Peak/noise before 2 min retention time

[Mariandrea]

I have observed a signal before the two minute retention time on the chromatograph. I am not sure if it is just noise, or if its marking the start of a new peak. But it looks like a negative small dash at a retention time of 1.8 minutes. My theory: GC detects a very small amount of Hydrogen but not enough to form the entire peak. Does this sound correct? Thanks!!

[dblux_]

I have observed a signal before the two minute retention time on the chromatograph. I am not sure if it is just noise, or if its marking the start of a new peak. But it looks like a negative small dash at a retention time of 1.8 minutes. My theory: GC detects a very small amount of Hydrogen but not enough to form the entire peak. Does this sound correct? Thanks!!

Is your detector sensitive to hydrogene ?
As a kind of homework try to correlate 1.8 minutes with time taken from injection to detector by carrier gas and unretained molecules.

[chromatographer1]

You are not giving enough information for anyone to give you an answer.

Please describe your sample, your injection propers, and your detector as a minimum amount of information if you really want an answer to your question, as I assume you do.

Negative peaks can be produced by many issues. At $1 per answer how many do you wish to buy?

best wishes,

Rod

[dblux_]

... At $1 per answer how many do you wish to buy?

Mariandrea, even no attempts to negotiate the price ?

[Don_Hilton]

Basic questions:

What kind of detector - detectors have differening sensitivities, some will never see hydrogen.

What type column, dimensions, carrier gas and flow rate?

What kind of sample? Are you injecting gas? Liquid? How much? and what are the inlet conditions. Any valving involved?

All of these make differences in what one will see in a chromatogram.

[palli87]

I have observed a signal before the two minute retention time on the chromatograph. I am not sure if it is just noise, or if its marking the start of a new peak. But it looks like a negative small dash at a retention time of 1.8 minutes. My theory: GC detects a very small amount of Hydrogen but not enough to form the entire peak. Does this sound correct? Thanks!!

Hi!

it could be an effect of turning valve of injection.

[chromatographer1]

Assuming you are using a TCD.

Again I complain , no info given.

A valve action usually gives a small INCREASE in the baseline, sometimes a sharp peak, but small.

Hydrogen, depending upon the carrier and the concentration CAN give a NEGATIVE peak.

best wishes,

Rod