Detection specificity ???

[Urzuz]

Hello all, first time poster here!

I was asked this question recently: In general, which type of detector is the least specific: UV/Vis, fluorescence, electrochemical, and MS ?

My answer was ED. Was this the correct answer ?

Thanks for your reply and please feel free to extrapolate

Urzuz

[tom jupille]

No single/simple answer to that. I'd probably choose low-wavelength UV or MS.

UV: All that's required for some absorbance around 200 nm is a double bond of some kind; pretty much anything except for alkanes, aliphatic amines, and aliphatic alcohols or thiols can be detected.

MS: you can monitor total ion current to be non-specific (also relatively insensitive), but the additional specificity is always there, so I suppose you could say this qualifies if non-specificity is considered an advantage.

Basically what's required for fluorescence is a structure that's rigid enough to prevent absorbed energy leaking off via vibrational transitions.That's a much smaller population than UV absorbers.

Electrochemical detection requires that the analyte be more easily oxidizable/reducible compared to the mobile phase. I'll defer to anyone with more electrochemical background as far as estimating whether the population of compounds that meet that requirement is larger or smaller than the lowv wavelength UV absorbers.

[DR]

I think that light scattering detection (not on original list) is the least specific as it will pick up anything and have the least variation in response as a function of the analyte's composition.

[tom jupille]

good point. (I was treating this as multiple-choice). You can also add RI (universal; more variable response than ELSD, usable with non-volatile buffers, but not usable with gradients).

And, if you want to go back a couple of decades, there were FID detectors (basically a GC detector with a moving wire or belt transport from the column outlet) and at least one IR detector (not usable with reversed-phase columns for obvious reasons). The FID could be regarded as the least-specific of the bunch, but it was not a roaring commercial success.

[Kostas Petritis]

Actually in terms of the most specific, I would choose the MS (so I disagree with you Tom . If you define as specificity the capability of your detector to analyze only the compound of interest among a mixture of compounds (matrix), the MS is the most specific, especially the triple quadrupoles when operated in SRM (or MRM) mode...

[tom jupille]

You're right, Kostas, but the point I was trying to make is that MS can be made non-specific if necessary. I'm not sure why you would want to do that, but . . .