Column installation problem

[atiqah_ms]

Dear All,
Good day..

I am newbies in GC world and have few doubts. Really hope for guidance from you all. Thanks.


Actually I've by GC column DB-5 (30m x 0.32mm x 0.5um) and I have try to install the column according to the procedure as below :
1.Column installation (Done-OK)
2. Leak and installation check
3. Column conditioning
4. Setting linear velocity / flow rate
5. Bleed profile
6. Test mix

However I am stuck at 2nd step.
I've try on direct inject of non retained compound (source:lighter) and there is no peak obtained

The test condition used as below:

GC instrument: PE 1100 autosystem
Carrier gas: Nitrogen
Liner: Wide bore liner
Mode: Split
Carrier gas pressure: Ive try with: 1) 2.6psi // split vent: 85.6ml/min, 2) 6.2 psi// split vent: 180ml/min, 3) 25.0 psi// split vent: 444ml/min
Oven temperature: 150 oC (isothermal)
Injector: 250 oC
Detector: FID (300 oC)
Running time: 30 mins
Carrir gas set at tank: 90 psi

Compared to condition as column performance cert.

Inlet: 250 oC split at 75 ml/min
Detector: FID (320oC)
Carrier gas: Hydrogen
Flow: 38.8 cm/sec (1.9 ml/min)
Hold up time compound: methane (1.288min)
temperature program: Isothermal at 150 oC

My questions are:
a) the split mention as per cert was 75ml/min , How to check the figure? Does the figure come from the detector or split vent using flow meter?
b) Does my split ratio was to small and all sample was vent out?
c) According to the Van deemter curve, N2 diffusion was lower than H2 and He. Do I need to double the figure of split or any parameter as mention on cert cause using N2 as carrier gas?
d) Could anyone suggest on the method for non retained compound using N2 as carrier gas?


Thank you.
Sofia Atiqah

[Peter Apps]

Hello Sofia

If you have not already done so; remove the column from the detector and dip the end into some clean solvent - if you can see bubbles it confirms that you actually have carrier gas flow through the column. If you see bubbles, re-install the column to the detector.

How much lighter gas are you injecting ?, and how are you doing the injection, manually ?, autosampler ?

How are you monitoring the signal from the FID ? - if you are looking at a chromatogram on a computer monitor do you see a dead flat line ? What happens if you zoom in on the baseline until you can see small fluctuations, can you see the gas peak then ? Can you get a value for signal output on the front panel of the GC ?, does it change when you inject gas ? Does the signal, or the line on the screen change if you turn off the hydrogen to the FID ?

Hold a cold shiny object, like a spanner just above the outlet of the FID - if you see condensation it means that the FID is flame is burning. No condensation means a detector problem which would account for the lack of response.

Peter