Search

This paper investigates using an optical measurement method to determine the concentration ratio in a liquid mixture of methanol and ethanol. To better understand the relative mixture solution concentration, the dilution method is used to determine slight variations in the refractive index of the variable mixture concentration. The test concentration range of both methanol and ethanol is between 0–90%. The results of our analysis indicate that the refractive index of a mixture of methanol and ethanol lies in the interval between the refractive index of pure ethanol and methanol. The optical property of the mixture is similar to that of the solution material with the highest quantity. Regression analysis using a quadratic function resulted in an error of 25%. Regression analysis using a cubic function reduced the error to 6.25%. Therefore, the regression analysis function used in this study is the cubic function, as the mixture solution includes the methanol liquid. Combining the optical measurement and dilution methods can yield the solution concentration of the liquid mixture.

This study develops a high precision non destructive measurement technique based on a laser interferometer for determining the mixture of methanol and ethanol from its refractive index. The optical metrology system is employed to measure the refractive indexes of mixture sample with known methanol and ethanol. The ratio set of the mixture sample have seven sets. The refractive index of the ethanol solution with the methanol alcohol is reduced. When the mixture solution includes the methanol and ethanol, the refractive index of the mixture solution is between the refractive index of the ethanol and methanol. When the refractive index of the solution is very close the refractive index of the ethanol alcohol, the effect of the mixture solution in refractive index is very small. From this experimental result, the effect of the refractive index of the mixture solution in the refractive index of the ingredient liquid is very clear.

This study develops a high-precision, nondestructive measurement technique based on a laser interferometer for determining the methanol concentration of a liquid solution from its refractive index. The optical metrology system is employed to measure the refractive indexes of samples with known methanol concentrations ranging from 0 ~ 90%. The error between the experimental refractive index and the literature refractive index is small than 0.00062. The error between the measured value of the refractive index and the analytically derived value is reduced form 0.00064 to 0.00007. The decreased error ratio is about 89%. When the relative function between the refractive index and methyl alcohol concentration is cubic, this can reduce the regressional analysis error. By applying regressional analysis to the experimental results, an analytical expression is derived to describe the cubic relationship between the refractive index and the methanol concentration. An excellent agreement is observed between the experimentally determined values of the methanol concentration and the analytically predicted results.