Chromatography Forum

Has anybody had experience with these types of columns? Our last column was a metal column and it was very difficult to score and cut. I checked it with a 10x magnifier and the cut came out clean, but the column would come out all bent afterward. Well I found out today that for the new metal column we just bought (a varian ultimetal) needs a straightener and a tubing cutter. I wish I had known this with the first metal column we got (a restek mxt-tg), which died quickly after a cracked ferrule got air into the system at high temps (at least, that's what I think happened). Even though the tube cutter was expensive, it put my mind at ease b/c I know I'll be making a cleaner cut than scoring and breaking will.

But could it be that a bent or distorted shape of the column going into the inlet had anything to do with shortening our column's life? We basically spent $500 on a new metal column only to have it die on us before we could actually put it to use. I believe the root cause was using it with a cracked ferrule, but I could be wrong.

Usually only a very short piece of metal column is inserted into the inlet of a GC. If you were working on biodiesel samples then the column goes into a cold on-column injector and this curved or bent column end should not be a problem as it bends to conform to the inlet.

It sounds like you carrier gas is contaminated. Even if you have a trap to clean ppm amounts of air and water from your carrier gas a leak at the backside of the trap will give you grossly contaminated carrier gas to your GC. A leaking septa at the injection port will also allow air into the carrier.

I would condition your biodiesel column at 360°. That thin phase coating will lose all bleed from any manufacturing contamination readily. And remember that your column was conditioned when it was made. It may have a trace amount of phase breakdown to remove but normal use will take care of that after only a few runs.

Oxygen and high temperature equals phase distruction. The Restek and Varian columns you use are good columns and should last weeks if not months of continuous use. If they don't you are not doing something right and need to correct the fault.

Good luck and best wishes,

Rod

We've used a Quadrex metal capillary for years, no problems. I'm assuming you have a metal capillary because you planned on going to temperatures higher than fused-silica can handle, which means you likely don't have a PEG-type phase. So I'm not so sure the column is dead. Disconnect the column outlet and place in a beaker of solvent and look for bubbles to indicate flow, or measure the flow if you have a set-up. If so, re-install and try a microliter of solvent and see if you get a typical solvent peak, and if successful, go to something simple next. Baby steps. And make sure your detector is operational. Divide and conquer.

Disconnect the column outlet and place in a beaker of solvent and look for bubbles to indicate flow, or measure the flow if you have a set-up. If so, re-install and try a microliter of solvent and see if you get a typical solvent peak, and if successful, go to something simple next. Baby steps. And make sure your detector is operational. Divide and conquer.

That's part of our operational procedure during startup. We do get a signal whether we do a solvent blank or a methane test, but when we do a run with a solvent blank we get very high tailing and noise at the end. I've replaced the jet, I've cleaned all the detector parts, and the inlet parts; so I'm pretty sure it's the column. Could it be the column wasn't conditioned enough?

It sounds like you carrier gas is contaminated. Even if you have a trap to clean ppm amounts of air and water from your carrier gas a leak at the backside of the trap will give you grossly contaminated carrier gas to your GC.

I've leak checked the carrier gas around all the fittings, valves, and traps. The traps also show no sign of contamination and are still active.

leaking septa at the injection port will also allow air into the carrier

The unit will shut down if there's a considerable leak there. Although it takes some degree of pressure drop to activate that feature, I do leak check the inlet whenever I take it apart and put it back together. We replace the septa once a week on top of that.