Chromatography Forum

Hello,

I am analyzing gas samples for H2 composition with a HP 6890 GC in TCD. I used to get nice peaks (symmetric), just recently I started to see tailing in the peaks, and then it became even like a shoulder. I conditioned the column twice overnight but it did not solve the problem. The column I am using is a packed column Hayesep Q 80/100 and then I replaced the column with a brand new one. This reduced the peak tailing but there is still tailing and I could not figure out the reason. I changed the septa, and there is no liner. So what else can I do?

Another thing is that whenever I inject pure H2 of 250 uL volume there is tailing but when I inject 25 uL there is no tailing at all. I did not change anything in the method or my injection way, the syringe etc. I used to get good peaks with 250 uL injection with the same method. Do you have any suggestions?? What can be the reason?Thanks a lot.

My guess is you have voids in your column from the manufacturing packing.

I don't know your vendor but not all vendors pack equally well. I fixed one vendor's production problems when I worked there. I had to solve it for myself several years earlier when I used to pack my own columns and I discovered that the traditional methods usually produced voids, which cause tailing and distortions in the peak shape.

In fact, Supelco used to include a letter of (it not our fault for voids) with every porous polymer column. To a degree that was true but the real issue was the manufacturers of the porous polymer beads did not clean up their product as well as they used to do in days of old. Remedy to that problem was not quick but I did achieve packing methods that minimized the shrinkage of the polymer beads with time and heat.

Good luck in finding a good vendor and a good column.

Rodney George