Structural and optical properties of various liquid samples are of particular importance for both chemical and biological applications. These characteristics can be readily obtained from highly accurate, non-destructive ellipsometric measurements in a wide wavelength range. However, for a reliable result, certain technical obstacles must be eliminated for this type of measurement, e.g., excluding the environmental vibrations and providing an aligned liquid surface are both essential. Previously, it was shown that by using an ellipsometric configuration with active pneumatic isolators, it is possible to obtain vital structural information from both liquid-air and liquid-liquid interfaces, revealing nanoscale surface structures. In this work, the method is further extended by incorporating infrared ellipsometry, expanding the accessible spectral range into the mid-infrared region for enhanced surface and compositional analysis.