High bleed and noise

Discussions about GC and other "gas phase" separation techniques.

4 posts Page 1 of 1
Hy!

I've got a problem with high noise and extremely high bleed on my Agilent GC 6893- MS 5973 N (diffusion pump) system. Recently, the electron multiplier and filaments are changed and the whole MS system is cleaned. I use ZB-WAX (60 meters x 0.25 mm x 0.50 μm) column with the following temperature program 40 C for 5 min and then temperature rise with the rate of 2 C/min up to 240 C. The column is also brand new and installed by an expert.
What can I do to minimize the column bleed?

There is a chromatogram obtained for mix of standards in concentration of 1 mg/L : https://www.flickr.com/photos/162987565@N07/

Tnx in advance.
The bleed (baseline rise) is likely due to your new column. Even though they are much better now, they still bleed more than 1 or 5 phase columns. That will likely get better with time.

The grass noise is a different problem. The most likely causes are the HED or the electron multiplier horn. If you go to the Agilent website, you can find documentation that describes how to clean the HED (perhaps the EM horn too). If that doesn't work, it's likely that one or both are failing. I'm in a similar boat with a 5973N that's been in service since 2000. Turbo pump failed over Christmas break. After replacement, noise was high. Did some diagnostics and it appeared that the HED was the problem. Cleaned it and it got better but it's still not like it was before the turbo pump failure. I fear it's just old. 18 years is a long time! Might have to buck up for a new HED and horn to keep it going. Can't buy a new instrument for that!!!
How is your autotune like?

If that high bleed doesn't decrease after a couple of injections, it's possible you have too much oxygen in the system.
Autotune is very good. The values are almost the same as that of the first autotune when the MS was just installed in our lab. I suspect that maybe the problem is in the golden seal because it wasn't changed in a past few years.
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