biggest gap in GC column performance

[Wayne Way]

What are your thoughts on the biggest gap in GC column performance?

selectivity
bleed
others?

[Peter Apps]

Selectivity ? meaningful only in relation to separating specified sets of compounds. Give me a selection of column pairs and a Dean's switch heartcutter and I'll separate any two compounds you care to name.

Bleed ?, as long as the carrier gas is clean and the samples are not wet or aggressively reactive, modern bonded phases are very stable. with selective detectors bleed can often be ignored, and as long as it is consistent bleed can be subtracted by most software data packages.

After the FID the column is about the best performing part of any GC, now if someone could come up with a good inlet they would deserve a whole string of awards.

Peter

[gpronger]

The inlet is often the key for a lot of what we do so I agree with Peter with that response.

The one aspect we see in the environmental testing arena, is that though we have columns that can handle the separation (I am speaking mostly about pesticides now) is column robustness. The more polar columns that are often tailored for this application tend to have significant durability issues. Sure in a perfect world I we would be passing 100% of our samples through numerous cleanups, but the reality is that most are extracted, concentrated, and delivered to the instrument "As-Is", and only diluted or a clean-up applied after seeing the sample (sure we could be screening everything in the prep department, but the time factor is a strong barrier).


Greg

[Peter Apps]

Hi Greg

Do you think that deterioration with dirty samples is the column phase itself falling apart, or muck getting deposited ? If the latter a retention gap (which I see as being part of the inlet since it does not do any separating !) might help.

Peter

[Consumer Products Guy]

Agree: inlet condition

[gpronger]

Some of both, but if I were to hazard a guess its more the phase getting messed up than material deposited.

The reason I say this is that we run dual columns and we'll see one last significantly longer than the other and typically its the more polar that'll die first. If it was just stuff at the head of the column it should not be as much tied to one column. Depending upon the manufacturer, we may have the more polar of the pair of columns last 1/3 the life of a lesser polar column (2 - 3 months versus 4 - 9 months under).

Greg

[krickos]

Hi

Generally speaking I agree with Peters initial post.

However one can still for example run into column manufacturing differences.
Complete loss of signal/gross degradation of nona/deca brominated PBDEs is one example.
Loss of baseline separations of some residual solvents when doing pharmacopiea analysis with -624 type of columns is another.

[Don_Hilton]

Related to the issues above noted with polar columns - some of us have been waiting many years for a wax type column that would go to 350 degrees or more. It could be really helpful with some larger molecues.