Peak after solvent delay

[Laura._]

Hi,
I use GC Agilent 6890N with MS, last time I occured peak after solvent delay. I changed liner, septum, when I change the time of solvent delay - doesnt matter if earlier or later - the peak elutes after that. Could it be caused by dirty ion source? Or do you have any other suggestions?

Thx a lot

L.

P.S: I use 0,7 ml/min, column HP-5MS,it was also changed - described peak behaviour was the same.

[James_Ball]

Hi,
I use GC Agilent 6890N with MS, last time I occured peak after solvent delay. I changed liner, septum, when I change the time of solvent delay - doesnt matter if earlier or later - the peak elutes after that. Could it be caused by dirty ion source? Or do you have any other suggestions?

Thx a lot

L.

P.S: I use 0,7 ml/min, column HP-5MS,it was also changed - described peak behaviour was the same.

What masses are you seeing in the peak?

If it is just a spike when the filament turns on then it could be a slight contamination in the carrier gas or column bleed that builds up on the filament when it is off the is released when the filament heats up. If it is mass 44 or 40 then suspect some air or just CO2 and Argon impurities in the carrier gas. If you see mass 207 then it could be column bleed that is accumulating after the filament turns off and the oven is cooling back down after a gradient run. If the spectra matches your injection solvent then it is just some solvent had adsorbed on the filament then flashes off once it turns on.

[Laura._]

There is mass 128,1 - it is like my first analyte - naphtalene, but that unrequested peak occurs in hexane, too. In solution with standard I can distinguish first peak and second peak with the same mass. I also tried solvent delay in 8 minute and hexane measurement and the same strange peak was eluted but with mass 178,1. I see always only second half of peak. Ion source is cleaned, autotune done (try to change filament or what could help?). It is not about new method, I didnt have similiar problem until now.
Thank you

Hi,
I use GC Agilent 6890N with MS, last time I occured peak after solvent delay. I changed liner, septum, when I change the time of solvent delay - doesnt matter if earlier or later - the peak elutes after that. Could it be caused by dirty ion source? Or do you have any other suggestions?

Thx a lot

L.

P.S: I use 0,7 ml/min, column HP-5MS,it was also changed - described peak behaviour was the same.

What masses are you seeing in the peak?

If it is just a spike when the filament turns on then it could be a slight contamination in the carrier gas or column bleed that builds up on the filament when it is off the is released when the filament heats up. If it is mass 44 or 40 then suspect some air or just CO2 and Argon impurities in the carrier gas. If you see mass 207 then it could be column bleed that is accumulating after the filament turns off and the oven is cooling back down after a gradient run. If the spectra matches your injection solvent then it is just some solvent had adsorbed on the filament then flashes off once it turns on.

[James_Ball]

Does this peak appear if you start the run but inject nothing? You can remove the syringe and do a run that way so it doesn't inject anything. If it still appears then it is some residue that is adsorbing onto the filament and evaporating off once the filament heats up.

Cleaning the source will only help if there are some carbon deposits near the filament adsorbing the compound. How old is the column? Could it be the stationary phase is beginning to break down and bleed off onto the source?

Another cause could be a high boiling compound that is being trapped on the column at the end of the run and coming off at the beginning of the next run. If that is happening then you need to extend the hold time at the end of the analytical run to elute that compound before the oven cools down again.

[Laura._]

Also when I start run without injecting solution, it appeared.

I assume that it shouldnt be caused by column, because it was changed by service technician and its new ( same peak was eluted using old column).

I use "old method", I didnt have problem with it until now.... so it shouldnt be caused by insuffiecient hold time, I think...

Does this peak appear if you start the run but inject nothing? You can remove the syringe and do a run that way so it doesn't inject anything. If it still appears then it is some residue that is adsorbing onto the filament and evaporating off once the filament heats up.

Cleaning the source will only help if there are some carbon deposits near the filament adsorbing the compound. How old is the column? Could it be the stationary phase is beginning to break down and bleed off onto the source?

Another cause could be a high boiling compound that is being trapped on the column at the end of the run and coming off at the beginning of the next run. If that is happening then you need to extend the hold time at the end of the analytical run to elute that compound before the oven cools down again.