Chromatography Forum

I am running VOC analysis on a 7697A Headspace/7890A GC/5975C MSD (all
Agilent). I have been getting a slight rise in baseline. It is
temperature dependent but levels off. The DB-624 column is rated for
260C and I have my max set at 180C. If I run it at a higher max temp the rise is
more exaggerated but again levels off. Any recommendations to stabilizing the baseline?

https://drive.google.com/file/d/0B7ZnVv ... sp=sharing

Welcome to the forum.

That baseline rise is VERY slight, and compared to the size of the peaks I doubt that it will have any effect on integration. The short term noise would bother me more.

Peter

Thanks for the response!

The system ran with an inlet leak and an old column for quite some time before I got my hands on it. The noise was worse before but has continually improved. As long as I have definitive peaks is it really something to be concerned about?

Wendy

Hi Wendy

Baseline noise makes peak integration less repeatable. As long as you are happy with the repeatability of peak areas then the noise is not a problem.

Presuming that you are using an FID it might be worth cleaning the jet and collector if you have not done that already.

Peter

Hello

If you're using FID I wouldn't worry about baseline drift - it is quite low and you can easily integrate all peaks.
However if you'd like to improve your chromatogram you can use option: column compensation - blank run will be subtracted from your normal run (of course you need to run blank first and then set it up in method).

If it is MSD perhaps column DB 624ms would be better as it is low-bleed column.

Regards

Tomasz Kubowicz

I am running VOC analysis on a 7697A Headspace/7890A GC/5975C MSD (all
Agilent). I have been getting a slight rise in baseline. It is
temperature dependent but levels off. The DB-624 column is rated for
260C and I have my max set at 180C. If I run it at a higher max temp the rise is
more exaggerated but again levels off. Any recommendations to stabilizing the baseline?

https://drive.google.com/file/d/0B7ZnVv ... sp=sharing

Since you are using the 5975MSD you need to look at the individual quantitation ions and not the total ion baseline rise. If you are not seeing interference with the quant ions then there should be no problem.

If you look at the spectra for the higher baseline you will probably see mostly m/z 207, which comes from the column phase bleeding off and is normal and will rise as column temperature rises. As Tomasz said, you can get less bleed if you use a 624ms column as they are made to have lower bleed, and one I am using now is the Restek Rxi-624-SilMS which has an upper temperature range of 310C which helps give even lower bleed at your current max of 180C.

If the background spectra shows m/z 44 as the bleed rises then you are having a leak and the rise is caused by CO2 leaking into the instrument, which usually means a cracked ferrule or column or bad septa, but your chromatogram does look more like just normal column bleed.

M/z 44 can come from water samples as well. We have a leak tight system and see 44 while the "water peak " is eluting doing P&T.

Thanks for all the feedback! I actually just ordered the Rxi-624-SilMS but I had this Agilent column on hand and wanted to make use of it.