Hello, you can seperate ethanol and methanol in GC using a DB5 capillary column with a thick stanionary phase (> 0.5 µm) and low starting temperature (30 °C) or DB WAX ( 30 m × 0.53 mm ×1 mm)

Other chromatographic conditions also influence your separation - in general mobile phase flow (and type of mobile phase) and isothermal vs. programmed temperature are the main factors influncing separation of analytes (together with type of stationary in your column).

Based on the chemical structure of menthol and ethanol, these analytes should be separated by GC easily.

When you have your first chromatogram where menthol and ethanol are not separated, you need to change isothermal part and/or temperature rate before the elution time of these compounds.

Please do the Google search and you will find any answer you want.

https://www.phenomenex.com/Application/Detail/15427

https://www.phenomenex.com/Application/Detail/16667

If I understand you correctly you are diluting methanol and decanol in ethanol and you want to separate methanol and decanol from ethanol. Might I suggestion you pick a different solvent?

Thanks all.....

I will work on the advice and method given and later revert.