Improved guanidinium ion-selectivity by novel calix[4]arene and calix[6]arene receptor molecules on CHEMFETs

Poly(vinyl chloride) membrane CHEMFETs incorporating a novel calix[4]arene derivative (1), novel calix[6]arene derivatives (3, 4, 5, 6 and 7), phosphate derivatives of p-tert-butylcalix[4]arene (2) or p-tert-butylcalix[6]arene (8) with variable amounts of hydrophobic anions [potassium tetrakis(4-chlorophenyl)borate (KTCTPB)] have been tested for their response to guanidinium ions in the presence of the interfering ions Na+, K+, NH4+ and Ca2+.The best guanidinium selectivity has been obtained for the CHEMFET based on the 1,3,5-triamide derivative of p-tert-butylcalix[6]arene (4), with dibutyl phthalate as solvent mediator, and 50 mol% KTCTPB with respect to the ionophore. The selectivity coefficients (log KpotGu,j) are the highest reported for guanidinium ions in a potentiometric sensor. The CHEMFETs show an almost ideal Nernstian response in the linear range (slope 58–60 mV decade–1).