GCMS VOC mass 91 problems

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

7 posts Page 1 of 1
Hi Guys

I have a OI analytical purge and trap connected to a trace ultra gc and DSQII mass spec.

We have developed a problem with failed QC results and it appears to only really effect mass 91. Unfortunately for us this mass is used for quite a few compounds for quantitation.

The ion source has been cleaned, the column trimmed and everything else i can think off. We have had problems with the instrument since coming back after the xmas holiday 6 months ago. Since then just about every part has been replaced with new including the heated transfer line. There are also no obvious leaks according to the air water spectrum or using the helium detector.

Could this issue that seems to only effect mass 91 mean i just need to do more cleaning. I am kind of hoping this is something someone has seen before.

any suggestions would be most welcome.

thanks

Rory
Have you analyzed any samples with super high toluene levels in them?

I had an older OI purge and trap about 20 years ago and something in the valve would hold on to toluene when a really high sample went through it, and mass 91 should be the main one for that.

Is 91 present if you scan the instrument in tune mode without the tune gas present?

If so, remove the column and cap the inlet then try again and see if it goes away, if it does then it is a contamination within the purge and trap or gc. If it is the purge and trap or gc, then disconnect the transfer line and connect to helium so that you get carrier and bypass the purge and trap, that will let you know if the gc or purge and trap is the problem.

If you suspect the purge and trap, you can clean the sample pathway some by purging methanol instead of water and baking the system. An old Tekmar 2000 I had we would have to attach a 5ml syringe to the port where the trap connects and backflush the system to remove such contamination, but not sure you can do that on the OI.
The past is there to guide us into the future, not to dwell in.
Hi

Thanks for the reply. We have had samples with higher than normal toluene but not super high (80ug/l). Also we were having trouble with this mass before we had the high toluene samples. Having said that I will check back on all the samples this year to see if we have missed anything.

Im not sure what you mean by scan in tune mode ( i am still relatively new to this) but if I turn the filament on and scan between 10 and 100 to check the air water spectrum there is nothing at mass 90. Also if i open up the raw data file for a blank there is nothing of note on the spectrum except the 4 peaks for the internal standard.

I will try the things you have suggested.

thanks again.

Rory
Ropeypat wrote:
Hi

Thanks for the reply. We have had samples with higher than normal toluene but not super high (80ug/l). Also we were having trouble with this mass before we had the high toluene samples. Having said that I will check back on all the samples this year to see if we have missed anything.

Im not sure what you mean by scan in tune mode ( i am still relatively new to this) but if I turn the filament on and scan between 10 and 100 to check the air water spectrum there is nothing at mass 90. Also if i open up the raw data file for a blank there is nothing of note on the spectrum except the 4 peaks for the internal standard.

I will try the things you have suggested.

thanks again.

Rory


Turning on the filament and scanning is what we do with Agilent mass specs in what is called the manual tune mode, but you are doing the same thing when looking for air and water, just different software definitions.

Just wondering, when the source was cleaned, what solvents were used in the final rinses?
The past is there to guide us into the future, not to dwell in.
Hi, we clean with aluminium oxide and then ultra sonic bath with demineralised water and then methanol. We then put it in the oven for a bit to dry it out. The source was cleaned about a week ago. Troubleshooting gcms problems can be quite frustrating at times :)
Ropeypat wrote:
Hi, we clean with aluminium oxide and then ultra sonic bath with demineralised water and then methanol. We then put it in the oven for a bit to dry it out. The source was cleaned about a week ago. Troubleshooting gcms problems can be quite frustrating at times :)


Very true!

Just wanted to check and make sure no toluene was used in cleaning. You clean the same way that I do, so that eliminates the MS as the problem.
The past is there to guide us into the future, not to dwell in.
You did not note if you had done any maintenance on the purge & trap. If you have not, you may want to consider changing the trap and rinsing the sample path.
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