The main aim of this work is to improve the lower detection limit of cadmium selective polymeric membrane. The sensor was fabricated by using thiacalixarene derivative 5,11,17,23-tetratert-butyl-25,27-bis-[(3′-methoxy phenyl)methoxy]-26, 28-dihydroxy-2,8,14,20-tetrathiacalix [4]arene as ionophore. The membrane with composition of ionophore: PVC: DMP: NaTPB of 3.5% : 33% : 1.0% : 62.5% (w/v) has a standard detection limit of 1.0x10 -8 M and lowest possible detection limit of 6.2x10 -9 M. The

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... trode exhibits Nernstian response with slope 35.3±1 mV decade -1 of activity in linear concentration range of 4.2x10 -8 to 1.0x10 -1 M for Cd 2+ ion, performs satisfactorily over wide pH range (1.5-7.0), with a fast response time (5s). The selectivity coefficients determined by using fixed interference method (FIM) indicate high selectivity for Cd 2+ as compared to other tested cations. The practicable utility of electrode has been demonstrated in the titration of Cd 2+ with standard EDTA solution. The proposed electrode was successfully used for the determination of Cd 2+ in different biological and environmental samples.