Chromatography Forum

Hi
good morning!

I have a question regarding the use of Fast GC column 20m 0.18mm 1 um for residual analysis by using head space. During operation conditions of GC high GC inlet pressure was obsereved. Can I use Head space at that high temperatures?

Thanks,
Srinivas

About which are you asking? high pressure or high temperatures?

Hi Rodney,

Sorry its typo error, head space operationg at high pressures??

Thanks
Srinivas

It depends upon the volatility of the chemical you seek to measure. It will tend to return to the liquid phase and lose equilibration when you pressurize the vial at high pressure. This will tend to give you inconsistent results unless you give adequate time to achieve equilibration, which if you do, you will tend to lose the partition (no peak) of the analyte.

You might wish to shorten the column and use a .32 or .53mm ID precolumn to assist in getting a suitable split.

(just a suggestion)

Rod

With a loop type headspace injector plumbed to switch the loop into the carrier gas flow the inlet pressure should make no difference - the loop is still filled by bleeding excess pressure in the vial down to atmospheric. I would be wary of syringe injections against a high inlet pressure.

Peter

High inlet pressures of column and gas samples are always a challenge as not everything will leave the needle causing increase of RSD.

Loop injection is much better.

Other thing to be aware of is that 0.18mm need sufficient splitting to make teh volatiles elute as reasonablke peaks. Most headspace application look bad because of injection peak broadening. Thats also where larger column ID makes life easier..
I would use a larger (0.32mm)diameter and use flow and temp. programming(with FID) to reduce the run time

jaap
Restek corporation