BFB Tuning

[anabolic1980]

Hello!

Have a problem with BFB passing on the first/ second injection via EPA 624/8260B/ 524.2 parameters. It seems to always fail 176/ 174 ratio about 101-105. I have tried to adust the dynamic lens ramp ion 219 decreased by 0.1v increment. When evaluate BFB after decrease 219, the ratio 176/174 is now failing too low. I just cant seem to get this ratio in check. Peak widths around 0.5 for 69/ 219/ 502. Any help is appreciated what to adjust next. BTW, this is on a HP 5971 MS. Also, the mass for 69 reads about 69.15 and 219.05-219.15. Is that ok? or too far off for the mass assignements?

[Balderquell]

If a tune is going to fail, that's usually how it will go.

When was the last time you cleaned source?

What is your source temp and vacuum reading?

Here's some things you can try.

Check the column flow in your run method. If the flow is higher than 2ml/min, try reducing it to 1.0 to 1.5m/min. With higher flow, the MS has a harder time pulling a low vaccum.

Scan from 10 to 75 and look for water (ion pattern of 18, 17, and 16)nitrogen (28), oxygen (32), and carbon dioxide (44). Presence of these indicates a leak and will interfere. If these are all less than 10% of ion 69, you're ok.

Set target tune parameters as follows:

ion 135: 42% of ion 69
ion 219: 40% of ion 69
ion 502: 1.5% of ion 69

Peak width: .45

And then run a target tune. If the target tune will achieve these ratios, the mass spec is probably in pretty good condition, especially if you get a good response for 502 and it's isotope (abundance 10000 or higher).

You can also try increasing the EM voltage by 50 or so.

[anabolic1980]

Balderquell, thanks for the reply! Source was cleaned about month ago, but this tuning issue has been going on for months now. The BFB will eventually pass after a few runs, but mostly if I do a "manual" click on a certain area of the peak. In the past, it would pass with the just the chemstation BFB auto integration macro on the first run. The vac foreline is about 26mmtorr (normal for this system), the 18, 32 ions are less than < 2 % combined of ion 69. Column flow about 0.9 ml/ min ( I found with the 5971 a flow slightly less than 1 ml/min works best, maybe cuz the efficiency of the diff pump??). Otherwise, once the BFB does pass, the system runs fine. I just cant figure out why this certain ratio always fails high, then adjust 219 ( barely 0.1 v-0.3 v) and then fails too low. I just would like the system to pass with with the peak avg from the BFB macro as it did for years before. Maybe the peak widths at 0.49-0.51 are too wide??? THANKS !!

[AICMM]

anabolic,

I would re-adjust the mass axis since 69.15 is too far off the assignment. Also, don't worry too much about 502 (too heavy to worry about for VOA analysis) but look at 131 and 219 instead. Finally, I would make sure 219 and 131 are below 0.50 pW50 using the AMU gain and AMU threshold features. I never do use the adj219 just because I grew up on a 5970 and it was not an option.

Best regards.