Dependence of Refractive Index on Concentration and Temperature in Electrolyte Solution, Polar Solution, Nonpolar Solution, and Protein Solution

The dependence of refractive index on the concentration and temperature in six kinds of aqueous solutions was investigated. The six solutions were three electrolyte solutions (NaCl, KCl, and CaCl2), a polar solution (glucose solution), a nonpolar solution (ethyl acetate solution), and a protein solution (bovine serum albumin solution). It was found that dn/dc decreased with temperature and dn/dT decreased with concentration in polar, nonpolar, and electrolyte solutions. While in protein solution, both of the derivatives showed an opposite behavior due to the thermal aggregation effect of proteins. According to the experimental results, the empirical expressions of the refractive indices in terms of both concentration and temperature were derived for the six solutions. By having the derivatives of refractive index n with respect to concentration c (dn/dc) and with respect to temperature T (dn/dT) respectively from the expressions, the dependence of (dn/dc) on temperature and that of (dn/dT) on concentration were obtained.