by
lmh » Fri Aug 07, 2009 10:01 am
MRM is usually applied when there are several analytes being measured, so a list of parent and fragment masses have been specified, while SRM is often used to refer to just one parent and fragment.
HOWEVER, IUPAC have recommended that the term MRM not be used. I think the reasoning is that "multiple reaction monitoring" ought to mean measurement by monitoring multiple successive fragmentations, i.e. an MS3, MS4 or whatever ion. For example, instead of using a triple quad to look at 493 --> 212, you'd use an ion trap or a hypothetical "pentuple quad" to look at 493-->212-->115 (something I don't believe is done).
Profile data is data collected as the detector saw it: in a scan, the intensity will rise and fall again in some sort of peak shape, hopefully centred on the correct mass. The profile isn't especially useful because the shape of the peak is a feature of the instrument, not of the chemical being analysed. Therefore many instruments reduce the whole peak to a single line of height equal to the area under the peak, and centred on where the correct mass ought to be. This is a centroid. Centroid data make much smaller files.
I could have a huge rant about the huge file-sizes of some manufacturers.
