BFB tuning problems

[hpuser48]

Our regular volatiles analyst is out this week so I have temporarily stepped in. We are running our samples on an old HP system 5890GC/5971MS w/P&T. We inject the BFB manually. The only problem ion is 175 which has a very erratic response compared to 177. Sensitivity is not a problem as there are plenty of counts and the threshold is not set too high. I have adjusted peak widths & corrected mass axis. The PFTBA scan looks a bit different from that which I normally see while operating our SVOC instrument(lower 219 but higher 502) but not totally abnormal. The system is very tight and there is no evidence of a leak. From the run logs I can see that our regular analyst has been having trouble with BFB for a while. The source has not been cleaned for a few months but it does not appear that very many samples(or particularly dirty ones) have been run. The multiplier voltage is around 2400 so it is approaching the end of its life. Any suggestions? TIA

[chemtexpps]

Lower the peak width or clan the source and Re tune the instrument.

[hpuser48]

If you will read my original post again please take notice that I *have* adjusted the peak widths. The 175 ion is present--just not at or near the apex of the peak. I only need to run one set of samples. The regular analyst can do the maintenace when he returns.

[Steve Reimer]

I have had a similar problem with a much newer instrument. For me it was 176/174 ratio. It's the bromine isotope ratio.
The fix according to Agilent was a change of the multiplier. If it's running @ 2400V it's past time for a change. If you are just trying to get through one sequence you may be able to string it along but that could be what your regular analyst has been doing.
Good Luck

[Bigbear]

What tune do you use? A manual tune or the canned BFB tune. Do you set the peak width to 0.5? On the 73's there is a way to set the 219 width, this may help if it' s available on 71's ( I've never run one).
The EM voltage may go down with a cleaning.