Hello everyone
Is the MS/MS instrument capable of distinguishing between stereoisomers in general? if so, how?
And, if I'm working on two stereoisomers drugs (E and Z), how can I separate them using LC-MS/MS?
A bit more info would be helpful, but ion mobility MS is the first thing that comes to mind..
Hi Ibrahim,
Thanks for your question, I think some more information would be required for a more specific answer but I can give you a general overview to get you started.
When performing LC-MS/MS normally you have the ability to separate particular compounds by there specific mass. This means that when compared to techniques such as HPLC you will generally be able to make shorter run times as you can separate individual masses. However, when you have something such as an enantiomer/isomer which will have the same mass and generally the same behavior in column, you will need to separate these chromatographically.
Depending on the molecule and how it behaves in various columns, you may have a column in house that may be able to be adapted to your needs. Without knowing the specific compound and extraction I can't give any specific advice on which column is required for your application.
In general, the first approach would be to extend your run time and reduce your flow rate to increase the amount of time in column, a lot of times while maybe not being as quick as a chiral column, this can often solve your issue and is a much cheaper option. I would also switch (if you haven't already) to using a methanol mobile phase (e.g. MeOH/HCOOH (100/0.2, v/v)) this will improve interactions in columns such as PFP, Phenyl and Bi-phenyl columns and many more.
If you aren't able to separate using the above and depending on the compound, you may need to invest in a chiral column. These columns will separate isomeric and enantiomeric molecules through specific interactions. Chiral chemistry is more in-depth than would be possible to go into here but if this is a route you want to take then I would suggest contacting phenomenex. They have a chiral column service that I have used commercially before when dealing with difficult separations, as they know the various columns inside and out they can make very good judgements on your specific column needs and will generally come on site to test these for you. The columns are much more expensive as they have specific applications but it may well be worth it based on your needs.
Once you have separation of the isomers you should be able to identify them easily and produce a method based on this.
I hope this helps.
Also check https://www.tandfonline.com/doi/abs/10.1080/10826079508010430
https://www.sigmaaldrich.com/US/en/technical-documents/technical-article/analytical-chemistry/purification/faq
The only possibility to separate stereoisomers by using only MS capability is ion mobility mass spectrometry as indicated. There is a couple of instrumentation such as Drift tube ion mobility spectrometry, Low-pressure drift tube, Travelling wave (Waters), Trapped ion mobility spectrometry (Bruker), High-field asymmetric waveform ion mobility spectrometry (aka FAIMS / Thermo), Differential mobility analyzer (SCIEX)...On the other hand, it is also advisable to choose chiral separation mode (appropriate chiral LC column) and combining with any MS analyzer. Besides, the hyphenation of LC and circular dichroism (CD) detection is a useful analytical tool that can significantly facilitate the analysis...
It all depends on the configuration you have, molecules you are targeting.
Emir
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