The reaction progress was followed in situ at 20 °C by measuring pH as protons were released during precipitation (Eq. 1). The pH was continuously measured with a pH electrode connected to a data logger board DrDAQ with a time resolution of 1 s (Pico Technology, Cambridgeshire, UK). The measured pH ranged from the initial 0.1 M DAP solution at around 8.0 to the end of precipitation at 5.8. Before the experiments, the pH electrode was calibrated against buffer solutions.