Pretreatment Method parameters in Empower

kdales,

I can see several potential issues with attempting to perform a post injection needle wash, especially if you are running a gradient LC method.

With your current program you perform an injection, which places the needle into the seat and the switches the valve to mainpass. Then you immediately switch the valve back to bypass for the wash, stopping the flow of solvent through the loop, needle, and seat. I suspect that will not be enough time to adequately flush your sample out of the sampler and onto your column. You can add a WAIT command and flush the injection path with however much solvent volume you think will be necessary to get your sample into the flow path. But then you must switch the valve back to bypass during the analytical portion of your run to perform the wash. This will cause a baseline disturbance, though if you can do it before the void volume time it might not affect things too much, but you would have to determine that experimentally. 

Now you can perform your wash, but your loop, needle, and seat are no longer part of the flow path, and if you are performing a gradient run they will not have their internal volume flushed with your organic phase (assuming you are doing reverse phase work) unless you again switch the valve back, which will cause another baseline disturbance and flush a slug of your starting condition eluent onto your column. Depending on where you are in your gradient this may not be desirable. 

You could just leave it in bypass until your last peak of interest comes out and then switch the valve back, but then you are mixing your starting condition eluent directly with your end run eluent composition. If you are using buffers that may not be the best thing to do.

I would suggest referring to the sampling sequence information that starts on page 10 of the user manual found here to have a full understanding of how an injection sequence normally works to help in making your injection program. 

As for removing the wash vial I believe you can use the NEEDLE command and tell it to go into the seat. This should return the vial to the tray and lower the needle into the seat. Then you would have to decide if you want to use a VALVE command to switch back to mainpass right away or how you would want to proceed.

Hello kdales,

I just wanted to follow-up to see if your questions had been answered. If so, please come back to the post and click Verify Answer on the best response so it will make the solution more visible.  If you still need help, just let us know and we would be happy to continue working with you.

Was there ever resolution on this issue? I'm encountering something similar on an agilent 1200, where a pretreatment program that worked for me with empower 3 - FR2 no longer works after upgrading to FR5. Now whatever I have programmed into pretreatment is ignored completely. The system just draws and injects sample as if no pretreatment was present