Spectrophotometric determination of ethanol in liquors using erythrosine lactone

Spectrophotometric determination of ethanol in liquors using erythrosine lactone was examined. Erythrosine was extracted from acidic solution into hydrophobic organic solvents as a colorless species of lactone type. An orange color was developed by the addition of a small quantity of alcohol into the extract. When this solution was mixed with water, the color was distributed into both phases, the water and the organic solvent. Photometric measurement was carried out using the water phase to determine the content of ethanol. This method had two weak points. One was lack of reproducibility owing to the temperature dependence of the distribution. The other was that this method was not able to be applied to colored liquors. Another method was investigated. When an aqueous solution of approximately 2M HCl was added to the liquor phase, colored species of erythrosine remained in the organic phase. Photometric determination was performed by using the organic solvent phase. By this method the ethanol content of colored liquors was determined without distilling. The analytical results on some liquors agree well with the labeled values on bottles.