Development of this GC method was started with selection of a
sample solvent that dissolves oleic acid and related fatty acids.
Fatty acids are carboxylic acids with long aliphatic chains. As the
aliphatic chain length increases, the solubility of the fatty acids in
water decreases very rapidly. Methanol, ethanol and isopropanol
are all good solvents for oleic acids (at least 411.6 g/mL), but
methanol and ethanol are more polar alcohols than isopropanol
[21]. GC injection using methanol and ethanol as sample solvents
showed broad peak shapes for some long chain fatty acids due to
the polarity mismatch between the sample solvents and the stationary
phase. The peak shapes of all fatty acids under study were
significantly improved by using isopropanol as sample solvent.
Therefore, isopropanol was selected as sample solvent (diluent).