Hi!
I have an oral exam in a course called Inorganic Instrumental Analysis tomorrow, and there are some questions that I just cannot find the answer to. Please do not believe I am merely "doing it the easy way" by asking here, I have been thinking a lot about it and been trying to find some literature.
1) Why does ICP-MS have lower detection limits than ICP-OES? Is this question true for all elements, or is it more like "in general, or on average, ICP-MS will give you lower detection limits"?
Firstly, if ICP-MS has LOD, this tells me that the MS instruments handle background noise better than OES instruments; LOD is after all a multi-plum, usually 3, of the blanks' standard deviation.
The two measures I can recall for controlling background in ICP-MS, are these: Ion lenses right after the cones ensure that only positive ions are allowed into the quadruple or the reaction chamber. And the electron multiplier is positioned off-axis to reduce continuous background. Anything else I should know? (there probably is!)
In OES, however, elements can have numerous emission lines. Background correction is more "manual" than for ICP-MS. One- or two-point background corrections are sort of "user-dependent". Reflections in the mirrors can cause background noise. Chemometrics (for example Perkin Elmer's Multicomponent Spectral Fitting, MSF) can give good results with a complex background.
So, am I onto something here? Will this make sense at the exam?
I appreciate any *delete me*
Anders