Agilent GC-FPD (6890 N) signal and baseline problems.

[AGS QC Lab]

Hi all,

I'm new to the GC world. I have a Agilent GC-FPD (6890 N) with 60/80 Chromosil 310 column, Air and Hydrogen gas as fuel, Nitrogen gas as makeup gas and Helium gas as carrier.

I'm facing some problems and hope to get suggestion and opinions from this forum.

1. The signal output is dramatically different. Previous the signal output was around 7.0. The next day I switched on the GC, the signal output was around 890.0.

2. After I changed Hydrogen gas (as it finished), the baseline was behaved unexpected. The baseline was stable and the 20ppm SO2 peak as per attached . After few runs, I got a chromatogram as per attached and the baseline started unstable.

3. Hence, I decided to change another cylinder of hydrogen gas. The signal output was increased to around 1166. It looks stable but my 20ppm SO2 peak was not appear.

May I know what cause these problems and how should I solve it ? Any suggestion is highly appreciated.

Thank you very much.

[AICMM]

You don't seem to have a peak at all. To explain - your peak is stepping. While that can be a function of too low a signal rate, with a packed column that would be difficult since the peak will be broader to begin with.

How are you doing your injection? Gas sampling valve, syringe, other...?

What is the signal you get when you are trying to light the FPD? At the moment, the 1186 makes me think your detector is lit and you signal is making me think you are not lit. Are you generating a lot of water while the detector is running since an FPD will generate significant water.

It would be good as well to know what your detector flow rates are since these are critical in sulfur mode.

Best regards,
AICMM

[Peter Apps]

What is the source and purity of the hydrogen ?

Peter

[AGS QC Lab]

Thank you for your reply. My injection via gas sampling valve.

I managed to detect the issue was related to purity of Hydrogen used.

However, I still facing the baseline issue. The signal increased significantly (up to 7000) and fall back down.
The GC shown me the different output every time I switch it on. I did check there was water vapors from the exhaust. Thus, I think the detector was lit.

Moreover, I didn't notice that there were significant water generated while detector is running.

The flowrates I use are as below:
Hydrogen - 60 mL/min
Air - 60 mL/min
Nitrogen (makeup gas)- 30mL/min
Helium - 80psi

Thank you very much and have a nice day.

Best regards,

Vanessa

[AGS QC Lab]

What is the source and purity of the hydrogen ?

Peter

Thank you for your reply.

I managed to detect the issue was related to purity of Hydrogen used.

Supplier claims that the purity of the hydrogen was 99.999%.

Thank you very much and have a nice day.

Best regard,

Vanessa

[AGS QC Lab]

You don't seem to have a peak at all. To explain - your peak is stepping. While that can be a function of too low a signal rate, with a packed column that would be difficult since the peak will be broader to begin with.

How are you doing your injection? Gas sampling valve, syringe, other...?

What is the signal you get when you are trying to light the FPD? At the moment, the 1186 makes me think your detector is lit and you signal is making me think you are not lit. Are you generating a lot of water while the detector is running since an FPD will generate significant water.

It would be good as well to know what your detector flow rates are since these are critical in sulfur mode.

Best regards,
AICMM

Thank you for your reply. My injection via gas sampling valve.

I managed to detect the issue was related to purity of Hydrogen used.

However, I still facing the baseline issue. The signal increased significantly (up to 7000) and fall back down.
The GC shown me the different output every time I switch it on. I did check there was water vapors from the exhaust. Thus, I think the detector was lit.

Moreover, I didn't notice that there were significant water generated while detector is running.

The flowrates I use are as below:
Hydrogen - 60 mL/min
Air - 60 mL/min
Nitrogen (makeup gas)- 30mL/min
Helium - 80psi

Thank you very much and have a nice day.

Best regards,

Vanessa