Method and device for determining the alcohol content of aqueous solutions using gas sensors
In order to overcome the limitations of the prior art, according to a first aspect of the invention, a method has been developed capable of providing a rapid and precise evaluation of the ethanol content of hydroalcoholic solutions, including commercial beverages, by measuring the alcohol concentration in a corresponding vapor phase.
According to another aspect of the invention, the proposed method has been reproduced in practice thanks to a specially designed device, suitable to be used for the determination of the alcohol content of solutions and beverages of any strength.
In the method of the invention, the solution to be analyzed is first diluted with water in the liquid phase, so as to minimize the partial pressure of the volatile organic compounds in the corresponding vapor phase. The resulting vapor phase can then be sucked in by means of a device, such as a vacuum pump, and sent to a device capable of mixing this stream with air, such as a venturi injector. The alcohol-enriched air mixture can thus be sent to gas sensors for ethanol analysis, such as semiconductor sensors, to then be discharged into the environment.
The dilution of the vapor phase with air has the advantages of bringing the alcohol content back into the measurement range of commercially available gas sensors and limiting the influence of the humidity of the current to be analyzed on the sensor response. By alternating loading phases, in which the air current is mixed with alcohol vapors, and cleaning phases, in which the air current is sent pure, and possibly heated, to the sensors, it is possible to alternate measurement stages with regeneration stages. sensors, if needed.
Through the use of a calculation module equipped with analog and / or digital pins for output and input communications, such as a single board microcontroller and appropriate circuitry, it is possible to modulate the inlet air flow and the mixing ratio, and analyze the response of the sensors so as to be able to quantify the concentration of alcohol present in the gaseous phase. The sensor response can be correlated to the alcohol concentration in the gas phase through calibration curves constructed from the analysis of solutions whose liquid phase has a known alcoholic concentration and whose concentration of ethanol in the vapor phase has been obtained by means of thermodynamic models and / or by means of known semi-empirical models.
Therefore, for the analysis of a sample of unknown title, the sensor response is linked to the concentration in the gas phase, and then, by means of thermodynamic and / or semi-empirical models already mentioned, it is possible to calculate the unknown ethanol concentration in the liquid phase. In this way, the effect of volatile organic compounds is canceled, the effect of temperature is taken into account (through pure thermodynamic calculation or through the use of semi-empirical equations) and avoids having to dehumidify the current sent to the sensors.
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