I-Class SM Carryover Issues?

-Blank after high sample shows significant CO (almost as close to LOQ), however, an air blank immediately after high sample has less CO (preferred outcome) and a consecutive sample blank after the air blank shows higher signal than the air blank. 
-Needle, sample loop, needle seal, injection pod and syringe all replaced. 
-Tried increasing wash too.
-SNW=MeOH; SNW=0.1%FA+10%MeOH in Water
Anyone have any ideas as to where the CO might be coming from? The same method with the same wash had not been producing this.


  • Hi Aashish,
    I'm sorry that it has taken so long for anyone to respond.  Has this issue been solved?

    If not, I'd suggest that an "air blank" doesn't really give much information about carryover.  It might be easier to troubleshoot by doing these things:
    • Zero volume injection - use normal method parameters but inject 0uL
    • Mobile Phase injection - use normal method parameters but inject a solvent blank (if you are running a gradient, use a mixture of approximately the midpoint of your gradient
    • If this is a gradient method run a "double gradient within the same injection.  For example if your gradient is 0% organic to 100% organic over 5 minutes create a method that looks like this:

      0.00 min 0%A 100%B
      5.00 min 100%A 0%B
      5.10 min  0%A 100%B
      6.00min 0%A 100%B
      11.00min 100%A 0%B
    These all tell you different things about the carryover peak and would be useful in troubleshooting.

    This article might also help (if you are using an Alliance System) - https://support.waters.com/KB_Inst/Chromatography/WKB64313_How_to_handle_LC_carryover_injector_carryover