5973 Loses sensitivity

[a2j812]

Sorry if I'm reposting on the same topic, but I searched and didn't find anything relevant to this problem. And let me apologize for the War and Peace sized post.

I am running a OI analytical 4552 autosampler with a OI Eclipse 4660, connected to an Agilent 6890/5973 GC/MS. Standard 8260 soil method.

about 2 months ago, I ran a sample with LARGE amounts of 1,1,1-TCE. After running literally about 1000 blanks and changing the entire sample pathway, I had the source cleaned the electron multiplier changed and the column replace as well and the inlet sleeve gold seal, etc... You get the picture. Ever since this work was done, I am having one heck of a time attempting to tune this MS. No matter what I try I cannot get 219 above 131 with my ratios where I want them. Once I get it tuned to the point where I can get BFB to pass it will hold that tune for about 12 hours and then it's a struggle to get a BFB to pass and I'm losing sensitivity as well. For example, Pentafluorobenzene starts with a response of 301951 and 24 hours later I'm getting it responding at 58011.

There is no leak in the autosampler or the concentrator. Ferrules are tight on the column and the gold seal and septa are new and installed properly. I would appreciate any help anybody could offer on this.

Thanks.

[AICMM]

a2j812,

Is it maintaining a tune if you do not run anything? Can you walk up 12 hours later and get the same tune after a few minutes of warm up?

Perhaps you need to dip the quads? I have done this on 70's, 71's and 72's but admit never done it on a 73.

Also, what are the flow rates going into the GC?

Are you purging BFB or direct injecting BFB? Is you instrument configured with the splitless/split inlet?

Best regards.

[a2j812]

I don't know of the tune will stay put if I leave it. I haven't had the opportunity to let it sit idle that long. The flow rate is 1mL/min and it is running in split mode. I'm thinking that there may be a small leak in the MS. I can see 44 in the baseline but it isn't excessively high, and it remains constant through the scan and through the entire sequence.

[danicrd]

Hi a2j812
I thought to be the only one with similar problem...
Anyway: I have same sistem, and same problem!
The sensitivity drop down during analytical batch.
The only workaround i have found is source cleaning. The system is stable for 2/3 weeks, depending on sample: before this time area starts to decrease during batch.
Is your source clean? Doesn't matter, clean it again.
Another problem can be EM saturation: watch to your method offset. High EM offset lead to Em/HED saturation.
Try to look this agilent bulletin F05013.

Good luck!

[danicrd]

Hello
have you fixed the problem?
I'm very curios to know...
Thank you

[a2j812]

It seems to have worked itself out for the most part. It has been holding its tune now for about a week and my internal standard responses are 2 to 4 times higher than they were when the problem was at its worst. There is a bit more fluctuation in the responses than I like to see and as soon as I get the chance I'll have the source cleaned again and seal the MS up really well with some grease since I think part of the problem was a leak. Sad to say that I don't really know what was done to help fix the problem. Sorry I cant be more help.