Just a quick questions regarding GC/MS

[Spliff Politics]

Hi there, so as the title says, just a quickie. Was just curious if a standard GC/MS test can differentiate between structural isomers? To be exact here, I am talking about 3-MMC and 4-MMC. Now I'm not particularly chemistry literate, so please bare with me. I was always under the impression that it could not, due to the two drugs sharing the same molar mass. On the other hand, this paper here seems to say otherwise - https://academic.oup.com/jat/article/40/7/546/2364114

"3-MMC was only identified by GC-MS (Fig. 1), which allows the discrimination with mephedrone that is not the case with UPLC gradient and for better sensitivity was quantified by UPLC-MS-MS method." I can't quite understand if this is saying that they could do it with a standard GC/MS or whether further reagents/tests were required.

Again, as I said earlier, I'm not particularly chemistry literate, so I would really appreciate it if anyone could answer this without getting too complex (apologies about that).

Thank you very much for your time!

 

[sekio]

With the right GC column, yes, you can get seperation, (especially with a cyclodextrin column) but the MS spectra will be very similar if not nigh indistinguishable.

 

[adder]

What the authors say in the article is that they used GC-MS to differentiate 3-MMC from 4-MMC by their retention times because they were unable to do so using UPLC, which they used for quantitative analysis due to better sensitivity. Using UPLC-MS/MS they carried out quantification of 3-MMC, MS/MS stands for tandem mass spectroscopy which consists of multiple mass spectrometry selections (i.e. after the first selection selected ion(s) is/are subjected to further fragmentation and product ion(s) are detected, if we stop at this point, we have MS^2, but the aforementioned product ion(s) can be fragmented one more time, then you have MS^3, and so on), in this case they used MRM (multiple reaction monitoring) within a narrow range of 178.1-160 m/z, i.e. ions with m/z within that range were subjected to secondary fragmentation and product ions detected.

So, to cut it short, 3-MMC can be differentiated from 4-MMC using GC-MS and they did so, the other analytic method was used to quantify 3-MMC.

 

[Beenhead]

What the authors say in the article is that they used GC-MS to differentiate 3-MMC from 4-MMC by their retention times because they were unable to do so using UPLC, which they used for quantitative analysis due to better sensitivity. Using UPLC-MS/MS they carried out quantification of 3-MMC, MS/MS stands for tandem mass spectroscopy which consists of multiple mass spectrometry selections (i.e. after the first selection selected ion(s) is/are subjected to further fragmentation and product ion(s) are detected, if we stop at this point, we have MS^2, but the aforementioned product ion(s) can be fragmented one more time, then you have MS^3, and so on), in this case they used MRM (multiple reaction monitoring) within a narrow range of 178.1-160 m/z, i.e. ions with m/z within that range were subjected to secondary fragmentation and product ions detected.

So, to cut it short, 3-MMC can be differentiated from 4-MMC using GC-MS and they did so, the other analytic method was used to quantify 3-MMC.

You almost got it its not a mass window, rather a MRM reaction.

MRM, which is multiple reaction monitoring is like SIM (selected ion monitoring) mode except that you are looking at a CID (collision induced dissociation) reaction in MSMS mode. So basically, they sequestered 178.1 m/z in the collision cell and performed CID on it. Then they looked for 160 and 144.9 M/Z in the product ion spectrum (annotated 178.1-160,144.9) and they also did another reaction for 199-164.9 transition. These two were to Identify 3-MMC. They looked at a couple other transitions for 3-MMC for quant purposes.

 

[Spliff Politics]

Thank you very much for your replies everyone, it has been extremely helpful .