Chromatography Forum

Hi

We bought a 60/80 Carboxen-1000, 15'x 1/8" (2.1mm ID) column for the analysis of N2, O2, CO and CO2. I installed the column and conditioned it overnight at 225°C. After conditioning I did a blank run following the recommended temperature programme. In this blank run there was a huge peak at approx 12-13 min. I am working on a HP5890 with TCD detector. Since the initial blank run, I have cleaned the injector, replaced the oxygen trap, cleaned the moisture/molsieve trap on the He carrier gas line, but with no luck, the blank run still has the big peak. I have not injected anything on the column yet.

Please help. Is this a column problem or is there something wrong with my system? I cannot think of any other system maintenance that may solve the problem.

What is the peak like? Is it narrow/gaussian with a large rise in signal or is it a huge spread out hump during the temperature ramp?

Hi, it is a relatively narrow peak with large rise in signal, tailing present. It is definitely not a spread out hump. Supplier says it is a water peak, but it was there directly after conditioning.

Hanlie,

Did you make an injection? If not, I can't see how it is water considering your conditioning. Many people do not take water into account when they run samples but you still have to run something to see it after cooking the column. By the way, water typically has a very ugly peak shape....

Best regards.

Hi

I am still struggling with this peak. Initially I did not injected anything onto the column. After recommendations from the supplier, I injected water onto the column and it has a similar retention time as the unknown peak. After injecting water I have done a lot of blank temperature cycles. The peak is still present, but has changed shape since. Before it was a nicely shaped peak, now it is an ugly shaped, tailing peak - as you said water would be. Assuming it is moisture, I still cannot determine what is causing the problem. I also do not understand why it is not disappearing after a few temperature cycles.

The water is in the carrier gas. After a GC run, oven cools down to initial oven temperature. Water accumulates at the head of the column, it elutes during the next temperature ramp. To prove this, you can run blanks with different interval between them. The longer the interval between the blanks, the bigger the water peak. That being said, you don't need to worry about it because the fixed gases should come out way before the water peak.

With this specific column CO2 co-elutes with the water peak. Shouldn’t the moisture trap get rid of moisture in the carrier gas?

Hi Hanlie

Your posted that you cleaned the moisture trap - maybe it needs to be replaced instead.

Peter

Hi Peter

Thanks, I'll try.

Regards
H