Chromatography Forum

Hello,

I am improving my Headspace -GC - FID method for analysis of terpenes. I am struggling with carry over in between runs. I am using the Tekmar HT3 headspace instrument with the following parameters:

Valve oven temp: 160 C
Transfer line temp: 170 C
Standby flow rate: 50 mL/min
Platen/sample temp: 180 C
Platen temp equil time: 0.00 min
Sample equil time: 0.00 min
Mixer: on
Mixing: Level 5
Mixing time: 10.00 min
Mixer stabilize time: 0.00 min
Pressurize: 9 Psig
Pressurize time: 0.50 min
Pressurize equil time: 0.25 min
Loop fill pressure: 9 Psig
Loop fill time: 0.25 min
Inject time: 1.00 min

I have been injecting a Restek Terpene standard mix #1 usinh methanol as the diluent at a concentration of 120 ppm. I have seen a method which uses this headspace unit using headspace-loop split injection at a split ratio of 10:1 but haven't found this parameter when editing the method.

Please let me know if you have any suggestions or ideas.

Thanks,

Taylor

What size is your loop? How do you have the transfer line connected to the GC? I prefer to put them in series with the GC inlet's gas supply. The split ratio should be in the GC's inlet parameters.
You could use a smaller loop instead of splitting.
Carry over can be addressed by either increasing the standby time.

Hello,

The loop size is 1 mL. The transfer line is connected in parallel with the carrier gas, so I could try to connect them in series.

Thanks so much for your help!

Taylor

If what you have written is correct, you are heating your vial hotter than your sample loop or transfer line. Reduce the platen to 150C

Vial temp is 180C - "Platen/sample temp: 180 C" ;
Loop temperature is "Valve oven temp: 160 C";
Transfer line is "Transfer line temp: 170 C"

Dave

Thanks Dave. I will go ahead and reduce the platen temp to 150 to see if that helps. I appreciate your feedback!

Taylor