5 Replies Latest reply on May 8, 2018 9:31 AM by dannymobbs

    Peak tailing in SFC-MS (while good peak shape in SFC-UV)

    xiaoz

      I was running a SFC method for separation of chiral isomers. The method works very well and we got very good peak shape when using UV as the detector. But when we use the exactly the same method and switched to MS as the analyzer, we have very significant peak tailing. Is there any suggestions how we can improve the peak shape in SFC-MS? Really appreciated!

        • Re: Peak tailing in SFC-MS (while good peak shape in SFC-UV)
          jhagel

          How does the tune look?  Also the spray?  Check the nebulizer needle and see if it needs to be replaced.

            • Re: Peak tailing in SFC-MS (while good peak shape in SFC-UV)
              xiaoz

              Thank you, jhagel. The tune looks good. The mass spec is working fine. We got very good chromatogram and signal on another set of chiral isomers on the same SFC-MS system. Also, for the set of chiral isomers that have peak tailing issues, we tested on 2 different mass spec systems (a QTOF and a tripleQ), and they both showed the same poor peak shape with significant tailing. So I think the SFC is good by itself and the mass spec is good by itself. It looks like it is something on the SFC to MS interface and it is compound dependent. Has it been seen before that certain compounds may have this type of peak shape issues on SFC-MS? Is it possible something related to the depressurizing of CO2 at the interface? I am very new to SFC-MS and any suggestion is appreciated!   

                • Re: Peak tailing in SFC-MS (while good peak shape in SFC-UV)
                  dannymobbs

                  Further to the good advice from jhagel, I have a couple of questions about your configuration. How is the setup between SFC and MS - do you have LC make-up flow tee'd into the SFC flow before the BPR? Normally a make-up solvent would be methanol with some MS compatible modifier.

                   

                  If you have no make-up or the make-up is tee'd in after the BPR, what you observe is normal. It is not compound specific and is related to the behaviour of CO2 after the BPR. We have a specific SFC-MS splitter kit (p/n G4309-68715) which allows split flow and full flow into the MS.

                   

                  If you could send a plumbing diagram or photograph of the setup, we could see exactly what you have there....

                    • Re: Peak tailing in SFC-MS (while good peak shape in SFC-UV)
                      xiaoz

                      Thank you, @dannymobbs. We have a make up flow of MeOH/H2O 90/10 with 0.4%FA running at 0.5 mL/min (mobile phase flow rate of 2.5 mL with 11-30% of ethanol gradient). I just checked the instrument and we have the splitter kit (p/n G4309-68715) installed with the plumbing for the full flow as indicated in the Splitter Kit Technical Note.

                      I am running 2 sets of chiral isomers (set A and Set B). The SFC-MS works very well for set A with good peak shape, while set B has the peak tailing issue. I tried to run set B with the SFC method of set A and still got significant tailing. This leads me to think about some kind of chemistry is happening at/after BPR and before mass spec. The difference between set A and set B is that set A has a ester group while set B has a carboxylic acid group, not sure if there is something related to the acidic functional group...

                        • Re: Peak tailing in SFC-MS (while good peak shape in SFC-UV)
                          dannymobbs

                          Ok, so you're well set up and doing well with the system so apologies if my previous comments/questions were a little 'basic'....

                           

                          Do you have any MS information about compound set B? By that I mean, do you obtain the masses you expect for the isomers or are they changing somehow (maybe forming dimers). My only thought is that they could be interacting with the material in the flow path between DAD and MS (since I think you said that UV peak shape was ok). If this is the case, it would be unusual to say the least. Did you try a different additive in the make-up solvent (for example ammonium formate)?