Headspace transferline to Gerstel PTV inlet septumless head

[Søren Olsen]

Dear All,

For my master project at Copenhagen University I am profiling the terpene make up of industriel hemp. For that I am using an Agilent Headspace sampler (7694) in G1289 mode with carrier flow controlled by the GC (Agilent 6890N) and the vial pressure controlled manually by a pressure regulator. This configuration is due to software incompatibilities between the HS software and the Chemstation in using (D 03.00.611).

To capture the terpenes for the sake of focusing them on the inlet liner I am using a Gerstel PTV inlet (Cooled Injection System). This specific inlet I was able to use has the septumless head.

I have coupled the transfer line from the Headspace sampler to the GC by attaching it to the carrier gas supply nozzle on the septumless head. It is therefor not a needle going into the inlet head.

Can anyone with knowledge on these Gerstel septumless heads tell me if this way makes sense. How does it then work if I want to purge the inlet or use split injection? Is it possible? I'm having trouble getting satisfactory relative standard deviations on a Limonene 1% test solution I am currently using for trial-and-error approach.

I hope someone with experience can make sense of what I'm trying to explain.

Sincerely, Søren

[James_Ball]

I have not used the Gerstel inlet but I have setup such connections between an Agilent split/splitless inlet and purge and trap which is a similar setup. I cut the line going to the inlet and use it as the input to the purge and trap(headspace in your setup) then the transfer line from the purge and trap back to the inlet where the normal gas line would have been. You have to be sure to insulate any exposed tubing between the heated transfer line and the inlet so you don't have problems with condensation of analytes before the inlet, but otherwise it is a good setup.

The only problem I had with a newer GC was the electronic pressure control had trouble regulating the pressure when trying to do splitless or pressure pulsed injections. With the extra volume of the line, the response between when the controller increases flow and when it registers after the inlet causes it to overshoot and undershoot the pressure as it tries to react faster than the pressure change can get to the sensors. In split mode I didn't have much trouble with it and could run both a needle injected or purge sample with no problems. For splitless and pressure pulsed needle injections I had to simply reconnect the line as it was originally, bypassing the purge and trap. Easy to change that connection when needed.