Synthesis and characterization of Schiff base have been carried out from the reaction of salicylaldehyde and 2,4-dinitrophenylhydrazine (DNPH) using HCl 37% catalyst. 0.495 g (2.5 mmol) DNPH was added to 0.3 mL (2.5 mmol) salicylaldehyde in 50 mL methanol solvent and 1 mL of HCl 37% catalyst was added. The result of the synthesis of Schiff Base is used as a carbonate ion sensor (CO32-) in the sā¦