Chromatography Forum

Hello all,

Looking for advice regarding GC columns to use to separate the fluoro- positional isomers (i.e. 2-, 3-, and 4-) of amphetamine, methamphetamine, and methcathinone.

The general use column in our lab is a 30 m x 0.25 mm I.D. x 0.25 um thickness HP-5ms column. Running a very slow temperature ramp and a slightly decreased flow (He carrier) I was able to get resolution of about 1.5 but I was hoping I could do better.

My first thought is to keep everything the same except column length (go to 60 m). Anybody have any (bolder) suggestions?

If you leave the amine functional group active (underivitized) the positional isomer differences will be so slight in comparison to the amino group it will be very difficult to separate them. Trifluoropropyl methyl silicone phases or wax phases are good choices to try. You can probably find chromatograms on Restek's web site for these analyte isomers. If not try Supelco or Alltech.

The other choice is to use a chiral phase. Call Supelco for suggestions or chromatograms. A call to tech service is free 800 number.

best wishes,

Rod

If you are not willing to use other column, try derivatizing with MSTFA and test it out?