Determination of ethanol in liquor by near-infrared spectrophotometry with flow injection

A simple procedure for the determination of ethanol in a liquor by near-infrared (NIR) spectrophotometry with flow injection (FI) is proposed. A liquor sample is equilibrated off-line with dried chloroform to extract ethanol into the organic phase. The extract is injected into a carrier stream of dried chloroform passing through a home-made flow through cell (1 mm path length) sitting in a NIR spectrophotometer for continuous monitoring of absorbance at 2305 or 2636 nm. The ethanol content can be evaluated from a calibration established by a plot of change in absorbance versus concentration of ethanol standard solutions. Optimization of the system will be discussed. A calibration is linear in the range of 20–50% (v/v) ethanol. A throughput of 240 injections h⁻¹ can be obtained. The procedure is validated by comparing the results with an analysis using gas chromatography.