The Construction of Castor Oil (<i>Ricinus communis</i> L) Polyurethane Membrane Embedded 1,10-<i>phenanthroline</i> Graphene as a Cr<SUP>3+</SUP> 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 Kij values less than 1. In addition, the Cr3+ ISE demonstrated good reproducibility and repeatability with an average standard deviation value of less than 5%.