Efficient electrocatalytic detection of epinephrine at gold electrodes modified with self-assembled metallo-octacarboxyphthalocyanine complexes

Electrocatalysis of epinephrine at gold electrode pre-modified with the self-assembled monolayer of cysteamine and subsequently integrated with novel metallo-octacarboxyphthalocyanine (MOCPc where M=Fe, Co and Mn) complexes (Au-Cys-MOCPc) was investigated. The electrodes showed response to the presence of epinephrine. The oxidation peak potential (E-p/V vs. Ag vertical bar AgCl, sat'd KCl) and charge transfer resistance (R-ct (k Omega)) in epinephrine solution depend markedly on the central metal of the phthalocyanine cores: Au-Cys-FeOCPc < Au-Cys-MnOCPc < Au-Cys-CoOCPc. All the electrodes showed first order electrode kinetics in [epinephrine]; the Au-Cys-FeOCPc electrode exhibited catalytic rate constant (k(ch) - 4.1 x 10(7) M-1 s(-1)) which is higher than that of the Au-cys-CoOCPc or Au-cys-MnOCPc electrode. Mechanism, recognizing the mediation of the electrocatalytic process by the central M(II)/M(III) redox processes was proposed. Epinephrine electro-oxidation at the Au-cys-FeOCPc electrode was studied in more details for the response characteristics. The diffusion coefficient of epinephrine was evaluated as (2.62 +/- 0.23) x 10(-1)cm(2) s(-1). it was established that Au-Cys-FeOCPc is suitable for sensitive determination of epinephrine in physiological pH (7.40) conditions showing linear concentration range of up to 300 nM, with excellent sensitivity (0.53 +/- 0.01 nA nM(-1)), and very low limits of detection (13.8 nM) and quantification (45.8 nM). The peak separation between ascorbic acid and epinephrine is large enough (190 mV) to permit simultaneous determination of both epinephrine and ascorbic acid in physiological pH 7.4 conditions using the Au-cys-FeOCPc electrode. Au-cys-FeOCPc electrode was successfully used for the determination of epinephrine in epinephrine hydrochloric acid injection with recovery of ca. 98.4%.