The Construction of Castor Oil (Ricinus communis L) Polyurethane Membrane Embedded 1,10-phenanthroline Graphene as a Cr³⁺ Ion Selective Membrane

A Cr³⁺ ion selective electrode (ISE) based on a polyurethane (PU) membrane from castor oil modified with the active substances 1,10-phenanthroline and graphene was constructed. The ISE consisted of an internal solution with an optimum composition of 0.1 M KCl:Cr(NO₃)₃ and showed a sensitivity of 20.37 ± 0.51 mV decade⁻¹. Spectroscopic analysis showed that urethane bonds were observed at wave number 3390 cm⁻¹ and 1,10-phenanthroline bonds, proven by the aromatic C=C and C-N bonds, respectively at 1600 cm⁻¹ and 1325 cm⁻¹. The modified PU membranes showed a decrease in crystallinity. However, increased crystallinity was observed when the membrane was in a solution of Cr(III) ions. Furthermore, the membrane exhibited a homogeneous solid outer layer structure and a hollow inner layer. The Cr(III) ISE can measure Cr³⁺ ion concentrations in the range of 10⁻¹¹-10^-5 M with coefficient of determination, detection limit, and response time of 0.996, 10^-11 M, and 180 s, respectively. The ISE showed a stable response in the pH range of 5-7. The selectivity of ISE Cr³⁺ towards foreign ions did not interfere with measurements with K_ij values less than 1. In addition, the Cr³⁺ ISE demonstrated good reproducibility and repeatability with an average standard deviation value of less than 5%.