Described herein are devices, systems, and methods for determining the composition of liquids, including the identity of one or more drugs in the liquid, the concentration of the drug, and the type of diluent using immittance spectroscopy. These devices, systems and methods are particularly useful for describing the identity and, in some variations, concentration of one or more components of a medical liquid such as intravenous fluid. In particular, described herein are devices, systems and methods that may operate in low ionic strength diluents. Also described are methods of recognizing complex immittance spectrograph patterns to determine the composition of a liquid by pattern recognition.