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


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