Cyclic voltammetric studies of octabutylthiophthalo-cyaninato-cobalt (II) and its self-assembled monolayer (SAM) on gold electrode
- Ozoemena, Kenneth, Westbroek, Philippe, Nyokong, Tebello
- Authors: Ozoemena, Kenneth , Westbroek, Philippe , Nyokong, Tebello
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289567 , vital:56650 , xlink:href="https://doi.org/10.1142/S1088424602000130"
- Description: The synthesis of thiol-derivatized cobalt phthalocyanine complex, 2,3,9,10,16,17,23,24-octa (butylthiophthalocyaninatocobalt(II) (CoOBTPc) is described. Cyclic voltammetric data of this complex in DMF showed five quasi-reversible and reversible, diffusion-controlled redox couples, comprising both the phthalocyanine ring and central metal redox processes. The CoOBTPc complex forms a self-assembled monolayer (SAM) on gold electrode. The investigation of the integrity of this SAM, using the established cyclic voltammetric methods in aqueous alkaline solutions, gave evidence about the formation of a stable and easily reproducible monolayer. However, due to its susceptibility to destruction via oxidative and reductive desorptions, its potential application as an electrochemical sensor in alkaline pH is limited to a potential window of between −0.20 and +0.55 V vs Ag/AgCl.
- Full Text:
- Date Issued: 2002
- Authors: Ozoemena, Kenneth , Westbroek, Philippe , Nyokong, Tebello
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289567 , vital:56650 , xlink:href="https://doi.org/10.1142/S1088424602000130"
- Description: The synthesis of thiol-derivatized cobalt phthalocyanine complex, 2,3,9,10,16,17,23,24-octa (butylthiophthalocyaninatocobalt(II) (CoOBTPc) is described. Cyclic voltammetric data of this complex in DMF showed five quasi-reversible and reversible, diffusion-controlled redox couples, comprising both the phthalocyanine ring and central metal redox processes. The CoOBTPc complex forms a self-assembled monolayer (SAM) on gold electrode. The investigation of the integrity of this SAM, using the established cyclic voltammetric methods in aqueous alkaline solutions, gave evidence about the formation of a stable and easily reproducible monolayer. However, due to its susceptibility to destruction via oxidative and reductive desorptions, its potential application as an electrochemical sensor in alkaline pH is limited to a potential window of between −0.20 and +0.55 V vs Ag/AgCl.
- Full Text:
- Date Issued: 2002
pH study of the electrocatalytic SO2 detection at a glassy carbon electrode modified with iron (II) tetrasulfophthalocyanine
- Thamae, Mamothibe, Westbroek, Philippe, Nyokong, Tebello
- Authors: Thamae, Mamothibe , Westbroek, Philippe , Nyokong, Tebello
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/304786 , vital:58490 , xlink:href="https://doi.org/10.1007/s00604-002-0914-8"
- Description: The electrocatalytic determination of SO2 is studied as a function of pH at a glassy carbon electrode modified with iron(II)tetrasulfophthalocyanine ([Fe(II)TSPc]4−). It was found in the literature that depending on pH, SO2·xH2O, HSO3 − and/or SO3 2− are the main compounds in solution, that these compounds behave differently at the electrode surface, and that the condition of the electrode surface is stable over the entire pH-range. The use of SO2(g) or sodium sulfite as starting material did result in identical curves except in the pH range from 7.5–9.0. A possible explanation could be given by proposing that SO2·xH2O is very unstable in the presence of SO3 2−. In strongly acidic medium, SO2·xH2O is the main compound, which can be oxidized as well as reduced with exchange of two electrons. HSO3 − is the main compound at pH = 4 and can also be oxidized and reduced with exchange of, respectively, two and four electrons. In alkaline solution sulfite is the main compound and can only be oxidized, also under exchange of two electrons. Detection limits are in the range of 4.0 ± 0.1 × 10−5 and 7.5 ± 0.1 × 10−5 mol L−1, dependent of pH and of the type of reaction (oxidation or reduction) used.
- Full Text:
- Date Issued: 2002
- Authors: Thamae, Mamothibe , Westbroek, Philippe , Nyokong, Tebello
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/304786 , vital:58490 , xlink:href="https://doi.org/10.1007/s00604-002-0914-8"
- Description: The electrocatalytic determination of SO2 is studied as a function of pH at a glassy carbon electrode modified with iron(II)tetrasulfophthalocyanine ([Fe(II)TSPc]4−). It was found in the literature that depending on pH, SO2·xH2O, HSO3 − and/or SO3 2− are the main compounds in solution, that these compounds behave differently at the electrode surface, and that the condition of the electrode surface is stable over the entire pH-range. The use of SO2(g) or sodium sulfite as starting material did result in identical curves except in the pH range from 7.5–9.0. A possible explanation could be given by proposing that SO2·xH2O is very unstable in the presence of SO3 2−. In strongly acidic medium, SO2·xH2O is the main compound, which can be oxidized as well as reduced with exchange of two electrons. HSO3 − is the main compound at pH = 4 and can also be oxidized and reduced with exchange of, respectively, two and four electrons. In alkaline solution sulfite is the main compound and can only be oxidized, also under exchange of two electrons. Detection limits are in the range of 4.0 ± 0.1 × 10−5 and 7.5 ± 0.1 × 10−5 mol L−1, dependent of pH and of the type of reaction (oxidation or reduction) used.
- Full Text:
- Date Issued: 2002
Voltammetric detection of vitamin B1 at carbon paste electrodes and its determination in tablets
- Oni, Joshua, Westbroek, Philippe, Nyokong, Tebello
- Authors: Oni, Joshua , Westbroek, Philippe , Nyokong, Tebello
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289692 , vital:56663 , xlink:href="https://doi.org/10.1002/1521-4109(200209)14"
- Description: The voltammetric behavior of vitamin B1 in alkaline medium at carbon paste electrode (CPE) is discussed. A method based on cyclic voltammetry for the determination of vitamin B1 at carbon paste electrode modified with manganese phthalocyanine (MnPc-CPE) is presented. In pH 10 buffer, the modified electrode showed catalytic activity towards the oxidation of vitamin B1 by considerably increasing the oxidation current of one of the observed waves compared to the oxidation current obtained at an unmodified electrode. The modified electrode was stable towards the determination of vitamin B1 compared to the unmodified electrode that is completely poisoned after a few scans. A linear relationship between the oxidation current and the concentration of vitamin B1 in solution was observed. The detection limit for vitamin B1 at the modified electrode was of the order of 10−5 mol dm−3. Commercial vitamin B1 tablets were analyzed using the modified electrodes.
- Full Text:
- Date Issued: 2002
- Authors: Oni, Joshua , Westbroek, Philippe , Nyokong, Tebello
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289692 , vital:56663 , xlink:href="https://doi.org/10.1002/1521-4109(200209)14"
- Description: The voltammetric behavior of vitamin B1 in alkaline medium at carbon paste electrode (CPE) is discussed. A method based on cyclic voltammetry for the determination of vitamin B1 at carbon paste electrode modified with manganese phthalocyanine (MnPc-CPE) is presented. In pH 10 buffer, the modified electrode showed catalytic activity towards the oxidation of vitamin B1 by considerably increasing the oxidation current of one of the observed waves compared to the oxidation current obtained at an unmodified electrode. The modified electrode was stable towards the determination of vitamin B1 compared to the unmodified electrode that is completely poisoned after a few scans. A linear relationship between the oxidation current and the concentration of vitamin B1 in solution was observed. The detection limit for vitamin B1 at the modified electrode was of the order of 10−5 mol dm−3. Commercial vitamin B1 tablets were analyzed using the modified electrodes.
- Full Text:
- Date Issued: 2002
Voltammetric detection of vitamin B1 at carbon paste electrodes and its determination in tablets
- Oni, Joshua, Westbroek, Philippe, Nyokong, Tebello
- Authors: Oni, Joshua , Westbroek, Philippe , Nyokong, Tebello
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289678 , vital:56662 , xlink:href="https://doi.org/10.1002/1521-4109(200209)14"
- Description: The voltammetric behavior of vitamin B1 in alkaline medium at carbon paste electrode (CPE) is discussed. A method based on cyclic voltammetry for the determination of vitamin B1 at carbon paste electrode modified with manganese phthalocyanine (MnPc-CPE) is presented. In pH 10 buffer, the modified electrode showed catalytic activity towards the oxidation of vitamin B1 by considerably increasing the oxidation current of one of the observed waves compared to the oxidation current obtained at an unmodified electrode. The modified electrode was stable towards the determination of vitamin B1 compared to the unmodified electrode that is completely poisoned after a few scans. A linear relationship between the oxidation current and the concentration of vitamin B1 in solution was observed. The detection limit for vitamin B1 at the modified electrode was of the order of 10−5 mol dm−3. Commercial vitamin B1 tablets were analyzed using the modified electrodes.
- Full Text:
- Date Issued: 2002
- Authors: Oni, Joshua , Westbroek, Philippe , Nyokong, Tebello
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289678 , vital:56662 , xlink:href="https://doi.org/10.1002/1521-4109(200209)14"
- Description: The voltammetric behavior of vitamin B1 in alkaline medium at carbon paste electrode (CPE) is discussed. A method based on cyclic voltammetry for the determination of vitamin B1 at carbon paste electrode modified with manganese phthalocyanine (MnPc-CPE) is presented. In pH 10 buffer, the modified electrode showed catalytic activity towards the oxidation of vitamin B1 by considerably increasing the oxidation current of one of the observed waves compared to the oxidation current obtained at an unmodified electrode. The modified electrode was stable towards the determination of vitamin B1 compared to the unmodified electrode that is completely poisoned after a few scans. A linear relationship between the oxidation current and the concentration of vitamin B1 in solution was observed. The detection limit for vitamin B1 at the modified electrode was of the order of 10−5 mol dm−3. Commercial vitamin B1 tablets were analyzed using the modified electrodes.
- Full Text:
- Date Issued: 2002
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