Ghost peak FOCUS GC Thermo Finnigan

[Serge Robert]

I’m new on this forum, perhaps someone can help me with the following GC ghost peak problem:
I’m working with a Focus GC Thermo Finnigan in spitless mode with helium as vector gas and a FID.
In the middle of my chromatogram, I’ve a very disturbing ghost peak, that’s a beautiful (almost Gaussian) peak at the same retention time. When I change the method, the retention time of this peak change also.
I’ve tried the following test without any success:
Solvent : Ethanol (different quality), Ethylacetat, Methanol, IPA…
Split and Splitless
Column : DB17 or Uptibond 5 Premium
Cleaning of detector (perhaps not optimal)
Different kind of septa (injector and vials)
Plastic or glass pipette
I’ve already changed syringe and glass liner but always with the same article number

I’ve always the same ghost peak. I think know that’s coming from my equipment and probably from injection. If someone has got an idea, that’s really welcome.
Thanks in advance

[xxx]

T ry to make a run without injecting,to see if the peak appears.

Did you try with another column

What are your oven program,column flow,temp etc....

Bye

[dcobice]

Hi in my opinion, first clean the column at least 2hours at 260-280 degrees then try to clean the inyector port,with an increase polarity solvent gradient ultrasonic cleaning.If you used a silanol coating,please take off.If i understand what you told me this impurities was in your system and perhaps its an artifact peak of yuor GC system.What about the detector?? Its clean??

D

[Serge Robert]

T ry to make a run without injecting,to see if the peak appears.

Did you try with another column

What are your oven program,column flow,temp etc....

Bye

Hello XXX
Thank's for your answer
- That's a good idea to make a run without injection to see if it's coming from injector or detector . I'll try tomorrow (Friday) and I'll give you the results.
- This column is a new one and I've already tried an other one.
I've tried already differents methods with the same problem.
- My method is:
Column Uptibond 5 premium (5% phenyl-95% dimethylpolysiloxane)
Lenght 30m: ID0.25mm; Film 0.25micro
Injec 200°C (splitless mode)/ Detec 280°C
Carrier gas He (constant pressure 300KPa)
Split flow 100ml/min; Splitless time 1min

Oven 40°C - 2min
5.0°C/min until 140°C
2.0°C/min untill 190°C
10.0°C/min until 270°C
Injected volume 1micro
Thanks a lot and bye

Serge

[Serge Robert]

Hi in my opinion, first clean the column at least 2hours at 260-280 degrees then try to clean the inyector port,with an increase polarity solvent gradient ultrasonic cleaning.If you used a silanol coating,please take off.If i understand what you told me this impurities was in your system and perhaps its an artifact peak of yuor GC system.What about the detector?? Its clean??

D

Hello dcobice
I've already cleaned my column, it doesn't come from this .I'll first try the suggestion of XXX (do a run without injection) to understand if it's coming from injector or detector. Following your advice, I'll clean after the good part of my GC.
Thanks a lot
Serge

[Serge Robert]

Hi
I did a run without injection and I still see my favorite ghost peak. I know it doesn’t come from the column (because I tried already an other column) so it comes from somewhere between the injector (liner…) and the detector. What should be the best to clean first ?

[xxx]

Hi

Is your ghost peak similar in width with to the nearest eluting ones?
If it is wider it's carry over from a previous injection,or carried out into the column with carrier gas.

In your case if you still see the peak without injection,you may have a contamiantion of your gas line or injector....
Try to clean it first.

Do you have a second injector installed with this gc,on column for ex....
or do you have a second gc with the same configuration?

[CE Instruments]

Dear Serge
If the peak appears without an injection it must already be in the GC. This points to one of the following.
1 Something in the injector. Cool GC, remove the cover and heat insulation from the bottom of the injector and unscrew the large nut that allows you to remove the base of the injector. Check to see how much graphite has been pushed into the connecting nut, has it collected in the bottom of the injector ? If anything is present this is where you will find it. Clean and reassemble.
2 You/someone has tried to inject too large a volume and something has made it back down the carrier lines. Solution heat the detector to 450C using an old septa and just a restrictor instead of a column. this will bake the injector, note after doing this the septa will have melted and you will need to clean the injector/liner and replace the septa. If contamination is very bad you would need to get Brechbuhler your local agent to replace all the lines to the pneumatics module.
3 You are introducing your peak with your carrier gas ? Do you use filters, they could be the cause ? Do any other GCs uses the same gases ?
4 Are you using the correct septa, what temperature is the injector at ? Remember the Carlo Erba/Thermo injector is heated over its whole length and the septa will be exposed to the temperature you set unlike other manufacturers. If transferring a method from another GC you should try to use an injector temperture 20C below the temperture used on other systems.
Good luck.
Note CE Instruments Ltd are fully factory trained in the service of Thermo/Carlo Erba GCs if you are unsure about any of the suggestions please arrange for a qualified enginer to carry out the above suggestions, unskilled personnel could cause damage and CE Instruments cannot be held responsible.

[Serge Robert]

Hi
I’ve checked if there was something in the injector. I removed everything and I’ve seen that the terminal fitting was quite dirty. I’ve changed it with a new one and I’ve cleaned everything but even after an injection sequence of 12 hours, I see the same beautiful peak (not from a previous injection) at the same retention time and more or less the same area.
The second point seems to be for me a good “trackâ€

[xxx]

Anyway it's better to hold the detector temp 10-20°C above your oven final temp to prevent condensation....

But if you see a peak with a normal peak shape,it passed trough the column,and could not ,from detector coming...

A contaminated detector come noisy.....

You problem is contaminated carrier gas lines.

I assume CE Instruments has written a little mistake :

"2 You/someone has tried to inject too large a volume and something has made it back down the carrier lines.
Solution heat the INJECTOR to 450C using an old septa and just a restrictor instead of a column. this will bake the injector, note after doing this the septa will have melted and you will need to clean the injector/liner and replace thsepta. If contamination is very bad you would need to get Brechbuhler your local agent to replace all the lines to the pneumatics module "

[JI2002]

First, the column head pressure (300 Kpa) is too high for a 30mx0.25mm column, the 100 ml/min split flow is also kind of high.

How about set the injector temp to room temp and make a blank run without injection? If the ghost peak is still there, I don't know what the problem could be. If it goes away, it's most likely caused by injector.

[Serge Robert]

Hi Everybody

I’ve heated my injector (and not my detector as I wrote before) to the maximum allowed temperature 375°C and I still have the same problem . I take now contact with local agent and I will write the results on this forum.
Thanks to all of you