Troubleshooting low relative response on a mass spec. after source cleaning

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Boswell
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Troubleshooting low relative response on a mass spec. after source cleaning

I cleaned a mass spec. source the other day and after pumping it back down discovered that something terribly wrong happened.
Responses are around 10 fold lower than precleaning, isotope assignments are off and the entrance lens is at 0 when it usually runs around 14.
I've heard that maybe the quad. cap was nicked upon reinsertion of the source body. Any other ideas?

mbicking
mbicking's picture
Please give us more

Please give us more information about the type of instrument you have and the type of samples you are analyzing.

Also, please describe your "cleaning" procedure in more detail.

Boswell
Boswell's picture
I am using an Agilent 5973 GC

I am using an Agilent 5973 GC/MS. I cleaned the source with methanol and silica, then rinsed in methylene chloride twice then methanol.
I work in a forensic toxicology lab so it is derivatized samples that we are running; usually BSTFA.

mbicking
mbicking's picture
There are several

There are several possibilities, so let's look at some simple things first.

First, is this the first time you have cleaned this source, or is this just the first time you have had a problem?

Did you do any other maintenance during the source cleaining? (septum, inlet liner, gold seal, etc.) If so, check that those procedure were done correctly and that you have no leaks.

Check the position of the colum in the MS and re-adjust as necessary. It may be simple positioning.

Boswell
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I'm just thinking that it

I'm just thinking that it must be the quad cap. Is this what it looks like when on cracks or gets chipped upon source reinsertion? I've never encountered it.

mbicking
mbicking's picture
A also checked with my repair

A also checked with my repair expert and the other suggestion was that you may have switeched the wires for the entrance lens and ion focus lens (blue and orange, I believe). Try switching them to see if the problem goes away, and write back with a report.

Greg Pronger
Greg Pronger's picture
One of the ways to fairly

One of the ways to fairly easily check how your lens are working is to perform a parameter ramps on each of them (repeller, ion focus, entrance lens, entrance lens offset, and x-ray). It is usually pretty obvious if one is "mis-behaving".

Also, once you've solved whatever is causing your current problem, hard copy each profile when the system is newly cleaned and running well, and keep these around for reference (I tend to like to do this after every time I clean the source). They are then very good references as time passes and the system gets dirty.

Good luck with your problem.

Greg

Dr. Analytical
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Greg:

Greg:
Thanks for the extra information and suggestions. Please keep coming back. We need more people like you in this forum.

Boswell
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Thanks Greg. OK- here's what

Thanks Greg. OK- here's what I got:
Repeller: looks fine
Entrance lens offset: fine
x-ray- not familiar with that- do I have that option?
Entrance lens: 219 & 502 are OK but 69 looks jagged
Ion focus: looks like crap- all jagged.

Does this help?
I've put sources together for 10 years, I know to not let the leads touch the source body. The orance and blue wires are hooked up properly. What am I overlooking?
Thanks for your insight.