Chromatography Forum

Hello all!

I am currently battling an extremely noisy basline on a Purge and Trap 7890/5975 system used for 524.2 VOCs right now. I've really tried everything i know of (threshold, sample/scan, tuning, etc). Furthermore, the HED has already been replace (although, its hard to imagine that it was needed in a 1 year old instrument). I was just wondering what anyone had to say about the issue.

I have been running direct injects for about a week. All of them look better than purged samples (next step of troubleshooting is the concentrator), but still have a very noisy baseline.

An Agelint service tech came out yesterday and told me that it was all how it was set up. He made it sound like it was human error or lack of knowledge that is the problem... However, i just started at this lab last week, but i am anything but a novice when it comes to working on and setting up Agelint GC/MS systems....

Any thoughts? Thing that you have changed in your system to clean up a noisy baseline?

Thanks!!

Okay, so last night i replaced the HED and EM... However, there is still well over 300 peaks found in the Atune... I do have an instrument in the "graveyard" so i am going to attempt to put that in despite the concern of oxidization... Either way, i think that we are going to get PTS out here to service the instrument and at least attempt to get it running...

Any suggestion yet?

Hopefully, i will have this figured out soon and i will post whatever findings that i have.

So you have a noisy baseline during data collection, and you have a lot of peaks during an autotune? I suppose the simplest solution would be to remove the column and cap the detector...see if that helps the tune.

And by direct injection of samples..what do you mean? How much matrix is being introduced into the system for each run?

Yes, that is correct. I have an elevated and noisy baseline. I'm thinking that this is due to the 410+ peaks found in Atune's, BFB tunes, and manual tuning...

i have already capped the detector and had no drop in the number of peaks in the MS.

By direct inject i mean that i directly injected standard into the injection port and seperated the GC/MS system from the concentrator. I am not really introducing "matrix" onto the instrument.

You say that you capped of the detector and still have many peaks in the MS. If the MS is capped off, the only peaks you should see are those from PFTBA on tuning. If you are seeing more than that, they are coming from somewhere -- and that can only be contamination.

If you capped off the detector by using a blank ferule on the transfer line, I would suggest either cleaning the transfer line or, if you have a blank flange, put a blank flange in place of the transfer line and try again.

This could be something as simple as some part of the source or the end of the transfer line was touched with fingers and fatty acids are cooking off. (Why do I always wind up cleaning a source after having pizza for lunch? Side issue...)

I wish you luck.

Like Don mentions, you probably have contamination on the source. In addition, without opening up or venting the system, you can do a couple other tests:

1-Switch filaments in the tune settings, to see if that changes anything (the filament you are using might be shot, but this is unlikely to produce many ions like you are seeing.)

2-Bump up the source and quad temps to the max for a while, to see if this helps with "burning out" some of the contamination.

Call your Agilent service rep back and explain to him your problem with the MS capped off. It eliminates his argument about "how it is set up" since you have already done half of his job and isolated the problem to the MS. If you hear a bit of frustration in this post it is because I had the same argument long, long ago with a service rep who did exactly the same thing... Very frustrating process.

The other thing is, can you post a spectrum scan from the capped off MS? Better if you can post one with and one without the PFTBA valve on. Might help us elucidate possible source of the noise.

Best regards.

It seems that after a little elbow grease (in cleaning the source and generally wiping things down) and the very handy MS bake out (thanks Schmitty) we have fixed that problem. I am still a little unhappy with the noise in the baseline, but i think that most of that was due to scan/method setup. Like i said before, i think, last week was my second week here and i was almost entirely unaware of how this instrument was run (excpet for the maintnance log).

I am still having the same problem on the 6890/5973 system. Can you believe that 2 systems in the same room are having the same problem?! I havent actually, in over 5 years (yes, i am a pup) of experience, seen this. Yet, there are 2 in the same room, at a drinking water lab that suffer from this!!

Anyway, i will follow the same course of action to attempt to solve the other. If i come up with something else, i will repost.

okay, so i cant figure out how to add an print screen image to the posts.... other forums that i'm on allow attchments... i guess that this one does not?

Use the image tags (Img and /Img) when you make a post. The button is right up there ^^^. You must first host your picture online. I use imageshack. The should be instructions around here somewhere too, maybe in the HPLC forum...?

I guess you have done the source cleaning. So, my idea is to turn off the heater of the transfer line. If the noise peaks come from that, they will then go off.

I guess you have done the source cleaning. So, my idea is to turn off the heater of the transfer line. If the noise peaks come from that, they will then go off.

that is a good suggestion, but i have already capped the MS from the rest of the system and still had the problem. I have a service tech from PTS coming out here today or tomorrow, so i will post whatever we find after that...

Fed by the same gas supply by any chance?

Best regards.

I guess you have done the source cleaning. So, my idea is to turn off the heater of the transfer line. If the noise peaks come from that, they will then go off.

that is a good suggestion, but i have already capped the MS from the rest of the system and still had the problem. I have a service tech from PTS coming out here today or tomorrow, so i will post whatever we find after that...

Even though, the ghost peaks could still come from the transfer line itself, you may need to clean the part thoroughly.