Bioethanol: Determination of Ethanol Content as a Measure of Purity

Specifications for fuel ethanol that bulk producers and blenders must meet are outlined in ASTM D4806. This standard also requires bulk ethanol producers to render the fuel ethanol unfit for human consumption by adding a denaturant, typically natural gasoline. ASTM D4806 requires the fuel ethanol to contain a minimum of 92.1% ethanol by volume, with the denaturant volume ranging from 1.96% to 4.76%. Producers and blenders must monitor and report the content of ethanol and the denaturant to show they are in compliance. The GC-FID analytical procedure for measuring ethanol content in fuel ethanol can be found in ASTM D5501.

Once peak identifications are established, the quantitation of ethanol in samples may begin. To perform this, a mixture containing known amounts of each alcohol in proportion to what is expected in the final blend is injected into the GC column, using n-heptane as a solvent. Retention times of the fuel ethanol sample are then compared to the analytical standard to verify identity.

ASTM D5501 specifies the use of a long poly(dimethylsiloxane) capillary column, such as our Petrocol DH 150. These non-polar columns have considerable theoretical plate numbers and are designed for detailed hydrocarbon analysis (DHA). They are characterized by high efficiency and great reproducibility.