Chromatography Forum

Hi all I have started running my Tekmar 7000 today.

I am trying to use a pulsed split injection to minimize the split necessary. I set it up for a 3:1 split at 30 psi for 1 minute. That translates to 3 ml/min column flow 12ml/min total down the transferline. The trouble is it seems like the Tekmar 7000 doesn't tell the GC to go to prep run. It takes a minute for the EPC to generate the appropriate split and pressure. However, It goes right from standby (1 ml/min column gas saver) to inject/start. I ran a few injections by manually hitting prep run and it looks good but the 7000 gripes about constant heat time violations.

I have injection source set to manual inject. What is the difference between manual inject and external device in Chemstation MSD? Finally how can I program the pulsed split so the GC EPC has time to generate the appropriate values before inject.

Hello

1. I think it will be always problem (pulsed splitless with Tekmar transfer line in GC flowpath-EPC won't be able to cope with it). I'd recommend straight liner 140ul for gas samples and split mode.
2. If you have manual injection mode you need to press start button to run GC. With external device mode, your external device (eg. Tekmar sampler) sends signal to start run. Of course you need remote cable between sampler and GC/MSD

Regards

Tomasz Kubowicz

I thought about it a bit last night and I am thinking I can set the inlet parameters to the pressure pulse settings then in Chemstation under column flow I can set it to 1 ml/min at 1 minute into the GC run and keep the gas saver off. That way at the beginning of the run it is all set for the pressure pulse when the Tekmar injects and 1 minute in it can switch to normal GC operating conditions.

I don't think it is so much the Tekmar as the 6890 EPC has trouble doing low splits. The back inlet takes a minute as well to generate a pulsed split and it has nothing hooked up to it.

Yes - I do not believe the inlet was designed to do these low splits - our lab does it a lot, and a tiny leak that would otherwise go undetected will show up, particularly when trying a pulse.

The inlet expects a minimum flow of 20 ml/min. Anything below that is a crap shoot. It is a crap shoot that often 'works', but it is not designed to.

Is the GC configured to Auto Prep run On? Would increasing the GC Cycle time in the 7000 software help?

Thanks I didn't know there was an autoprep run. That solves my problem.

actutally enabling the autopreprun doesn't send the ready signal to the 7000.

Therefore the solution is to set the injection parameters in Chemstation to the pulse parameters and under column flow choose ramped flow and set it to whatever the normal flow after 1 min then hold for the rest of the run and disable the gas saver.