An automated FIA system to determine alcoholic grade in beverages based on Schlieren effect measurements using an LED-photocolorimeter

Abstract

Alcoholic grade determination in beverages is usually carried out by laborious, slow and expensive processes such as distillation or chromatographic measurements. To overcome these drawbacks, a simple, automated, flow injection system using a photocolorimeter based on a light-emitting diode (LED) as source of radiation and a phototransistor as photodetector is proposed. The alcohol determination is based on refractive index gradient (Schlieren effect) measurements when beverages are injected into an inert carrier stream (water) of a FIA configuration that presents limited mixing conditions. The system was applied to wine, gin, rum, vodka and sugar cane-based beverages known as “cachaça” available in Brazil. The alcoholic grade determination in these alcoholic beverages showed a relative standard deviation of 3.4% and a mean relative error of 3.0% (n = 10). The developed system processes 120 samples per hour with consumption of 250 μl of sample and no reagent or distillation process is necessary in carrying out the analysis.