Simultaneous Determination of Monoatomic Ions via Infrared Attenuated Total Reflection Spectroscopy in Aqueous Solution at Different Temperatures

In this study, monoatomic and thus IR-inactive ions were determined via infrared attenuated total reflection (IR-ATR) spectroscopy including Cl − , Na + , Mg 2+ , Ca 2+ , K + and Br − , next to the IR-active ion [Formula: see text]. The determination of IR-inactive ions is enabled, as each ion influences the infrared spectrum of bulk water by organizing the water molecules within the solvation shell around the ionic species in a unique way. Furthermore, the influence of temperature was taken into account for the potential application of this analytical technique in real-world scenarios. Using chemometric data analysis, seven ions could be discriminated at temperatures ranging between 3 ℃ and 45 ℃. Finally, within a sample of seawater, Cl − , Na + , Mg 2+ and [Formula: see text] could be simultaneously quantified, while the concentrations of Ca 2+ , K + and Br − remained below the achievable limits of detection.