Air-stream assisted separation and photometric determination of ethanol in wine using an automated flow system

This study presents the design of a multicommuted flow analysis system that utilizes an air stream to separate ethanol from wine samples. The separated ethanol is then oxidized with a dichromate solution, followed by spectrophotometric determination. The design adheres to the principles of green analytical chemistry and focuses on integrating the benefits of multicommuted flow analysis with an emphasis on versatility, robustness, minimal reagent usage, and waste reduction. The experimental setup, controlled by an Arduino Due board with electronic interfaces, was operated using custom software designed for this study. Ethanol molecules were extracted from the sample using an air stream, trapped in a reaction chamber, and subjected to derivatization with potassium dichromate (K₂Cr₂O₇), followed by photometric detection with an LED-based photometer. After optimizing the control parameters, the method's efficacy was confirmed by analyzing ethanol levels in red wine samples. The system demonstrated several advantages, including a linear response range of 2.5-25.0% (r² = 0.999), a detection limit of 0.59% (v/v) ethanol, a coefficient of variation of 1.78% (n = 10) for a 10.0% (v/v) ethanol standard solution, a sampling rate of 36 determinations per hour, a waste generation of 1.0 mL per determination, and a reagent consumption of 17 mg of K₂Cr₂O₇ per determination. Based on the AGREE - Analytical GREEnness Metric Approach, the analytical greenness of the proposed method is estimated to be 66%.