Additionally, a supersaturated solution of MgSO 4 was prepared from MgSO 4 heptahydrate 98 % (Sigma-Aldrich, Gillingham, UK) dissolved in Milli-Q water (IQ 7000, Merck, Darmstadt, Germany, resistivity 18.2 MΩ • cm), and filled into a well-sealed petri dish. The petri dish was left in a fume hood at 20 • C until crystals formed. This process was to mimic the crystallisation process in the crystallisation cell. Due to constraints of the set-up it was impossible to investigate crystals grown directly in the microfluidic cell at cryogenic temperatures. The crystals grown in the petri dish were made into pellets using the method described above and characterised at cryogenic temperatures with terahertz spectroscopy later to confirm their structure more accurately.