Agilent 5977 issues

[cjm]

Hi all,

Our lab has a 5977 doing purge and trap VOA analyses and for about a year it ran great, tunes held for a long time, chromatography was good, baselines were good. Now there's so much noise in the baseline it's difficult to reach necessary detection limits.

About two years ago it was taken apart for "routine" maintenance, source cleaned, filaments changed. It's never recovered from that day, and I'm trying to figure out what happened. I've cleaned the source a couple times now, changed filaments.

I just discovered something very strange. The transfer line looked bent. Like, really out of place, but it seemed to enter the transfer line socket on the source body ok. I took the whole transfer line assembly apart and it turns out the housing that holds the 2mm transfer line was the bent part. Looks like a manufacturing defect because the bend happened at a spot where two parts were welded. I can't determine if this has anything to do with the problems we're having.

I just rebuilt it and ramped lenses to see how everything looked. I CANNOT get any ions to maximize when ramping the repeller.

I changed the insulators and the repeller. Still, I cannot get 69, 219, or 502 to maximize anywhere along the ramp. I have no idea what to make of this.

[James_Ball]

Sometimes the max of the repeller is above the max that it will ramp to, not unheard of.

If it is not reaching a max, you can try to lower the emission current. Try doing one step at a time then reanalyzing the repeller ramp. I have a 5975 that after this time when changing filaments I dropped the emission current from 35 down to 17 before I was seeing the bell curve shape on the repeller ramp. The filaments also seemed much brighter so I figure the filament wire is a little different diameter on these new ones.

Another thing that can cause noise would be a small air leak, can be in any of the sealing surfaces and since the trouble happened right after a service it could be a tiny nick happened to the sealing o-ring on the analyzer or simply some lint is now stuck to it. Check around it by scanning with the calibration gas valve closed and spraying some Dustoff computer duster around every sealing surface, if there is a leak you will see it. Also put the tube of the Dustoff next to the column nut and direct it into the insulation where the transfer line enters the column oven. I found a crack in a weld on an interface that way. Sometimes you can get a small leak at the welds that hold the interface tubes together.

[cjm]

I dropped the emission current from 34.6 to 20 and I'm much happier with the ramp. I was always told never to touch that value so I wasn't familiar with the effects of changing. When I first looked at this instrument to fix the problem I figured something was very wrong if I didn't get bell curves on the repeller ramp.

Thank you for the advice on that. As for leaks, I will have to re-grease the analyzer door o-ring which I should have done last week, N2 is under 10% and as long as it's stable we'll run it. I should have no trouble locating leaks, canned duster is my favorite detector.

I'll send an update in a day or two on how we're progressing. Thank you for the help.

[James_Ball]

Prior to the 5972 the emission current was a fixed value, but with the more efficient filaments introduced after that they made it adjustable to compensate when there was too much ionization. If you have a problem getting the high masses to respond you can lower emission which will bias the fragmentation to the higher masses, increasing emission current will bias to the lower masses.

The one that should remain unchanged is the 70 electron volt ionization potential as that is where most library spectra is acquired at.

[Steve Reimer]

James,
Thanks for the explanation. When my repeller comes out high (>35V) I expect that my 176/174 ratio will be high on my BFB tune check. Now I know why.

[cjm]

BFB is passing now. Ion 50 is still a bit low (17%), I'm trying to play with it a bit and bring it up a few percent. The consistency seems much better than before, I wonder if bringing that emission current down has much to do with that.

[James_Ball]

It can, because you are less aggressively fragmenting and things are more stable.

m/z 50 can be a bear sometimes, if you do ramps using m/z 100 and compare that to m/z 50 then you can see what adjustments will give you the needed change for 50 vs 95 in the BFB. If you see a lens moves the two in different ways you might be able to eek out a few more percent for 50. Also if you are using the variable Ent Lens Offset you can tweak this by altering the setting for 131 to bring down 95 relative to 50, and the 131/219 settings can be used if you have a problem with 174/176. I normally take a BFB tune and then change the Ent Lens Offset to turn off variable then do a ramp on it with each mass in the list to find where they maximize, then use that to know what adjustment to do to tweak my final mass ratios.

[cjm]

I love using the entrance lens offset dynamic for my two 5975s and have great luck using them just as you do. I was trying to play with it on the 5977 but I swear there was no change when I altered the value for ion 50. I think I'm going to turn up the emission current slightly and see what comes of that. Ion focus and entrance lens ramps look good and I don't want to change those. More testing today....