gc/ms tuning

[Spectro]

Hi All,
My gc/ms had a problem on tuning. My BFB direct inject did not met the qualified standard. I tried to using bfb tuning and autotune offered by Chemstation but in vain.
Do you all have any suggestion.
Thank all.

[Omaejel]

Many times I have been able to ramp the parameters by hand and get things to tune. I like to set the 219 t0 around 40-45% of 69 ion and 502 to around 2%. Then set the peak widths and double check your tune.

[AICMM]

Spectro,

Post your tune and post your failed BFB. Instructions for this are in the Liquid Chromatography section. Best way for us to help you.

Best regards.

[Spectro]

hi all,
All the information are Emission 34.6, Repeller 24.26, IonFocus 79.7, EntLens 14.5, EntOffs 21.08. The BFB failed at the target mass of 75 as relative to mass 95. The results was 69.3 while the upper limit % had to be 60. I tried to manual lower the IonFocus. Unfortunately the mass 75 was OK, but the mas 174 was over the upper limit. Hope you all can give me any suggestion.
Thank all, Spectro.

[gpronger]

When manually tuning, you need to think in terms of the mass range you're attempting to adjust. Your BFB ions are 50, 75, 95, 174 and 176 (plus the M+1 ions). In PFTBA your best matches are (PFTBA ion vs BFB ion); 50 = 50, 69 = 75, 131 = 95, and 219 = 174 (at least that's how I think about it). Problems with the M+1 ions indicate (usually) a issue with you're peak width.

With your problem, I would go through the ramps and look to decrease the 219 ion without significantly changing the ratios to the other ions. I'd be monitoring 69, 131, and 219 only. If you can decrease 219 without changing the ratio of 69 to 131, you should be moving in the right direction.

Greg

[Bigbear]

What method are you running? We do EPA 524 and the limits for 75/95 are 30-80%

[Spectro]

Hi BigBear,
lucky you. I run EPA 8260 and the limit is 30-60%. My 75/95 usually be around 60-65%. Sometimes I made the IonFocus down and the 75/95 was lower than 60%. However the sensitivity was aslo down and it made my daily Standard low.
I'm really frustrated with the bfb tune.
Spectro.

[coombs_ryan]

Spectro

Try this... it's an Ap Note from Agilent titled BFB Tuning for Enviromental Analysis: Three ways to succeed.

http://www.chem.agilent.com/Library/app ... 4373EN.pdf

[Omaejel]

Around here we call 75 ion the ion of death. Generally when 75 ion is running too high we wind up cleaning the source. I have tried to get the MSD to tune after the 75 ion starts running high by manually adjusting the parameters, but have had very little success. I would clean the source and move on with life.

Has anyone else had much luck with getting the 75 ion to go back down when it starts getting high? I would love to hear how you have been able to get it back in line withough a good cleaning.

[coombs_ryan]

Have you tried tuning it down manually?

[Bigbear]

My instrument only works with a manual tune. I autotune then manually tune by:

Setting ion foccus to 140 then monitor 50/69 should be 0.8- 0.9% ( for me the gases work better witn 1%. Mess with IF to change this ratio.
Then set ions to 69, 219, and 502. Ramp emission current. Pick the maximun which increases the emission.

Then monitor 69,131,and 219. Mess with entrance lens and offset to get 131 ans 219 to about 50% of 69. Then up the EM to get about 600000 counts.

Works for me.

[coombs_ryan]

Yup... i do it exactlly the same thing... i haven't had a BFB fail any masses since starting to manually tune over a year ago.

[Bigbear]

Interisting. I don't know of many folks that tune like I. Do you also use the 6mm draw out plate.

Have you been working with Ron or Herb?

[coombs_ryan]

I've tried it but really found no difference. I did just buy an inert source though about two weeks ago and just installed it today actually in one of my instruments...

I also ran a calibration with another vendor and got some interesting results that i will have to duplicate some time over the weekend regarding the BDCM problem... i had an old source in there and so my sensitivity was going up and down which made my curves not perfect. Next week i should know more

[ahallberg]

When you say there is a problem with your peak width if 175 is failing I'm assuming that it is too wide. I'm having a problem getting 175 to show up at all. I've changed the peak width from 0.55 to 0.5 when target tuning (following the instructions in the Agilent article already mentioned in this thread). Any other suggestions to getting this ion to show up? We had the same problem this morning and I switched out the source with a clean one to no avail.

thanks!