The newly established set up, based on microfludics and THz-TDS, has been applied to develop the proposed method of measuring solute concentration as well as the local concentration of semi-crystalline systems. By acquiring terahertz spectra of liquid samples with different concentrations at various temperatures, the calibration curve was determined by the extracted absorption at terahertz frequencies. This was then used to calculate the concentration of solutions. Furthermore, this method can also be applied to study local concentration of the liquid phase while crystallisation occurs. Using the absorption at lower frequencies is recommended in this case, since the complexity of entangled spectral features of liquid and crystalline phases at higher frequencies complicates the spectra. THz-TDS can hence be used as a complementary method for studying concentration changes in a variety of systems under different conditions.