DW-WAX column - analyse methanol in water:isopropanol (95:5). UNEXPECTED peak!!!

Hello, Im using DW-WAX column (30m, 0,53mm, 1um). I was trying to analyse methanol in water:isopropanol (95:5). I have huge problem, in my desorbent always is methanol peak and it is big.. the weidrest is that this peak in 1st inj has area about 10, next inj - peak is bigger, sometimes area 200.. then 3rd inj peak has area about 25 and over and over again.
What could be the problem? Any idea how can I remove it? The program is isotermal - 50*C for 5 min, detector temp=250*C and injector temp=200*C.

Please heeeelp!

Parents Reply Children
  • I inject 1uL.

    what about solvent expansion? it is inj 1ul, isnt it too big? 

  • 1ul of any sample that has water in it is too large for a typical split/splitless system due to the huge expansion of water when it vaporizes.Take a look at one of those vapour volume calculators to prove it to yourself. I think the GC software may have one built in.

    Have you tried headspace for this analysis. Even manual headspace might work if you have a suitable internal standard. Fill an autosampler vial up to just under 1 ml with the sample (containing the IS), leave it at room temperature for a while and then using a gas tight syringe inject some of the headspace into the GC. It works surprisingly well. We were able to measure ethanol in Kombucha this way very successful

    Kevin

Was this helpful?