Pipat Chooto - Academia.edu (original) (raw)
Papers by Pipat Chooto
Portugaliae Electrochimica Acta, 2020
Certain N, O, S-ligating ring compounds and thioureas were investigated to understand their role ... more Certain N, O, S-ligating ring compounds and thioureas were investigated to understand their role of copper corrosion inhibition in acetonitrile. For 5 quinones under study, including xanthone, xanthene, thioxanthone, acridone and 1,4-naphthoquinone, acridone was the best inhibitor, with Cu corrosion rate of 4.495 × 10-4 mm/year, whereas 1,4naphthoquinone exhibited the lowest inhibition, due to a lower number of nitrogen groups. With the presence of sulphur, to form a stronger bond with Cu, thioureas had better inhibiting behavior than quinones. Of 4 thioureas, namely thiourea (tu), diphenylthiourea (dptu), phenylthiourea (ptu), and ethylenethiourea (etu), the fourth shows the highest inhibition-with Cu corrosion rate of 2.27 × 10-4 mm/year-and the third shows the lowest one, due to the steric effect from the phenyl group. When halide ions are present, the inhibition efficiency of thioureas decreases, due to more preferable Cu complexation to halides; the strongest copper-halide bond formation occurred by the freest iodide ion, which is consistent with the results from X-ray crystallography and electrochemistry.
International Journal of Photoenergy, 1999
Violanthrone is an anthraquinone vat dye, which is resistant to photochemical damage. Most previo... more Violanthrone is an anthraquinone vat dye, which is resistant to photochemical damage. Most previous work has concentrated on its chemiluminescence properties. In this report, electrogenerated chemiluminescence (ECL) of violanthrone has been investigated in dimethyl sulfoxide with 0.1M of tetraethylammonium bromide as electrolyte. Violanthrone luminesces in the potential range between 0.0V and-4:0V. At the sweep rate 1000 mV/s, the intensity of the violanthrone ECL is about 2% of that of tris(2,2′-bipyridine) ruthenium(II) ion under the same conditions. It was found that bromine was also produced during the ex- periment, leading to the conclusion that the luminescence arises from the reaction between radical anion of violanthrone and molecular bromine. The mechanism is discussed in detail.
Annals of Chemical Science Research, 2020
There are a large variety of factors that affect the amount of the metal of interest in the seedl... more There are a large variety of factors that affect the amount of the metal of interest in the seedlings. Surely, the first is the types and states of the metal itself. This includes different types of oxidation states due to the fact that most metals, in particular transition metals, have various oxidation numbers which of course exhibits a wide range of behaviors and toxicity. Furthermore, accompanying anions also have subtle influence on the metal concentrations in rice seedlings, mainly due to the uptake mechanisms. The next parameters should involve rice growing conditions covering periods of time, in other words, the number of days of growing, the types of nutrients or fertilizers, the methods of growing, species of rice or even the weather and environment conditions. These sophisticated parameters make the studies of
![Research paper thumbnail of The formation, characterization, and reactivity of the oxene adduct of [tetrakis(2,6-dichlorophenyl)porphinato]iron(III) perchlorate in acetonitrile. Model for the reactive intermediate of cytochrome P-450](https://a.academia-assets.com/images/blank-paper.jpg)
](Journal of the American Chemical Society, 1988
Annals of Chemical Science Research, 2019
Recent cases of casualty of workers in rubber latex factories due to hydrogen sulfide call for ur... more Recent cases of casualty of workers in rubber latex factories due to hydrogen sulfide call for urgent attention to better understanding, prevention of damages in working and living in risky environments, and promotion of public and labor awareness. Specific responsible organization here is the subcontractor of latex factories. H 2 S characteristics, sources and symptoms from exposure are emphasized. Proper practice should be followed strictly along with better cooperation among experts for the main objective in saving lives and greater safety in living and working.
Annals of Chemical Science Research, 2019
Heavy metals (HMs) have caused several problems for all living things on earth so far [1]. They d... more Heavy metals (HMs) have caused several problems for all living things on earth so far [1]. They do have both beneficial and harmful effects. Some of them in specific concentrations, oxidation numbers and forms are essential to the body of living things whereas others can be deleterious. HMs have been well known for a long time to play important roles in a number of samples especially environment and food. The greater role they have in everyday life, the greater the need for monitoring their concentrations. Several techniques have been developed to gain better figure of merits and advantages. And it would be rewarding if those techniques are able to analyze HMs simultaneously and onsite, especially for environmental analysis. Normally in standard metal ion analysis, the techniques require costly and sophisticated instruments, not to mention sample preparation. However, the main advantages of these techniques include limit of detection and analytical performance [2]. In the case that these characteristics are not the top priority compared to capability of simultaneous analysis, then electrochemical methods become very attractive and outstanding.
Journal of Electrochemical Science and Engineering, 2019
Mesoporous silica nanoparticles and chitosan were combined with ex-situ bismuth film modified gla... more Mesoporous silica nanoparticles and chitosan were combined with ex-situ bismuth film modified glassy carbon electrode (NanoSiO2-CTS/BiFE) for simultaneous determination of Pb(II) and Cd(II) in HCl/KCl pH 2.2. Differential pulse anodic stripping voltammetry (DPASV) measurements, based on formation of ion-associates between chlorocomplexes and protonated amino groups (-NH3 +) of chitosan at the electrode surface, were explored. Under optimum conditions, the linear correlation coefficient was 0.998 for both Pb(II) and Cd(II) after 240 s of deposition time. The limits of detection (LOD) and quantification (LOQ) were
Voltammetry, 2019
Cyclic voltammetry is a versatile method for scientific investigation and innovation due to the f... more Cyclic voltammetry is a versatile method for scientific investigation and innovation due to the fact that most processes involve electron transfer, which makes them be able to be monitored by this technique. Its uses cover characterization, synthesis, mechanisms, and analysis. In all applications, the technique can work well with a large variety of compounds including organic, inorganic, polymer, films, and semiconductors, among others. Furthermore, the method operates satisfactorily whether in a direct or an indirect approach. It can be considered to be an essential part at the very beginning that leads further to the grand project. As an analytical tool, it plays an important role in not only chemistry but also other involving areas. This review sheds the light on the way the technique proves to become one of the important instruments in research, development, and application labs.
Journal of Molecular Structure, 2018
Syntheses, crystal structures and Hirshfeld surface analysis of a coordination polymer of Cu(II) ... more Syntheses, crystal structures and Hirshfeld surface analysis of a coordination polymer of Cu(II) chlorido and a tris-octahedral complex of Ni(II) containing isonicotinoylhydrazone blockers,
Journal of Applied Polymer Science, 2007
A molecularly trichloroacetic acid (TCAA) imprinted non-crosslinked polypyrole (TCAA-MIPpy) has b... more A molecularly trichloroacetic acid (TCAA) imprinted non-crosslinked polypyrole (TCAA-MIPpy) has been successfully prepared and evaluated in its properties for both piezoelectric quartz crystal microbalance (QCM) and electrochemical means of detection, and application of such sensors for determination of haloacetic acid concentrations in water. Haloacetic acid selectivity was demonstrated in gravimetric or in electrochemical sensors via either cyclic voltammetric or interdigitated conductometric (IDC) analyses studies upon comparison with nonimprinted polypyrrole and TCAAimprinted polypyrrole. The measurement results with all these systems revealed that the prepared molecularly imprinted polymer can recognize TCAA well from structurally similar compounds. The TCAA-MIPpy incorporated with only the IDC transduction system produced the specific signal for TCAA detection in aqueous environment, which is useful for the quantifying TCAA disinfection by-product in water. The analytical application for determination of TCAA in real-life samples was readily achieved with the incorporation of TCAA-MIPpy in the IDC analysis system, the results revealing the high sensitivity and selectivity of the method.
Comments on Inorganic Chemistry, 1990
The electron-transfer oxidation-reduction chemistry for meso-tetrakis(2,6-dichlorophenyl)porphine... more The electron-transfer oxidation-reduction chemistry for meso-tetrakis(2,6-dichlorophenyl)porphine [ (C k TPP)Hz] and its metal complexes [ (C&TPP)M M = Mn, Fe, Co, Ni, Cu, Ag, and Zn] has been characterized by cyclic voltammetry and controlled-potential electrolysis. Electron spin resonance and magnetic measurements confiim that the cation radicals of (C&TPP)Hz, (C&TPP)Zn, and (C&TPP)Ni are ligandcentered, that the spin density for (C&TPP)Cu and (C&TPP)Ag is mainly within the porphyrin ring with three metal-nitrogen covalent bonds, and that the spin density for (C&TPP)Co' is localized on the metal. On the basis of these measurements electron transfer occurs within the porphyrin ring and the metalporphyrin bonding consists of covalent u bonds between d%p valence electrons of neutral metal and pyrrole p electrons of the porphyrin. The (C&TPP)Fem(ClOJ and (C&TPP)MnWlO,) complexes form oxygen-atom adducts ['P+FeW=O and P+MnV=O] with metal-xygen bond energies (-AGBF) of 46 and 37 kcal, respectively, which are reduced to PFew=O and PMnTV=O with M=O bond energies of 67 and 87 kcal, respectively.
Applications of the Voltammetry, 2017
Due to all the advantages of low cost, speed, and simplicity, electrochemistry has always represe... more Due to all the advantages of low cost, speed, and simplicity, electrochemistry has always represented a perfect choice to be selected in quantitative analysis particularly in the case of metal ions but with the drawback of specificity and sensitivity. With the arrival of nanomaterials, the problem of sensitivity and limit of detection has been overcome and a great variety of applications of electrochemistry especially in trace analysis are highlighted. Layers of materials can be arranged and manipulated to make the methods more specific to targeting analytes The opportunity is there for both older and newer methods to be beneficial in a large number of applications with superb analytical performance. This knowledge of modified electrodes can inspire newer and greater innovative applications of electrochemistry with the promising extension to other areas under current interests.
Lead determination in canned food by square-wave adsorptive cathodic stripping voltammetry
The complexes between copper(I) halides and N,N-diphenylthiourea have been investigated by cyclic... more The complexes between copper(I) halides and N,N-diphenylthiourea have been investigated by cyclic voltammetry to compare their structure and behaviour in solid state with those in solution. The halides under investigation include chloride, bromide, and iodide. Chloride and bromide complexes did not show the redox reaction, suggesting that they formed the strongest bond with the metal and hence the oxidation was inhibited. In contrast, iodide behaved differently because of the two peaks of halide and trihalide oxidations. One peak disappeared, leaving the other halide-oxidized peak shifted to a more positive voltage due to the bonding with the metal. In solution, all complexes of N,N-diphenylthiourea were derived from the oxidation process and exhibited oxidation potentials shifted to positive values.
Scienceasia, 2010
A simple and rapid method to determine traces of lead in the Hatyai city tap water by square wave... more A simple and rapid method to determine traces of lead in the Hatyai city tap water by square wave anodic stripping voltammetry with boron-doped diamond (BDD) electrode has been studied. The parameters in the preconcentration steps studied included electrolyte influences, pH, concentrations, and volumes. Effective preconcentration of trace lead was achieved at pH 1.26. The appropriate electrolyte was found to be 0.2 M potassium nitrate (KNO3) in 0.05 M nitric acid (HNO3) to make all lead ionic. By scanning potential in the negative direction, the stripping peak was obtained at 0.460 V. Instrumental parameters including deposition potential, deposition time, scan rate, modulation amplitude, and equilibration time were optimized. The detection limit was found to be 0.3 µg/l. The accuracy was verified by analysing the standard reference material. Several interfering ions were studied and it was found that the method was not significantly affected by these coexisting ions and can be appl...
Lead is known as a toxic metal for human health and used in many industries. For instance, it is ... more Lead is known as a toxic metal for human health and used in many industries. For instance, it is frequently used as a material for plumbing systems in drinking water cooler. Another typical materials containing lead is glaze which is a thin layer of liquid put on a piece of bowl or some ceremicware. Determination of lead amount leached from these samples is necessary and this could raise awareness of lead toxicity to consumers. Simple on-line spectrophotometric system for the determination of lead at trace level with on-line preconcentration step using Amberlite IR-120 as a sorbent packed in a minicolumn was developed. It is based on lead-4-(2-Pyridylazo)-resorcinol (PAR) complex formation to be detected spectrophotometrically at 519 nm. Under the optimal conditions, the linear range of 70-1000 µg l-1 with a correlation coefficient (R2) of 0.9998 was obtained. The limit of detection, LOD (based on 3Sx/y/m) of 55 µg l-1 and the relative standard deviation (RSD) within 5% (at 70 and 5...
The complexes between copper(I) halides and N,N 0 -diphenylthiourea have been investigated by cyc... more The complexes between copper(I) halides and N,N 0 -diphenylthiourea have been investigated by cyclic voltammetry to compare their structure and behaviour in solid state with those in solution. The halides under investigation include chloride, bromide, and iodide. Chloride and bromide complexes did not show the redox reaction, suggesting that they formed the strongest bond with the metal and hence the oxidation was inhibited. In contrast, iodide behaved differently because of the two peaks of halide and trihalide oxidations. One peak disappeared, leaving the other halide-oxidized peak shifted to a more positive voltage due to the bonding with the metal. In solution, all complexes of N,N 0 -diphenylthiourea were derived from the oxidation process and exhibited oxidation potentials shifted to positive values.
ScienceAsia, 2017
A simple method for determination of copper contents in natural rubber (NR) latex based on the co... more A simple method for determination of copper contents in natural rubber (NR) latex based on the complex formation between Cu(II) and zinc diethyldithiocarbamate (Zn(II)-DDTC) and extraction with dichloromethane followed by visible spectrophotometry at 435 nm was developed. A low-cost wet digestion system for NR latex was adopted by digesting a sample in a Pyrex tube with the a mixture of concentrated H 2 SO 4 and concentrated HNO 3 at 180°C. Under the optimum conditions, the linear range of 0.1-4.0 mg/l (R 2 > 0.99), the limit of detection and the limit of quantification were 0.0356 and 0.1188 mg/l, respectively, the intra-day (n = 10) and inter-day (n = 6) relative standard deviations were 0.4-3.2 and 0.8-3.4%, respectively, and recoveries of 92-101% were obtained. Fe(III), Mn(II), and Zn(II) did not interfere with the tolerance limit of 9.0, 9.0, and more than 500 mg/l, respectively, which are higher than their usual concentrations in latex. The method was applied to copper determination in a concentrated latex sample prepared from field latex samples by centrifugation. The copper content was found to be 6.8-7.0 mg/kg (on total solids content) and copper content in the field NR latex sample was 16.6-23.8 mg/kg (on total solids content). No difference was observed between the proposed method and ICP-OES as well as between the proposed digestion and Kjeldahl digestion.
ScienceAsia, 2017
A boron-doped diamond electrode modified by 0.5 mM 4-aminomethyl benzoic acid was used for electr... more A boron-doped diamond electrode modified by 0.5 mM 4-aminomethyl benzoic acid was used for electrochemical determination of Cd 2+ in tap water samples by anodic stripping voltammetry. This method is based on the electrochemical reduction of 4-aminomethyl benzoic acid on the electrode followed by the determination of Cd 2+ with a single well-defined reduction peak at −0.72 V versus Ag/AgCl in acetate buffer solutions at pH 6.0. Optimal conditions were established with respect to electrode pretreatment, time accumulation, potential accumulation, scan rate, and pH. Accurate (r 2 = 0.9989, n = 6) calibration curves were obtained for Cd 2+ concentrations ranging between 2 ppb and 50 ppb. Other dissolved metals (Ca, Mg, Zn, Mn, Fe, Cu, Al, Co, Pb, and Ni) have no interference on the Cd 2+ calibration curves. The achieved detection limit was 0.2 ppb. High accuracy and reproducibility of the results as well as excellent stability of the electrode material proves superb capabilities of this Cd 2+ detection system. Recovery in the range of 97-102% further confirmed the usefulness of the proposed method to analyse Cd 2+ in tap water samples. The results with SRM1640 were in good agreement with those by inductively coupled plasma optical emission spectrometry.
ScienceAsia, 2015
A sample preparation method has been developed to detect cadmium and lead in commercial frozen se... more A sample preparation method has been developed to detect cadmium and lead in commercial frozen seafood samples. After being digested with concentrated HNO 3 in a closed polypropylene vessel, the clear sample solution was separated and preconcentrated by solid phase extraction using octadecyl silica membrane discs modified with 8-hydroxyquinoline prior to determination by graphite furnace atomic absorption spectrometry (GFAAS). The preconcentration conditions including pH, ligand quantity, eluent concentration, and volume were found to be effective with 10.0 mg of 8-hydroxyquinoline in 2.0 ml ethanol and pH 6.0. The retained cadmium and lead were efficiently eluted with 5.0 ml of 1.0 M HNO 3 and determined by GFAAS. The detection limits for cadmium and lead were 0.073 µg/l and 0.332 µg/l, respectively. The proposed method was tested with the certified reference material, DORM-2 (Dogfish muscle), with good agreement. The recoveries were found to be 100-103% (n = 4) for Cd and 92-108% (n = 5) for Pb with relative standard deviation (n = 5) of 3% for Cd and 4% for Pb. The extraction was found to be unaffected by coexisting ions. The method was applied satisfactorily to the seafood samples and trace levels of cadmium and lead were found.
Portugaliae Electrochimica Acta, 2020
Certain N, O, S-ligating ring compounds and thioureas were investigated to understand their role ... more Certain N, O, S-ligating ring compounds and thioureas were investigated to understand their role of copper corrosion inhibition in acetonitrile. For 5 quinones under study, including xanthone, xanthene, thioxanthone, acridone and 1,4-naphthoquinone, acridone was the best inhibitor, with Cu corrosion rate of 4.495 × 10-4 mm/year, whereas 1,4naphthoquinone exhibited the lowest inhibition, due to a lower number of nitrogen groups. With the presence of sulphur, to form a stronger bond with Cu, thioureas had better inhibiting behavior than quinones. Of 4 thioureas, namely thiourea (tu), diphenylthiourea (dptu), phenylthiourea (ptu), and ethylenethiourea (etu), the fourth shows the highest inhibition-with Cu corrosion rate of 2.27 × 10-4 mm/year-and the third shows the lowest one, due to the steric effect from the phenyl group. When halide ions are present, the inhibition efficiency of thioureas decreases, due to more preferable Cu complexation to halides; the strongest copper-halide bond formation occurred by the freest iodide ion, which is consistent with the results from X-ray crystallography and electrochemistry.
International Journal of Photoenergy, 1999
Violanthrone is an anthraquinone vat dye, which is resistant to photochemical damage. Most previo... more Violanthrone is an anthraquinone vat dye, which is resistant to photochemical damage. Most previous work has concentrated on its chemiluminescence properties. In this report, electrogenerated chemiluminescence (ECL) of violanthrone has been investigated in dimethyl sulfoxide with 0.1M of tetraethylammonium bromide as electrolyte. Violanthrone luminesces in the potential range between 0.0V and-4:0V. At the sweep rate 1000 mV/s, the intensity of the violanthrone ECL is about 2% of that of tris(2,2′-bipyridine) ruthenium(II) ion under the same conditions. It was found that bromine was also produced during the ex- periment, leading to the conclusion that the luminescence arises from the reaction between radical anion of violanthrone and molecular bromine. The mechanism is discussed in detail.
Annals of Chemical Science Research, 2020
There are a large variety of factors that affect the amount of the metal of interest in the seedl... more There are a large variety of factors that affect the amount of the metal of interest in the seedlings. Surely, the first is the types and states of the metal itself. This includes different types of oxidation states due to the fact that most metals, in particular transition metals, have various oxidation numbers which of course exhibits a wide range of behaviors and toxicity. Furthermore, accompanying anions also have subtle influence on the metal concentrations in rice seedlings, mainly due to the uptake mechanisms. The next parameters should involve rice growing conditions covering periods of time, in other words, the number of days of growing, the types of nutrients or fertilizers, the methods of growing, species of rice or even the weather and environment conditions. These sophisticated parameters make the studies of
Journal of the American Chemical Society, 1988
Annals of Chemical Science Research, 2019
Recent cases of casualty of workers in rubber latex factories due to hydrogen sulfide call for ur... more Recent cases of casualty of workers in rubber latex factories due to hydrogen sulfide call for urgent attention to better understanding, prevention of damages in working and living in risky environments, and promotion of public and labor awareness. Specific responsible organization here is the subcontractor of latex factories. H 2 S characteristics, sources and symptoms from exposure are emphasized. Proper practice should be followed strictly along with better cooperation among experts for the main objective in saving lives and greater safety in living and working.
Annals of Chemical Science Research, 2019
Heavy metals (HMs) have caused several problems for all living things on earth so far [1]. They d... more Heavy metals (HMs) have caused several problems for all living things on earth so far [1]. They do have both beneficial and harmful effects. Some of them in specific concentrations, oxidation numbers and forms are essential to the body of living things whereas others can be deleterious. HMs have been well known for a long time to play important roles in a number of samples especially environment and food. The greater role they have in everyday life, the greater the need for monitoring their concentrations. Several techniques have been developed to gain better figure of merits and advantages. And it would be rewarding if those techniques are able to analyze HMs simultaneously and onsite, especially for environmental analysis. Normally in standard metal ion analysis, the techniques require costly and sophisticated instruments, not to mention sample preparation. However, the main advantages of these techniques include limit of detection and analytical performance [2]. In the case that these characteristics are not the top priority compared to capability of simultaneous analysis, then electrochemical methods become very attractive and outstanding.
Journal of Electrochemical Science and Engineering, 2019
Mesoporous silica nanoparticles and chitosan were combined with ex-situ bismuth film modified gla... more Mesoporous silica nanoparticles and chitosan were combined with ex-situ bismuth film modified glassy carbon electrode (NanoSiO2-CTS/BiFE) for simultaneous determination of Pb(II) and Cd(II) in HCl/KCl pH 2.2. Differential pulse anodic stripping voltammetry (DPASV) measurements, based on formation of ion-associates between chlorocomplexes and protonated amino groups (-NH3 +) of chitosan at the electrode surface, were explored. Under optimum conditions, the linear correlation coefficient was 0.998 for both Pb(II) and Cd(II) after 240 s of deposition time. The limits of detection (LOD) and quantification (LOQ) were
Voltammetry, 2019
Cyclic voltammetry is a versatile method for scientific investigation and innovation due to the f... more Cyclic voltammetry is a versatile method for scientific investigation and innovation due to the fact that most processes involve electron transfer, which makes them be able to be monitored by this technique. Its uses cover characterization, synthesis, mechanisms, and analysis. In all applications, the technique can work well with a large variety of compounds including organic, inorganic, polymer, films, and semiconductors, among others. Furthermore, the method operates satisfactorily whether in a direct or an indirect approach. It can be considered to be an essential part at the very beginning that leads further to the grand project. As an analytical tool, it plays an important role in not only chemistry but also other involving areas. This review sheds the light on the way the technique proves to become one of the important instruments in research, development, and application labs.
Journal of Molecular Structure, 2018
Syntheses, crystal structures and Hirshfeld surface analysis of a coordination polymer of Cu(II) ... more Syntheses, crystal structures and Hirshfeld surface analysis of a coordination polymer of Cu(II) chlorido and a tris-octahedral complex of Ni(II) containing isonicotinoylhydrazone blockers,
Journal of Applied Polymer Science, 2007
A molecularly trichloroacetic acid (TCAA) imprinted non-crosslinked polypyrole (TCAA-MIPpy) has b... more A molecularly trichloroacetic acid (TCAA) imprinted non-crosslinked polypyrole (TCAA-MIPpy) has been successfully prepared and evaluated in its properties for both piezoelectric quartz crystal microbalance (QCM) and electrochemical means of detection, and application of such sensors for determination of haloacetic acid concentrations in water. Haloacetic acid selectivity was demonstrated in gravimetric or in electrochemical sensors via either cyclic voltammetric or interdigitated conductometric (IDC) analyses studies upon comparison with nonimprinted polypyrrole and TCAAimprinted polypyrrole. The measurement results with all these systems revealed that the prepared molecularly imprinted polymer can recognize TCAA well from structurally similar compounds. The TCAA-MIPpy incorporated with only the IDC transduction system produced the specific signal for TCAA detection in aqueous environment, which is useful for the quantifying TCAA disinfection by-product in water. The analytical application for determination of TCAA in real-life samples was readily achieved with the incorporation of TCAA-MIPpy in the IDC analysis system, the results revealing the high sensitivity and selectivity of the method.
Comments on Inorganic Chemistry, 1990
The electron-transfer oxidation-reduction chemistry for meso-tetrakis(2,6-dichlorophenyl)porphine... more The electron-transfer oxidation-reduction chemistry for meso-tetrakis(2,6-dichlorophenyl)porphine [ (C k TPP)Hz] and its metal complexes [ (C&TPP)M M = Mn, Fe, Co, Ni, Cu, Ag, and Zn] has been characterized by cyclic voltammetry and controlled-potential electrolysis. Electron spin resonance and magnetic measurements confiim that the cation radicals of (C&TPP)Hz, (C&TPP)Zn, and (C&TPP)Ni are ligandcentered, that the spin density for (C&TPP)Cu and (C&TPP)Ag is mainly within the porphyrin ring with three metal-nitrogen covalent bonds, and that the spin density for (C&TPP)Co' is localized on the metal. On the basis of these measurements electron transfer occurs within the porphyrin ring and the metalporphyrin bonding consists of covalent u bonds between d%p valence electrons of neutral metal and pyrrole p electrons of the porphyrin. The (C&TPP)Fem(ClOJ and (C&TPP)MnWlO,) complexes form oxygen-atom adducts ['P+FeW=O and P+MnV=O] with metal-xygen bond energies (-AGBF) of 46 and 37 kcal, respectively, which are reduced to PFew=O and PMnTV=O with M=O bond energies of 67 and 87 kcal, respectively.
Applications of the Voltammetry, 2017
Due to all the advantages of low cost, speed, and simplicity, electrochemistry has always represe... more Due to all the advantages of low cost, speed, and simplicity, electrochemistry has always represented a perfect choice to be selected in quantitative analysis particularly in the case of metal ions but with the drawback of specificity and sensitivity. With the arrival of nanomaterials, the problem of sensitivity and limit of detection has been overcome and a great variety of applications of electrochemistry especially in trace analysis are highlighted. Layers of materials can be arranged and manipulated to make the methods more specific to targeting analytes The opportunity is there for both older and newer methods to be beneficial in a large number of applications with superb analytical performance. This knowledge of modified electrodes can inspire newer and greater innovative applications of electrochemistry with the promising extension to other areas under current interests.
Lead determination in canned food by square-wave adsorptive cathodic stripping voltammetry
The complexes between copper(I) halides and N,N-diphenylthiourea have been investigated by cyclic... more The complexes between copper(I) halides and N,N-diphenylthiourea have been investigated by cyclic voltammetry to compare their structure and behaviour in solid state with those in solution. The halides under investigation include chloride, bromide, and iodide. Chloride and bromide complexes did not show the redox reaction, suggesting that they formed the strongest bond with the metal and hence the oxidation was inhibited. In contrast, iodide behaved differently because of the two peaks of halide and trihalide oxidations. One peak disappeared, leaving the other halide-oxidized peak shifted to a more positive voltage due to the bonding with the metal. In solution, all complexes of N,N-diphenylthiourea were derived from the oxidation process and exhibited oxidation potentials shifted to positive values.
Scienceasia, 2010
A simple and rapid method to determine traces of lead in the Hatyai city tap water by square wave... more A simple and rapid method to determine traces of lead in the Hatyai city tap water by square wave anodic stripping voltammetry with boron-doped diamond (BDD) electrode has been studied. The parameters in the preconcentration steps studied included electrolyte influences, pH, concentrations, and volumes. Effective preconcentration of trace lead was achieved at pH 1.26. The appropriate electrolyte was found to be 0.2 M potassium nitrate (KNO3) in 0.05 M nitric acid (HNO3) to make all lead ionic. By scanning potential in the negative direction, the stripping peak was obtained at 0.460 V. Instrumental parameters including deposition potential, deposition time, scan rate, modulation amplitude, and equilibration time were optimized. The detection limit was found to be 0.3 µg/l. The accuracy was verified by analysing the standard reference material. Several interfering ions were studied and it was found that the method was not significantly affected by these coexisting ions and can be appl...
Lead is known as a toxic metal for human health and used in many industries. For instance, it is ... more Lead is known as a toxic metal for human health and used in many industries. For instance, it is frequently used as a material for plumbing systems in drinking water cooler. Another typical materials containing lead is glaze which is a thin layer of liquid put on a piece of bowl or some ceremicware. Determination of lead amount leached from these samples is necessary and this could raise awareness of lead toxicity to consumers. Simple on-line spectrophotometric system for the determination of lead at trace level with on-line preconcentration step using Amberlite IR-120 as a sorbent packed in a minicolumn was developed. It is based on lead-4-(2-Pyridylazo)-resorcinol (PAR) complex formation to be detected spectrophotometrically at 519 nm. Under the optimal conditions, the linear range of 70-1000 µg l-1 with a correlation coefficient (R2) of 0.9998 was obtained. The limit of detection, LOD (based on 3Sx/y/m) of 55 µg l-1 and the relative standard deviation (RSD) within 5% (at 70 and 5...
The complexes between copper(I) halides and N,N 0 -diphenylthiourea have been investigated by cyc... more The complexes between copper(I) halides and N,N 0 -diphenylthiourea have been investigated by cyclic voltammetry to compare their structure and behaviour in solid state with those in solution. The halides under investigation include chloride, bromide, and iodide. Chloride and bromide complexes did not show the redox reaction, suggesting that they formed the strongest bond with the metal and hence the oxidation was inhibited. In contrast, iodide behaved differently because of the two peaks of halide and trihalide oxidations. One peak disappeared, leaving the other halide-oxidized peak shifted to a more positive voltage due to the bonding with the metal. In solution, all complexes of N,N 0 -diphenylthiourea were derived from the oxidation process and exhibited oxidation potentials shifted to positive values.
ScienceAsia, 2017
A simple method for determination of copper contents in natural rubber (NR) latex based on the co... more A simple method for determination of copper contents in natural rubber (NR) latex based on the complex formation between Cu(II) and zinc diethyldithiocarbamate (Zn(II)-DDTC) and extraction with dichloromethane followed by visible spectrophotometry at 435 nm was developed. A low-cost wet digestion system for NR latex was adopted by digesting a sample in a Pyrex tube with the a mixture of concentrated H 2 SO 4 and concentrated HNO 3 at 180°C. Under the optimum conditions, the linear range of 0.1-4.0 mg/l (R 2 > 0.99), the limit of detection and the limit of quantification were 0.0356 and 0.1188 mg/l, respectively, the intra-day (n = 10) and inter-day (n = 6) relative standard deviations were 0.4-3.2 and 0.8-3.4%, respectively, and recoveries of 92-101% were obtained. Fe(III), Mn(II), and Zn(II) did not interfere with the tolerance limit of 9.0, 9.0, and more than 500 mg/l, respectively, which are higher than their usual concentrations in latex. The method was applied to copper determination in a concentrated latex sample prepared from field latex samples by centrifugation. The copper content was found to be 6.8-7.0 mg/kg (on total solids content) and copper content in the field NR latex sample was 16.6-23.8 mg/kg (on total solids content). No difference was observed between the proposed method and ICP-OES as well as between the proposed digestion and Kjeldahl digestion.
ScienceAsia, 2017
A boron-doped diamond electrode modified by 0.5 mM 4-aminomethyl benzoic acid was used for electr... more A boron-doped diamond electrode modified by 0.5 mM 4-aminomethyl benzoic acid was used for electrochemical determination of Cd 2+ in tap water samples by anodic stripping voltammetry. This method is based on the electrochemical reduction of 4-aminomethyl benzoic acid on the electrode followed by the determination of Cd 2+ with a single well-defined reduction peak at −0.72 V versus Ag/AgCl in acetate buffer solutions at pH 6.0. Optimal conditions were established with respect to electrode pretreatment, time accumulation, potential accumulation, scan rate, and pH. Accurate (r 2 = 0.9989, n = 6) calibration curves were obtained for Cd 2+ concentrations ranging between 2 ppb and 50 ppb. Other dissolved metals (Ca, Mg, Zn, Mn, Fe, Cu, Al, Co, Pb, and Ni) have no interference on the Cd 2+ calibration curves. The achieved detection limit was 0.2 ppb. High accuracy and reproducibility of the results as well as excellent stability of the electrode material proves superb capabilities of this Cd 2+ detection system. Recovery in the range of 97-102% further confirmed the usefulness of the proposed method to analyse Cd 2+ in tap water samples. The results with SRM1640 were in good agreement with those by inductively coupled plasma optical emission spectrometry.
ScienceAsia, 2015
A sample preparation method has been developed to detect cadmium and lead in commercial frozen se... more A sample preparation method has been developed to detect cadmium and lead in commercial frozen seafood samples. After being digested with concentrated HNO 3 in a closed polypropylene vessel, the clear sample solution was separated and preconcentrated by solid phase extraction using octadecyl silica membrane discs modified with 8-hydroxyquinoline prior to determination by graphite furnace atomic absorption spectrometry (GFAAS). The preconcentration conditions including pH, ligand quantity, eluent concentration, and volume were found to be effective with 10.0 mg of 8-hydroxyquinoline in 2.0 ml ethanol and pH 6.0. The retained cadmium and lead were efficiently eluted with 5.0 ml of 1.0 M HNO 3 and determined by GFAAS. The detection limits for cadmium and lead were 0.073 µg/l and 0.332 µg/l, respectively. The proposed method was tested with the certified reference material, DORM-2 (Dogfish muscle), with good agreement. The recoveries were found to be 100-103% (n = 4) for Cd and 92-108% (n = 5) for Pb with relative standard deviation (n = 5) of 3% for Cd and 4% for Pb. The extraction was found to be unaffected by coexisting ions. The method was applied satisfactorily to the seafood samples and trace levels of cadmium and lead were found.