Meaning of the term 'MRM'

[thohry]

Hi all,

In LC/MS there are MRM mode in which the Q1 select parent ions then fragment then select product ions for detecting. What I am not so clear here is the term MRM. It seems to have little meaning to do the process.
Say, in single MS, we have SIM mode (selected ion monitoring), it is very clear.
I am sorry for this kind of question, English is not my mother tongue.

Thanks.

[PeterS]

In LC-MS/MS MRM stands for Multiple Reaction Monitoring. It means that you set Q1 and Q3 to a fixed value while measuring the intensity during some time.

[lmh]

But despite its common use, IUPAC disapprove of the abbreviation MRM. They argue that Multiple reaction monitoring implies you are using multiple reactions to monitor a single analyte, i.e. you're looking at the transition A --> B --> C rather than just A --> B.

I can't remember what they recommend instead. I think SRM is OK (single reaction monitoring, as opposed to SIM, single ion monitoring)! No one doing SIM seems to have felt obliged to coin the term MIM!

And if you listen to IUPAC you have to differentiate between isotopologues and isotopomers, and I have yet to meet a mass spectroscopist who knows the difference without looking it up.

[thohry]

But despite its common use, IUPAC disapprove of the abbreviation MRM. They argue that Multiple reaction monitoring implies you are using multiple reactions to monitor a single analyte, i.e. you're looking at the transition A --> B --> C rather than just A --> B.

I can't remember what they recommend instead. I think SRM is OK (single reaction monitoring, as opposed to SIM, single ion monitoring)! No one doing SIM seems to have felt obliged to coin the term MIM!

And if you listen to IUPAC you have to differentiate between isotopologues and isotopomers, and I have yet to meet a mass spectroscopist who knows the difference without looking it up.

I see your explanation is informative. Could it be that the multiple reaction means the ions/species have to go through the ion source and then the CID

[Loekie]

MRM and SRM are exactly the same. indeed the IUPAC nomenclature is SRM (Selected Reaction Monitoring).

The fragments that are measured could be from multiple reactions in the colission cell they don't have to be all single reactions. The fragmentations of ions happen over the full length of the collision cell and a product ion B might fragment further into fragment C.

[lmh]

yes, I've never understood why we need the both of the terms MRM and SRM, and I'd be happy to stick with IUPAC's preference were it not for the fact the entire proteomic world seems to want MRM. But they think they invented the method anyway...

[Christian Eckhoff]

MRM is a term that is used by Applied Biosystems, supposedly to set them apart from their competition. It is an invention of their marketing. The correct term is SRM. When you monitor multiple transitions simultaneously you will several SRM channels, just as would have several SIM channels on a single quad (or have you ever heard of MIM??).
Source: The Mass Spec Desk Reference book by David Sparkman (highly recommended, as is his course in Stockton, CA)