A new method has been developed that allows measurement of the concentration of solutes with polar groups in the bulk of suitable organic solvent phases as well as at the interface of this phase with an aqueous phase. The measuring method is based on the production of alpha particles and gamma rays by means of (n,α) and (n,γ) reactions in the liquid phase, in which boron or lithium compounds are solved. The alpha particles and gamma rays are detected by means of liquid scintillation. The separation of the pulses is carried out by means of pulse-shape analysis. This method can also be applied to the estimation of the interfacial area of liquid-liquid systems, since the intensity of the light emission of the scintillation solution is proportional to the interfacial area.