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So I know the answer to this question varies widely across mass spec techniques, masses, and, of course, budgets, but my question is about the best case scenario for all of these variables (although I'm not really looking at proteins or anything of that size). I realize that the concept of depletion spectroscopy relies heavily on very sensitive mass spectrometers, and I'm curious about the lower limits of signal detection for such methods. Thus, I'm interested in the sensitivity, not resolution ("mass resolving power"), which seems to be a statistic that is difficult to find for most of the systems that I've looked at. Some related follow-up questions are what mass spectrometry methods can and cannot be used with depletion spectroscopy and what methods/manufacturers are the gold standard in the field of mass spec?

Thanks in advance for your answers.

Daisy Sophia Hollman
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Since there are no specialists in depletion mass spectrometry, I will try to answer in a more general way.

With depletion spectroscopy you look at a small variation of a large signal so what you need is not high sensitivity but signal stability and high dynamic range of the detector. I assume that you have a continuous stream of ions, otherwise pulse to pulse fluctuations of ion concentrations will be the major limiting factor. Probably, you won't need superb mass resolution so you would want to buy a quadrupole mass spectrometer - these are cheap, compact and there are plenty of companies that make them.

Dynamic range depends on the ion detector and since you would be looking for a wide dynamic range and stability with time, the very best choice is a simple Faraday cup. You can be sure that, whatever your experiment is, the sensitivity will be limited not by the detector but by fluctuations of your signal - most likely, by how stable your depleting factor is.

gigacyan
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