A new technique, based on Optical Methods, has been tested for the evaluation of the lithium bromide (LiBr) concentration, a corrosive substance frequently used in heat pumps. Those solutions have large oxidizing capabilities. This technique avoids the direct contact between the electrodes and the LiBr aqueous solution within a thermodynamic absorption cycle. The viability of this technique in a potential commercial device, resides on its capability to detect working fluid concentrations within a temperature range from 25 °C up to 70 °C, those limiting temperature values correspond to the operating wavelengths of 1.33 μm and 1.55 μm, respectively. Our system determines the correlation among the signal and temperature data, for various concentrations, between 49 and 58 mass percentages. This function of two variables is represented as a surface with the transmittance, concentration and temperature as parameters and wavelength as reference. We discuss the adequate parameters characterization used in this technique.