Chromatography Forum

Apart from the obvious MS/MS capability of the triple quad and its higher price, what are it's disadvantages compared to a single quad? Is a single quad generally more rugged, is it more sensitive, does it do better quantitation, is it easier to operate/maintain and what about the linear range?? This would be in general terms and for MW < 800.

Is the single quad...

more rugged? Not to my knowledge.

more sensitive? No, less sensitive due to lack of MS/MS capability. But perhaps you want a comparison between a single-quad and a triple-quad operating in Q1 Scan or SIM mode (i.e. acting as a single quad). This would depend on which instrument brands you were comparing, and I'm afraid I don't have enough info to make a general statement. I can tell you that I have used three generations of triple-quads in Q1 modes, and they all perform adequately in this function. Of course, the older generation instruments are less sensitive. But I never found myself wishing I had the latest single-quad.

better quantitation / linear range? Not that I know of.

easier to operate / maintain? Well, there are fewer things that could go wrong with a single quad, in theory. Plus, on a single quad, the operator doesn't have to worry about setting up MS/MS conditions. So yes, easier to operate, until you have an interference problem due to lack of specificity.

Disadvantages of triple-quad over single: larger physical size, cost.

I'll complete MG reply...

As MG say the triple quadrupole operating in MS/MS is more sensitive than a single quadrupole and it has a higher linear range (assuming that you compare a molecule that fragments well... there is a minority of compounds that do not fragment well).

If you want to compare the single MS capability of these two instruments then... whenever you add quadrupoles you losse ions so I would expect that a single quadrupole would be more sensitive in the MS only mode than a triple quadrupole. But again it depends on the manufacturer, in other words a single quadrupole from the same manufacturer it should be more sensitive in the MS only mode than their triple quadrupole due to the inhereted loss of ions each time you add more ion-optics...

Although you seem like searching for reasons to buy a single quadrupole, my advice would be to buy a triple quadrupole if you deal with compex matrices (i.e. plant extracts, biological fluids etc) and/or if you need to do structural identification (for that ion-trap would be even better).