Chromatography Forum

Hello,

I am working with a sample that I know is a single component 100 ppm toluene balance air mixture. The temperature profile is 150 degrees C isothermal, using a bonded C18 Chemipak column, run time is 4 minutes. Detector temperature is 225 C. Does anyone have any suggestions on how to improve the peak shape of this toluene? I am getting poor quantification as a result of this peak shape. I also get this sort of response with other higher alkanes, such as C6 or higher, but lower alkanes such as methane or propane give excellent, gaussian shapes peaks and repeatabilities of less than 0.2% of reading.

Thanks

Is carrier gas flow rate optimal for your column ?

What happens if you run the column hotter? The fact that the problem occurs with C6 and up suggests a problem related to boiling point - or being able to partition the compunds off of the stationary phase, which will not necesarily be the boiling point, but a temperature where the partitioning favors the vapor phase. And if you are getting good retention (not peak shape - but k value) of propane on this column at 150 degrees, you are going to need some heat to move toluene. You can run this column up to 320 deg. C.

A column defect will show first in the higher alkanes and molecular weights.

Rod