:28 pm
by danko
From a stability point, pH of 3-5 is usually best but sometimes to low to obtain solubility, consequently a higher pH is used when dissolving.
So, in this particular case, one doesn’t expect the compound to be soluble in the mobile phase?
Any particular reason for mobile phase pH 3.5 then?
Best Regards
Posted: Thu Oct 15, 2009 3:06 pm
by Peter Apps
The reason that I asked about injection solvent was that the description of the chromatogram with a broad peak followed by a sharp one sounded like a solvent - mobile phase mismatch, while there is a big difference in pH the 20 ul volume should be small enough to avoid problems, but then again maybe it's not. There may be some other issues as well.
Can we see a chromatogram - posting instructions are in a sticky at the top of the LC page.
Peter
Posted: Thu Oct 15, 2009 3:30 pm
by HW Mueller
Do bosses and regulators linger around labs these days at midnight , etc.? There is absolutely no way to try something outside the regulatios? Seamoro, did you just vary the pH by this +/- 0.2 units? What if the original "formulator" was off by much more than this range, or you, Seamoro, how did you determine pH?
What excuse is it to use a pH incompatibility, just because solvation is slow?
Posted: Fri Oct 16, 2009 11:16 am
by seamoro
I cant post a chomatgram cause the PC hooked up with the HPLC has no USP port...lol....how bad is that!!
In reply to some of the recent posts...have you guys not read some the recent posts!!...about its solubility and its degradation!?! thats why there is two pH used.
The column is not being overloaded...(broad small peak followed by sharp good shape peak). Its a broad small peak because its barley above baseline...but after some time in solution it develops into a peak like the other (good shape)......because the peak degrades into the other isomer...
Why cant we just change the pH by more than .2 units?...because the EP has strict guidelines and how much you can tamper with a method. Go out side this and its a new method....which i may end up doing!
Posted: Fri Oct 16, 2009 11:31 am
by grzesiek
"no USP port...lol....how bad is that!! " - fortunatelly, how bad would it be if USP was watching you
"which i may end up doing!" - everybody here would be pleased
Posted: Mon Oct 19, 2009 2:35 pm
by Peter Apps
"I cant post a chomatgram cause the PC hooked up with the HPLC has no USP port...lol....how bad is that!! "
Not all that bad if it has a stiffy drive.
This is the kind of thread that makes me thankful I don't work with a bunch of regulatory acronyms measuring my pulse rate and skin conductance.
Peter
Posted: Tue Oct 20, 2009 9:25 am
by seamoro
Just wondering if my Method is in the EP ...what parameters do i need to validate for?....System Suit...Specficity..Method Precision...Stability in Solution??? Im validating for Related Substances and Assay.