Chromatography Forum

Hey fellow chromatographers!

Looking for some help with a 5973 that has been having difficulty passing BFB for Epa8260. Some details on the setup

Archon, Tekmar 3000, 6890GC, 5973ms(slow electronics). an old ms been in use for close to 8 years.

Purging bfb at 25ng for analysis. Maybe one in 5 runs will pass bfb. we are consistently facing issues with 176 and 174 ions. 176 being to large. Abundance on 95 is +40000 counts which I believe is pretty good. Cleaning the source makes zero difference in the pass fail rate. Re-automated tuning nothing. We have tried adjusting the tune manually (via the software's dynamic ramping) doesn't seem to make much difference. For me the tune looks good in the ms, peak widths are below 50% fc43 ratios look normal. I posted a pic below for review. Just hoping to see if any of you have some ideas. really any advice is much appreciated. let me know what i forget to mention. thanks


Couple things to note. EM is middle aged. Whole source has been replaced.
pics are worth a 1000 words so here are a couple.

this is the scan across the apex. ratios don't shift much on adjacent scans


this is the profile and ms tune info

How do you inject the BFB? Direct injection or a purged sample. EPA 524 states you can do a bfb check on not more than 25ng on column. If you are purging 25ng and splitting then you can increase the amount of bffb in your sparge vessel.

This 174/176 issue can really be annoying. Some instruments will just slip into this behavior for a while. Hardware steps like a new repeller and/or electron multiplier can help, but are not always needed.

I usually try varying the peak widths between 0.4 and 0.6 to see where it gets me. A lower repeller setting is better for resolution issues, though you normally are better off at 20 or higher for sensitivity and linearity. Sometimes varying the emission current works as well (20 to 60 is a useful range).

I ran into this problem with my 5975. The 174/176 ratio would go nuts at times with ratios varying by 10 to 15% between scans. No other symptoms of what was wrong.
An Agilent long timer suggested an upgrade to the triple axis detector. After that the problem went away. I don't think that was the fix but I never determined just what caused the problem.

Thanks for the tips guys. Its pleasing to hear this has been a problem for others. I am going to play around with with emission current and peak-widths to see if that helps much. As you did Steve, I have a feeling that we are going to be replacing the HED assembly, maybe try to clean it first.

cat4lyst,

I'm not sure if you've seen this document, or tried tuning your MSD without using the dynamic tune; but I figured I'd share it here since it's appropriate to the discussion.

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

Those are setting I would use on a normal run myself. I might increase peak widths up to about 0.55 just to keep the 173 and 175 from getting too high but if it is working that is ok.

You can play with the lenses and the Entrance Lens Offset dynamic setting to try and move 131 to be more abundant than 219, this sometimes helps with the 174/176 balance. Having 131 at 50% and 219 at 45% could fix the problem, will lower your high mass sensitivity a little but not too much.

It is definitely a common problem so you are not alone with this one. It can be just as aggravating as having mass 50 too low or mass 75 too high (usually by less than 1%).

If you have wiggle room on the number of scans across each peak you can adjust the sampling rate in the tune menu on the method page and get more samples/fewer scans across the peak which may help, just try to keep the scanning rate up above 2 scans per second.

Every now and then I have one where I just have to start evaluating every scan across the BFB peak to find one that passes since for something like 8260 it isn't set in stone exactly what scan must be chosen to evaluate. You can also average the scans across the peak and see if that works. But it is best to get things where it will just pass automatically each time if possible.