Ethanol is conveniently determined in aqueous solutions by gas chromatography (GC). Gas chromatography is a method of separating volatile compounds so that they may be detected individually in complex mixtures. Compounds are separated based on differences in their vapor pressures and their attraction to solid materials inside the instrument. A typical GC system is illustrated in Figure 1. In GC, the sample is injected into the instrument using a small syringe. The sample is swept into the instrument using a carrier gas. Separation is achieved by both attraction to the stationary phase and differences in vapor pressure. A detector is at the exit of the column. Because the analyte molecules bind differently to the stationary phase, they travel through the GC column at different rates. That is, they have different retention times on the column. As an analyte appears in the detector, its presence
is signaled by a peak. Thus, a gas chromatogram consists of a series of peaks, one for each of the components of the sample. The chromatogram is displayed on a computer screen.
conveniently determined