Chromatography Forum

Dear all,

I was involved in some trace analyses in which the peak I am looking at is small and close to others much larger. However, I was able to see traces reasonably well.

Suddenly I had a septum leak and I replaced it. However, I did not realise the leak until the second injection. During the first injection after the leak I saw no peaks, while the temperature program went on.
In the second injection, I saw very few peaks, with a lot of tailing and shifted retention times, which led me to think immediately about the leak.
There was no head pressure in the gauge.

Nevertheless, once the septum was replaced and the pressure back on, the column had lost resolution. The small peaks were not as defined as before and all the others had widened enough to cover a considerable proportion of my target trace peak.

At the beginning I thought it was just a superposition of my pattern and septum bleed what caused the peaks to increase its width and overlap my trace peak. This is not the case, as the blank gives a perfectly fine baseline and I have cleaned and conditioned the septum as well to rule out such possibility.

I suspect that, during the first injection after the leak, the temperature program went on and there was no gas going through. This could have caused the column to degrade and, therefore, lose resolution.

What are your thoughts about this?

Regards

Depends on the type of column, how long it was at an elevated temperature, and the temperature involved. And, if your septum failed suddenly, it was probably leaking seriously before it failed - splitting some of the sample out into the room. You can try injecting less material to see if large borad peaks take on a better shape. If it is an issue of loading, you are lucky.

While the resolution is decreased, how about the retention time and peak area? do these parameters change? and how?

The column is a CP-SIL 5 CB 100 % dimethylpolysiloxane.

The column reached 240 ºC for 15 min without gas going through.

The retention time does not change, only the resolution. I see exactly the same but less resolved.

Small peaks are not as well resolved as before and the area of peaks close to larger ones is smaller due to overlapping.

Can you post pictures of chromatograms before and after? (Same sample preferably)

Check that you do not have a fragment of septum in the inlet liner.

Peter