Chromatography Forum

Got a wacky idea that maybe I could do LCMS method development with various ph buffers with a MUX. Am considering modifiers such as TFA (0.1%), NH4OAc (10mm) and NH4OH (0.1%) as separate streams to the MUX. Any chance that I'll not form salt deposits on the ESI probe (Waters ZQ) and that various volitile ph modifiers could coexist, at least momentarily?

Hi Arthur,

I like your idea. I don't think you would have problems with the volatility of your buffers as each one will be introduced one after another. Maybe eventually if you do it for several days without cleaning it but for method development should be OK (assuming no more than 3 days of continuous operation) and cleaning in between with high water/low MeOH. The problem that you might have, might be with your electrospray stability as the mobile phase composition will change so rapidly, but this is something you have to try out to see how it works. I would suggest (assuming that you have a 4 way MUX) to have two neutral and one basic and acidic so you will never switch from acidic to basic or basic to acidic too fast. Alternatively, you can use the 4th way with something like high water/ low methanol (i.e. 30% methanol) to clean your system from any non-volatile deposits you may experience and avoid fast changes from acidic to basic pH and vis versa. This way, the system could take long time before needed any cleaning...

I like the idea as well. I would not worry about the Z-spray. I have used the Z-spray for weeks with ammonium phosphate. Yes, I did get the stuff to build up on the interface, but it did not bother the MS.