Novel hydrogen bonding diamide receptors viz., N,N'-bis(phenyl)iso phthalohydrazide (1) and N,N-1-bis(2,4-dinitrophenyl)isophthalohydrazide (11), have been synthesized and characterized by IR, H-1 NMR and elemental analysis. Spectroscopic investigations indicate high affinity of these receptors for carbonate ion. Polyvinyl chloride (PVC) based membranes of (1) and (11) using tridodecylmethyl ammonium chloride (TDDMACl) as cation discriminator and diethylphthalate (DEP), dioctylphthalate (DOP), 1-chloronapthalene (CN), tris(2-ethylhexyl)phosphate (TEHP) and bis(2-ethylhexyl)sebacate (DOS) as plasticizing solvent mediators were prepared and investigated as CO32- selective sensors. The best performance was shown by the membrane of composition (w/w) of (II) (4%):PVC (33%):CN (60%):TDDMACl (3%). This sensor works well over a wide concentration range 1.3 x 10(-7) to 1.0 x 10(-3) M with Nemstian compliance (29.0 mV decade(-1) of activity) at pH 8.6 with a fast response time of similar to 7s and showed good selectivity for carbonate over a number of anions. The sensor exhibits adequate shelf life (two and half months) with good reproducibility (S.D. +/- 0.3 mV) and could be used successfully for the determination of total inorganic carbon in water samples. (c) 2006 Elsevier Ltd. All rights reserved.