In this paper, we report novel ferrocene-functional thiophene compound (Thi-Fc) and ferrocene side-functional styrene copolymer (P3) as chemical probes for the sensing of phosphate anions via electrochemistry. Besides, selectivity of these ferrocene-appended structures for phosphate ions against Br-, Cl-, and ClO43- were also investigated. These ferrocene-functional molecules were built through 1,3-dipolar cycloaddition reaction between azide-functional groups of their precursors and ethynylferrocene. Their CV experiments showed that both Thi-Fc and P3 have diffusion-controlled redox behavior and Fe2+/Fe3++ redox couple undergoes a quasi-reversible process. They responded to the addition of H2PO4 and HP2O73- anions in the form of their n-Bu4N+ salts by shifting their redox potentials cathodically. The ratio of apparent association constants (K(+)/K-(0)) for Thi center dot H2PO4- (80.06), Thi center dot HP2O73- (12.29), P3 center dot H2PO4- (12,944.94) and P3 center dot HP2O73- (1040.40) indicated that P3 gave stronger responses to the addition of both salts. Additionally, the interactions of HP2O73- anions with Thi-Fc and P3 are found out to be weaker than those of H2PO4- as indicated by K(+)/K-(0) values of the corresponding complexes. The obtained K(+)/K-(0) values for Br-, Cl-, and ClO43- anions are very low with respect to those for phosphate anions, indicating Thi-Fc and P3 are selective for phosphate anions against Br-, Cl-, and ClO4(3)(-). (C) 2013 Elsevier B.V. All rights reserved.