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Penicillamine is a chelator class of pharmaceutical. It is a metabolite of penicillin, although it has no antibiotic properties. To treat rheumatoid arthritis, penicillamine is used as a form of immunosuppression. It works by inhibiting macrophage function, reducing numbers of T lymphocytes, preventing collagen from cross-linking, and decreasing rheumatoid factor. It is used as a chelating agent. For example in cystinuria, a hereditary disorder featuring formation of cystine stones, penicillamine binds with cysteine to yield a mixed disulfide which is more soluble than cystine. Penicillamine has been used to treat mercury poisoning [1]. Carbon nanotubes (CNTs) continue to receive considerable attention in electrochemistry. Recently, carbon nanotubes have been introduced as electrocatalysts and CNTs modified electrodes have been reported to give super-performance in the study of a number of biological species [2, 3].The determination of penicillamine in biological fluides is important. A major obstacle usually encountered in the electrochemical determination of penicillamine in biological fluieds is the interference of uric acid, which are usually present at high concentrations and can be oxidized at a potential close to that of penicillamine. In this work, we proposed aminophenol as a mediator and multiwall carbon nanotubes-Ti02 as a sensor for a rapid, sensitive and highly selective amperometric determination of penicillamine in the presence of uric acid. Fig. 1 displays a typical morphology of a) p-aminophenol-multiwall carbon nanotubes-Ti02 (/J-APMCNTPE-Ti02), b) carbon nanotubes paste electrode (CNPE), and c) carbon paste electrode (CPE) characterized by SEM. As shown in Fig. l,p-aminophenol and Ti02 on the surface of CNTs did not change CNTs' morphology, but only made it more compact. The electrochemical behaviors of penicillamine at the surface of this modified electrode was studied using cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy. Cyclic voltammograms of different electrodes in 0.1 mol L-1 PBS (pH 6.0) with and without PA in the solution are shown in Fig. 2. The results indicated that the chemically modified electrode exhibited an efficient electrocatalytic activity towards the oxidation of penicillamine. The peaks potential of penicillamine and uric acid can be separated from each other with a potential difference of 215 mV between them using differential pulse voltammetry. These conditions are sufficient to allow determination of penicillamine in the presence of uric acid. At pH 6.0, the catalytic peak current was linearly dependent on penicillamine concentration in the range of 0.04-200 �mol L-1 penicillamine. Detection limit for penicillamine was 0.01 �mol L-1 . The RSD% for 0.12 and 1.5 �mol L-1 penicillamine were 1.6% and 2.1%, respectively. Finally, the sensor was also examined as a selective, simple and precise new electrochemical sensor for the determination of penicillamine in real samples in the presence of uric acid such as drug and urine.

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