problem with auto-tune results on GC/MS. Bad ion ratio

[frimouss60]

Hi,

excuse me for my bad english, I hope that you can understand me...
I work on GC/MS Thermo focus GC/DSQ 1
I have cleaned my source and my prefilter, my gas is HE, my column 5%diphenyl.

When i make an autotune with the FC43 my ion ratio is not good.
ion 69 = 60-70%
ion 131 = 20-30%
ion 219 = 100 %....

normally, I would have
ion 69 = 100%
Ion 131 = 40-60%
Ion 219 = 40-60%....

I don't understand why i have these results...Is this error could be imput to my column choice ? before i used a 100% dimethyl polysiloxane.
If you have an idea..

Thanks.

[AICMM]

frimouss60,

Seriously doubt it is column related but if you want to check, blank off the inlet nut to the mass spec and try your tune again. Eliminates column issues, eliminates helium flow rate issues and eliminates upstream leakage issues.

Considering the last thing you did was a source clean, I would suspect a part put in the wrong way or contaminated or cracked or a missing electrical connection to a lens or something along those lines.

Best regards.

[frimouss60]

thanks for your answer.

I have checked all my connections and cleaned again my MS but no change.I have checked too all the temperatures, flows...

I think like you about my column but all ideas are a good way for finding...

Yesterday, i make autotune and the results was good
ion 69 =100%
This morning I just have runned a maintenance tune and the results are always bad...
ion 69=68%

there is just one thing the prefilter offset when my tune is good it's 4.7V
and when it's bad it's 15V
I don't understand this ! nothing has changed during the night no sample, no blank,nothing ...maybe a poltergheist ?

I hope someone to help me...

and thanks again AICMM.

[leadazide]

One thing you have to be aware about on Thermo DSQ's is that they don't auto-tune for maximum signal on 69, but maximum signal on what ever mass gives highest signal.

What kind of intensities are you getting? Are the intensities for all the masses lower when mass 69 isn't 100%?

If it is really important for you to get mass 69 as the 100% mass there is a setting in one of the menues where you can force it to tune the 69 mass for 100%. But beware that this might effect your sensitivity on all other masses as it forces the 69 mass to be highest even though other settings would give better sensitivity on the other masses.

Hope this helps!

[frimouss60]

hello,

leadazide

Yes when my ion 69 is 100% all my other masses are lower :
69 =100%
131 = 30
219 = 40
and other...

Sorry i'm newbie in GC/MS...It's difficult for me i just have one week training and i learn by myself.

I have resolved the problem this morning by adding parameters in my tune. . I 'm so stupid...
I've read all my old tunes and pointed out that in the past i used some parameters in my tune file. But, I had lost them since a few weeks. how ? i don't know

I hope it's really the cause of the problem.

I shall keep posted you about this.

Thanks.