Chromatography Forum

Hi All,

You see. ON SIM or TIC, the abundance is never negative. So then, the software will cut off the negative part of the signal as you see on the above picture. This situation can lead to incorrect intergration of peak. I don't know why. I have already changed the threshold value, but it didn't work. Pls, give me an experience advice.
Thank a lot.

It is not possible to have a negative abundance value in mass spec. A mass spec signal is absolute and therefore cannot be negative. It is not relative to some baseline like with UV or FID detection. You may have an apparent negative value if you are subtracting background. Also, I see no reason why the chromatogram that you posted cannot be integrated properly if you have the integration settings set up the right way.

minhtruc,

When you say your integration is incorrect, what exactly do you mean? I think your bigger problem is that your ions are down in the noise (evidenced by the spectrum) and thus are going to be hard to differentiate. I've seen lots of peaks that looked like this at the low end of the curve and without significant integration issues. However, you say the same thing happens in SIM? This should be a much cleaner peak.

By the way, how much of this component did you put on column?

Best regards.

I take away a curiosity?
that version of chemstation is yours?