By Anonymous on Tuesday, May 4, 2004 - 01:32 pm:
How can a person just LOOK at the structural formula of a drug and say which mobile phase is adequate to use? That it's better an acid mobile than a base one or the opposite. My good! will i have to enter the university again? I haven't seen much of chemistry or at least haven't paid attention to it as i should have. Is there any book that can help? Organic chemistry? Inorganic chemistry? or books more specific? Or should i give up dealing with LC hehehe....
By Uwe Neue on Tuesday, May 4, 2004 - 04:45 pm:
I have seen experienced chromatographers do that, of course with the caveat that this is a starting point and you may need to tweak things a bit. I have never contemplated playing this game, but it is quite feasible.
By tom jupille on Tuesday, May 4, 2004 - 08:51 pm:
Generally, coming up with a *detailed* mobile phase from looking at the formula comes from previous experience with similar compounds.
That said, many general conclusions can be made from looking at the structure (e.g., you usually want to stay away from the pKa so if it's an acid, start low, if it's a base, start high).
From there, a single gradient run can tell you whether you will be able to fit your peaks in an isocratic separation or whether a gradient will be required; if the former, you can estimate a reasonable %B.
Probably the best book is Practical HPLC Method Development by Snyder, Glajch, & Kirkland. You can order it from Amazon via a click-through from the LC Resources web site (the link on the upper left of the forum here). By way of "truth in advertising", we do get a couple of bucks from Amazon if you order in this manner. :)
By Anonymous on Wednesday, May 5, 2004 - 05:25 am:
I've just ordered the book.... too expensive heheh (at least for me that earn US 600,00 a month)
U$ 13,00 just to ship.... :o)
but that's ok.... i hope this can help me dealing with this problem of mine.....
thank you so much for the tip.....
any other hint, i'll accept it
THANKSSSSSSSSSSSSSS AGAINNNNNNNNNNN!!!!
By Tom Mizukami on Wednesday, May 5, 2004 - 10:19 am:
Hi,
Take a look at NIST SRM 870 http://patapsco.nist.gov/srmcatalog/certificates/870.pdf
it has some good information regarding structure function relationships for HPLC.
Other than what Tom said above, I like to take a good look at the structure to anticipate what problems might be encountered and form a game plan if they occur. Peak shape problems need to be dealt with early in the development process.
Looking at the structure you should be able to:
identify acidic and basic groups and approx. pKa's, identify chromaphores or total absense of chromaphores, identify lone pair electrons that can form 5 or 6 member rings and thus might pose chelation issues, mentally perform the Fischer projections and determine if your compound could from structural confomers (look at moxipril or lisinopril). Each of these can cause problems with an HPLC separation and are addressed differently.
Even if I think I know a mobile phase combination that will work I still like to use a standard screening methodology using scouting gradients and DryLab. I usually have the 2 or 3 days required to look for a global maximum rather than settle for a local maximum.
Since Tom Jupille is too modest to plug his own course, I'll do it. A few days spent in one of LCResources method development courses would be time well spent. Good Luck!