Application of optical methods to determine the concentration of sugar solutions

Abstract

Two optical methods were used to determine the concentration of sugar (sucrose) solution. The first employed a hollow perspex prism, a prism spectrometer and a monochromatic light source. The angles of minimum deviation for different sugar samples were determined, whose values were used to compute the refractive indices of these samples. The relationship between the refractive indices and the sugar concentrations of the samples was found to be linear. The effect of temperature on the refractive index of the solutions was also investigated and it was found that the relationship is linear with a negative gradient. The temperature coefficient of refractive index was determined and was found to be in agreement with the expected result.

The second method employed the use of a half-shade polarimeter to determine the optical rotation of different sugar samples. The relationship between the angle of optical rotation and the concentration of the solutions was found to be linear. The optical rotatory power of sugar solution was also determined and found to be in agreement with the expected result and with results from other researchers. The two methods were also used to determine the sugar concentrations in raw sugar, orange and apple juices. It was found that the concentration of sugar in these fluids was almost the same.

The two methods were therefore found to be reliable.