Auro Atsushi Tanaka

Amperometric sensor for nitrite using a glassy carbon electrode modified with alternating layers of iron(III) tetra-(N-methyl-4-pyridyl)-porphyrin and cobalt(II) tetrasulfonated phthalocyanine.

The development of a highly sensitive amperometric sensor for nitrite using a glassy carbon electrode modified with alternated layers of iron(III) tetra-(N-methyl-4-pyridyl)-porphyrin (FeT4MPyP) and cobalt(II) tetrasulfonated phthalocyanine (CoTSPc) is described. The modified electrode showed an excellent catalytic activity and stability for the nitrite oxidation decreasing the peak potentials about 200mV toward less positive values and presenting much higher peak currents than those obtained on the bare GC electrode. A linear response range of 0.2-8.6mumoll(-1), with a sensitivity of 0.37muAlmumol(-1) and detection limit of 0.04mumoll(-1) were obtained with this sensor. The repeatability of the proposed sensor, evaluated in term of relative standard deviation, was verified to be 1.4% for 10 measurements of 0.2mumoll(-1) nitrite solution. Interference caused by common ions has been investigated in simulated mixtures containing high concentration level of interfering ions and the sensor was found to be tolerant against these ions. The developed sensor was applied for the nitrite determination in water samples and the results were in agreement with those obtained by a comparative method described in the literature. The average recovery for these samples was 100.1 (+/-0.7)%.

Tris (2,2?-bipyridil) copper (II) chloride complex: a biomimetic tyrosinase catalyst in the amperometric sensor construction

The use of tris (2,2?-bipyridil) copper (II) chloride complex, [Cu(bipy)3]Cl2/6H2O, as a biomimetic catalyst, is reported in the construction of an amperometric sensor for dopamine. The sensor was prepared modifying a glassy carbon electrode with a Nafion † membrane doped with the complex. The optimized conditions for the sensor response were obtained in 0.25 mol dm � 3 Pipes buffer (pH 7.0) containing 150 mmol dm � 3 H2O2, with an applied potential of � /50 mV versus saturated calomel electrode (SCE). In these conditions, a linear response range between 9 and 230 mmol dm � 3 , with a sensitivity of 1.439 /0.01 nA dm 3 mmol � 1 cm � 2 and a detection limit of 4.8 mmol dm � 3 were observed for dopamine. The response time for this sensor was about 1 s, presenting the same response for at least 150 successive measurements, with a good repeatability (4.8%) expressed as relative standard deviation for n � /13. After its construction, this sensor can be used after 180 days without loss of sensitivity, kept at room temperature. The difference of the sensor response between four preparations was 4.2%. A detailed investigation about the sensor response for other eighteen phenolic compounds and five interfering species was performed. The sensor was applied for dopamine determination in pharmaceutical preparation with success. # 2002 Elsevier Science Ltd. All rights reserved.

Anodic oxidation of cysteine catalysed by nickel tetrasulphonated phthalocyanine immobilized on silica gel modified with titanium (IV) oxide

Abstract A chemically modified electrode constructed by mixing nickel tetrasulfonated phthalocyanine (NiTsPc) immobilized on modified silica gel with carbon paste showed a redox process with a midpoint potential of 0.44 V vs sce . Experiments carried out with different supporting electrolytes suggested an effect due to the nature of the anion. The solution pH does not affect the midpoint potential but the peak current increases when the pH is decreased. The immobilization procedure causes an increase in the monomeric form of the complex. The electrochemical property of NiTsPc adsorbed onto modified silica showed good stability even in acidic media (pH=2) and the ability to catalyze the electro-oxidation of cysteine at 0.5 V vs sce .

Electrochemical Sensor for Hydrazine Based on Silica Modified with Nickel Tetrasulfonated Phthalocyanine

Nickel tetrasulfonated phthalocyanine (NiTsPc) immobilized onto titanized silica gel (ST) showed good stability and redox properties. The cyclic voltammograms obtained with a carbon paste electrode modified with ST-NiTsPc presented an enhanced peak current at 450 mV (vs. SCE) which did not shift with solution pH. The redox process was attributed to NiII/NiIII, which presented a good electrocatalytical activity for oxidizing hydrazine in neutral solution. The process is controlled by the electron transfer step and no diffusion limitation was observed. The modified electrode was very sensitive for hydrazine, giving a detection limit of 1.0 × 10−5 mol L−1, for an applied potential of 450 mV (vs. SCE). A linear response range was observed between 1.0 × 10−4 and 6.0 × 10−4 mol L−1, fit by the equation I = −0.1 (± 0.1) + 7.9 (± 0.3) [Hydrazine], with a correlation coefficient of 0.998 for n = 6. The repeatability for 11 measurements was excellent, with a relative standard deviation of 3.7 %. The active material, nickel tetrasulfonated phthalocyanine modified silica, was stable for at least 6 months, losing only 10 % of its signal over this period.

Development of an amperometric sensor for phenol compounds using a Nafion † membrane doped with copper dipyridyl complex as a biomimetic catalyst

Abstract The use of [CuDipyCl 2 ] as a biomimetic catalyst in the construction of an amperometric enzymeless biosensor for phenol determinations is reported. The sensor was prepared modifying a glassy carbon electrode with a Nafion® membrane doped with [CuDipyCl 2 ]. The sensor presented a higher response for dopamine in 0.1 mol l −1 phosphate buffer at pH 7, with an applied potential of −50 mV versus SCE. With the optimized operational conditions a linear response range between 4.0×10 −5 and 6.0×10 −4 mol l −1 , with a sensitivity of 350±10 nA l mmol −1 cm −2 and a detection limit of 9.0×10 −6 mol l −1 were observed for the sensor. The response time presented for this sensor was approximately 1 s, presenting the same response for at least 50 measurements, with good repeatability (R.S.D. 3.8%, for n =9). The difference of the response between four preparations was 7%. Detailed investigations of the sensor response for monophenol and diphenol compounds and interfering species were carried out.

Underpotential deposition of copper and its influence in the oxygen reduction on platinum

Abstract The underpotential deposition (UPD) of Cu on Pt was studied in acid media using cyclic voltammetry and rotating ring-disk electrode techniques. Experimental data at sub-monolayer levels demonstrate that ad-atom formation occurs in different energy states and no rearrangements take place in the ad-layer. Rotating ring-disk studies of the oxygen reduction reaction on Cu UPD show a strong inhibition of the reaction only in the region of diffusion control. At first, the 4 e reaction to H 2 O is inhibited in favor of the 2 e reaction to H 2 O 2 but at more negative potentials even the formation of H 2 O 2 is inhibited. A mechanism based on the degree of surface-active sites blocked by Cu ad-atoms is proposed.

Amperometric sensor for nitrite based on copper tetrasulphonated phthalocyanine immobilized with poly-L-lysine film.

In this work, an amperometric sensor for nitrite detection based on a glassy carbon electrode modified with copper tetrasulphonated phthalocyanine immobilized by polycationic poly-L-lysine film is presented. The modified electrode showed an excellent catalytic activity toward nitrite oxidation. A linear response range from 0.12 up to 12.20 micromol L(-1) was obtained with a sensitivity of 0.83 microA L micromol(-1). The detection limit for nitrite was 36 nmol L(-1). The repeatability of the proposed sensor, evaluated in terms of relative standard deviation, was 1% for 10 measurements of 10 micromol L(-1) nitrite solution. Finally, the developed sensor was applied for nitrite determination in water samples and the results were in agreement to the comparative method. The average recovery for the samples was 101 (+/-4)%.

Iron(III) tetra-(N-methyl-4-pyridyl)-porphyrin as a biomimetic catalyst of horseradish peroxidase on the electrode surface: An amperometric sensor for phenolic compound determinations

The use of iron(III) tetra-(N-methyl-4-pyridyl) porphyrin (FeIIIT4MpyP) and histidine (His) in the construction of an amperometric sensor for phenolic compound determinations is reported, based on horseradish peroxidase (HRP) chemistry. The sensor was prepared by modifying a glassy carbon electrode with Nafion membrane doped with FeIIIT4MpyP and His, in a mass ratio of 1:2. The sensor presented its best performance at 50 mV vs. SCE in 0.1 mol l(-1) succinate buffer (pH = 4.0) containing 125 micromol l(-1) H2O2. Under optimized operational conditions, a linear response range from 0.6 to 6.0 micromol l(-1) was obtained with a sensitivity of 61 nA cm(-2) micromol l(-1). The detection limit for catechol determination was 0.35 micromol l(-1). The response time was less than 0.5 s. The proposed sensor presented stable responses for 100 successive determinations, while satisfactory responses were observed even after 200 measurements. The repeatability, evaluated in terms of relative standard deviation, was 4% for n = 7. The signal responses for other phenolic compounds, including those of environmental and clinical interest, were also investigated.

Electrocatalytic Oxidation and Voltammetric Determination of Hydrazine in Industrial Boiler Feed Water Using a Cobalt Phthalocyanine-modified Electrode

Abstract A carbon paste electrode modified with cobalt phthalocyanine (CPECoPc) was developed and applied to the determination of hydrazine [N2H4] in industrial boiler feed water. The CPECoPc exhibited good electrocatalytical activity for hydrazine oxidation at pH 13. A linear correlation was obtained between anodic peak current (Iap) and hydrazine concentration in the range of 1.25 × 10−4 to 9.80 × 10−4 mol L−1, fit by the equation Iap = 1.47 + 4.90 × 105 [N2H4] with a correlation coefficient of 0.9967. A detection limit of 7.35 × 10−5 mol L−1 was obtained. Recovery of hydrazine from three samples ranged between 99.0% and 102.9%. The modified electrode showed no interference by cations commonly present in boiler water, such as K+, Na+, Ca2+, Mg2+, Al3+, Pb2+, and Zn2+. The results obtained for hydrazine in boiler water using the proposed modified electrode are in agreement with the data obtained by a standard spectrophotometric method, at the 95% confidence level.

Dissolved oxygen amperometric sensor based on layer-by-layer assembly using host–guest supramolecular interactions

The development of a simple, efficient and sensitive sensor for dissolved oxygen is proposed using the host-guest binding of a supramolecular complex at a host surface by combining a self-assembled monolayer (SAM) of mono-(6-deoxy-6-mercapto)-beta-cyclodextrin (betaCDSH), iron (III) tetra-(N-methyl-4-pyridyl)-porphyrin (FeTMPyP) and cyclodextrin-functionalized gold nanoparticles (CDAuNP). The supramolecular modified electrode showed excellent catalytic activity for oxygen reduction. The reduction potential of oxygen was shifted about 200 mV toward less negative values with this modified electrode, presenting a peak current much higher than those observed on a bare gold electrode. Cyclic voltammetry and rotating disk electrode (RDE) experiments indicated that the oxygen reduction reaction involves probably 4-electrons with a rate constant (k(obs)) of 7 x 10(4) mol(-1) Ls(-1). A linear response range from 0.2 up to 6.5 mg L(-1), with a sensitivity of 5.5 microA L mg(-1) (or 77.5 microA cm(-2) L mg(-1)) and a detection limit of 0.02 mg L(-1) was obtained with this sensor. The repeatability of the proposed sensor, evaluated in terms of relative standard deviation was 3.0% for 10 measurements of a solution of 6.5 mg L(-1) oxygen.