Cut peaks on Agilent 6850

[Sylvain B]

Hello,

First I apologize for my english.
I'm using an Agilent 6850 GC with an AZUR data system. When we select the gain to +/- 1.25V in the data system, we observe our peaks are cut around 0.7 V.
We tried to change the gain to +/- 10V and then we get peaks which are cut at 7V !!
First we check the AZUR data system and connected the acquisition channel to another GC (Focus) : it's working perfectly. So it seems the problem comes from the 6850 GC.
Is somebody already experience this kind of problem ?

[Peter Apps]

Hi Sylvain

It will be very helpful if you could post a chomatogram - instructions are in a sticky at the top of the LC page.

Peter

[GasMan]

I assume that you are using the analog output at the rear of the GC, and when you say that the peaks are 'cut' at .7Volts, you mean that the peak has a flat top.

This is a sign that the 'range' setting for the GC is too low, you are overloading the amplifier. Try increasing the range setting so that the amplifier is not overloaded.

Gasman

[AICMM]

Actually, I am pretty sure your amplifier can handle more since the Agilent amplifier has a huge linear range when you run it with their data system. The issue is that your output cannot handle more, that is your peaks are bigger than 1 V. The solution is still the same, you have to change the range setting as per GasMan's suggestion. The thing I am curious about, though, is that the 0-1 V really does go to 1 volt so something is eating away at 300 mV of your signal. What is your baseline value right now?

Best regards,