Chromatography Forum

Hello all,

Setting up anew instrument to run FAMEs on a aglient 7890 with a single MS. For some reason we are getting a decent tail on the solvent peak and the whole run has background noise which MS is Dichloromethane.

I was wondering id there was anything I could do to get rid of it. The solvent is Dichloromethane but previously I have used Chloroform, hexane or Dichloromethane as solvents and never seen this on other machines.

Is this to do with using Dichloromethane? I have never seen this before but it could be something to do with this new machine.

Cheers for any help

Matt

Check for dirt and bits of septum in the inlet, and its probably worth changing or cleaning the split vent line - Agilents are susceptible to backflow form the split line to the inlet.

Peter

If you imported the method, the setting may have become corrupt,
I suggest checking that the Split/Splitless settings are functioning,
and that the time delay to purge flow to split vent is set and working
with adequate flow for the rest of the duration of the run.
Also check that the septum purge hasn't been turned off during the
importing of the method.

kind regards
Alex

Are you using split or splittless injection?

What is your injection port temperature?

What is the starting oven temperature?

What is the injection volume?

Thanks for all the help

Will look into it

for the questions

Are you using split or splittless injection? Split (but we still see it in splitless) 25:1 split (should I increase the split or go to splitless?)

What is your injection port temperature? 260oC

What is the starting oven temperature? 140oC

What is the injection volume? 1 ul

Cheers for the help

m

Thanks for all the help

Will look into it

for the questions

Are you using split or splittless injection? Split (but we still see it in splitless) 25:1 split (should I increase the split or go to splitless?)

What is your injection port temperature? 260oC

What is the starting oven temperature? 140oC

What is the injection volume? 1 ul

Cheers for the help

m

If you have enough sensitivity at 25:1 then that is what I would stick with, it will keep things cleaner longer.

At 260C and if your head pressure is about 8psi then the vapor volume should be less than 500ul for DCM solvent so unless you are using a 2mm ID liner it should not be backflashing. For it to be hanging around that long, it must be adsorbing onto something. As mentioned above it might be a good idea to replace the split vent line, which is the copper line running from the split vent on the weldment to the rear of the instrument. You can clean them with solvent, but if you have some precleaned tubing for instrument gas lines and the nuts and ferrules just use some of that and replace it. When you have it off, clean the hole from the split vent into the injection port with a pipe cleaner and solvent also to make sure no high boiling components have collected there. Also be sure the insulating cup is on the bottom of the injection port where the gold seal is. I have seen many people leave that off for convenience(myself included) but it does help eliminate cold spots that can cause problems like what you are having.