Does nano/micro HPLC improve MS signal for small molecules?

[ChromKing]

I have heard a lot of claims that micro and nano flow improves overall signal for small molecule drugs, but I don't see many publications about it. It seems that running nano or micro-flow improves the ionization efficiency and transfer efficiency into the MS but it comes with the drawback of decreased sample injection volume. Overall it seems a wash with the signal when all the factors are taken into account, and nano is really only useful when sample volumes are very small and there is not much to inject onto the system. If you have have had any luck improving overall sensitivity I would like to hear about it.

[lmh]

I think you're probably right, but I'd go further: nano-plumbing is such a nightmare that I wouldn't want to go that way unless I was unable to get adequate sensitivity by any other means. It probably is more sensitive, but if you have enough material to get an adequate concentration out of the end of an ESI spray needle using conventional flow LC, why endure a system where a 1uL dead volume (unnoticeable at conventional flows) completely destroys the peaks?
Protein people are unlucky. The molar concentration of proteins tends to be low, so the molar concentration of any peptide from a protein will also be low. They haven't got many molecules in their sample, so it makes sense to keep the concentration as high as possible by injecting what they have, into a very narrow column with very low flow.

[sav]

I agree with lmh. Furthermore, work with nano-LC-MS is much more tricky than with standard LC-MS systems. Furthermore, nano-ESI-MS get dirty much faster and deeper (transfer optics, quad etc.).

[ChromKing]

How do feel about microflow? The exsigent system seems pretty good on paper, and the dead volume seems to be a small issue. It looks like pretty similar gradient times can be achieved relative to traditional flow if you use the in source columns that a few vendors are making for sciex instruments. There was a paper showing methotrexate improved 10x in sensitivity when microflow was used, but they might have cherry picked that compound after extensive testing of many compounds.

[sav]

How do feel about microflow?

The "microflow" is good choice (if you're looking for a higher sensitivity) with flows 10 - 100 ul/min and standard API source (standard ESI etc.). The best choice are 0.5 - 1 mm ID columns.