Chromatography Forum

Can someone please explain the use of application of a sawtooth gradient? Is it applicable in a binary pump system in RP LC?

I see that folks are reading this...does anyone have any input? Is a sawtooth gradient relevant in a binary pump system? Don't I need at least two solvent systems to vary ionic strength? And if my analytes are neutral, not ionic...is it still relevant?

I know I'm reading this thread to see what others can contribute. I haven't used a sawtooth gradient before but I'm interested in seeing what experience others may have. A quick Google search brought up a few hits where a sawtooth gradient was applied to proteins and peptides. The methods used were all RP-LC. If you're using a binary pump, you can run a sawtooth gradient it would seem. Will it help your separation more than a linear gradient or a step gradient? Only the data will answer that question.

The relevance of it is this:

If you wish to elute a peak, and then you want a pause while nothing else elutes, perhaps because you are doing two-dimensional liquid chromatography (which I never have; I'm not mad), or because you have some sort of online detector that needs more time to look at the peak before the next peak elutes, you need to do something to stop subsequent peaks eluting.

If you are running a gradient method, and the peak comes out at 50%, if you just put a plateau in the gradient at, say, 52%, it won't actually stop the next peak from eluting. It just means the next peak will move in an isocratic way along the column, and it will get broader as it does so.

Some people have published papers where instead of holding at 52% (these are random example %'s, not taken from any paper), you wait until just after the 50% peak has eluted, and then drop the percentage back to 40%, so that in theory nothing on the column is moving at all. This should maintain the peaks as tight, non-diffusing bands, which can then be moved on again when you're ready, by increasing the mobile phase back to above 50%.

And to answer the rest of your question, yes, you need a system capable of varying the solvent mix (but you would have to have one for this sort of work anyway, because you're running a gradient). It could be done on any system capable of pumping a gradient. It could be done in various modes of chromatography, including reverse phase (with neutral or charged compounds) as well as, I presume, ion chromatography (about which I know very little).