Running TPHg and TPHd on Varian cp 3900

[jeff sch]

Hello:

We ususally run TPHd on our 3900 which has a Varian FactorFour VF-1ms 15 mm, 0.25mm 0.25 um column.
It is fed by a 8400 autosampler (Varian), with a 1177 injector @250 C. Column oven program is set at 50 C to hold for 2 min then ramp to 250 C at 20 C/ min. The total run time is 20 min. The FID temp is set at 250.

My problem is we are trying to develop a method for TPHg on this same machine/column. I have tried playing with the different parameters by adjusting column flow from 1 ml/min to 0.5 ml/min, lowering temperatures for the injector, slowing the ramp program to start at 35 C and ramp to 235 C at 10 C/min. It appears that my gasoline stuff is blowing through in one clump at two to five minutes no matter what I do.

Normally we run TPHg on a 3800 via purge and trap using a Varian Crompack CP-select 624CB column, 30m, 0.53mm.

I do not know much about these specific columns, but I am starting to think that the 15m FactorFour is not real good for seperating gasoline range hydrocarbons. If anyone could help me with some ideas to develop a methos with that column on the 3900 I would appreciate it.

Thank you,

jeff

[chromatographer1]

Jeff,

You have a short thin film MS type column. You should not be surprised that c3-c8 hydrocarbons elute quickly.

Your 624 column which you did not state the film thickness, is it 3um ?

High resolution hydrocarbon analysis is performed on 60 to 100 meter MS columns, usually 0.25 to 0.5 um film thickness.

To separate HC which have SO MANY components you are required to have plates plates plates, unless you wish to do class separations.

You could try using subambient oven temperatures to use the short Factor Four column like -10 C and then SLOWLY ramping the oven.

OR

Get the right column to do the job you need.

Good luck,

Rod