Buffers in Gradient Mobile Phase

[wanda50]

Some of our methods have a pH'ed buffer/organic in A Phase, but organic/water not pH'ed for B phase. My contention that we have a RP separation with pH effects, creating an potentially unpredictable separation. Others, such as the developers, obviously don't see this as a potential problem. I have searched for an LC/GC reference, but can't seem to locate one discussing this phenomenon. Can someone help?

thanks.

[tom jupille]

Search the Forum for posts from Bill Tindall, and also check out a series of three articles that Bill wrote in LC-GC Magazine (Nov. & Dec. 2002 and Jan. 2003; you can get them via the link to LC-GC in the "Sponsored by" area on the upper right).

The bottom line is that yes, the effective pH will shift as a function of % organic, but so long as it always shifts in the same manner, there should not be a problem, especially if you try to work at pH values reasonably far removed from your analyte pKa's.

[wanda50]

Thanks for your reply.

I see your point that as long as the pH gradient shift is consistent across an analysis, it doesn't matter. I guess I am more of simplistic separation type of person, so that I can troubleshoot a problematic method. The methods we develop are for a quality lab which just runs as written without thinking about what is going on. I've had to troubleshoot some of those methods, and I just get annoyed with ion pairing and pH "gradient" methods, especially when the 2 are combined. So, enough complaining from me.

thanks again.