Ethanol and methanol levels in biofuels must be accurately determined as they impact fuel performance and influence sales price.
Since fuel ethanol must be denatured with gasoline to render it nonpotable prior to transport, analysis is complicated by the presence of
gasoline hydrocarbons. Testing is usually done according to ASTM Method D5501, which recommends either a 100m or a 150m column.
This method currently targets the determination of ethanol at 93-97% and methanol at 0.1-0.6%, based on mass percent in product; however,
discussions have been initiated to expand the range to 20-99%. The main challenge in ASTM D5501 is getting clean elution of both ethanol
and methanol, without the coelution of components from the gasoline denaturant. Coelution of methanol and isobutane is particularly
problematic and may require time-consuming cryogenic conditions.