A dual-wavelength Mach-Zehnder interferometer technique is used for the investigation of thermodiffusion through 5 mass% NaCl solution at temperature differences of 3 degrees C, 5 degrees C, and 8 degrees C applied across the cavity. Initially, the values of thermal diffusivity and thermodiffusion coefficients are measured from the highly sensitive data of temperature and concentration distribution through sensitivity analysis. Variation of the extent of concentration gradient with time in response to the applied temperature gradient is determined. Interestingly, the extent of separation of the chemical species through the cross effect of the diffusion flow is found to increase with the strength of the applied thermal field.