Once solution was injected into the liquid cell and the temperature had stabilised at the setpoint temperature (here ∼ 4 °C), the temperature of the cell was slowly increased at a rate of 1 °C min -1 up to 25 °C. In the present study, calibration was therefore performed in the temperature range of 4 °C to 25 °C and the concentration region that was explored ranged from 0 (pure water) and 0.28 w/w % (MgSO 4 to water). The weight ratio/concentration is denoted as c (w/w %), which represents the concentration of solution.