• S Abraham John

      Articles written in Journal of Chemical Sciences

    • Electrochemical behaviour of Prussian Blue at Nation coated electrode

      S Abraham John R Ramaraj

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    • Role of acidity on the electrochemistry of Prussian Blue at plain and Nation filmcoated electrodes

      S Abraham John R Ramaraj

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      Prussian Blue (PB) coated on plain platinum (Pt) shows a redox wave at 0.44V vs SCE in addition to the two usual redox waves at 0.82 and 0.12 V vs SCE when the electrodes were dipped in acidic KC1 solution. PB incorporated into Nation film-coated on Pt electrode exhibited the same behaviour even in the presence of neutral KG solution. In acidic KC1, the additional redox wave observed for PB incorporated into Nation film shifted positively to 0.39V vs SCE and the peak separation was reduced to 30mV. The observed additional redox wave for PB coated on plain Pt electrode and incorporated into Nafion film-coated Pt electrodes was assigned to the partial reduction of PB occurring due to the insertion of protons into the film. The effect of various cations on the electrochemistry of PB incorporated into Nafion film-coated electrode was also studied.

    • Selective determination of 3,4-dihydroxyphenylacetic acid in the presence of ascorbic and uric acids using polymer film modified electrode

      Palraj Kalimuthu S Abraham John

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      We report here the highly sensitive and selective electrochemical determination of 3,4-dihydroxyphenylacetic acid (DOPAC), one of the dopamine metabolites in the presence of important interferents ascorbic acid (AA) and uric acid (UA) using an ultrathin electropolymerized film of 5-amino-1,3,4-thiadiazole-2-thiol (p-ATT) modified glassy carbon (GC) electrode in 0.20M phosphate buffer solution (pH 5.0). The bare GC electrode fails to resolve the oxidation peaks of AA, DOPAC and UA in a mixture. Further, the oxidation peak potentials of them were shifted to more positive potential with decreased peak currents in the subsequent cycles. On the other hand, the p-ATT modified electrode not only separated the voltammetric signals of AA, DOPAC and UA but also enhanced their peak currents. The amperometric current response was increased linearly with increasing DOPAC concentration in the range of $4.0 \times 10^{−8}$ to $1.0 \times 10^{−5}$ M and the detection limit was found to be 150pM ($S/N =3$).

    • Fabrication of optochemical and electrochemical sensors using thin films of porphyrin and phthalocyanine derivatives

      Palanisamy Kalimuthu Arumugam Sivanesan S Abraham John

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      This paper describes the fabrication of thin films of porphyrin and metallophthalocyanine derivatives on different substrates for the optochemical detection of HCl gas and electrochemical determination of L-cysteine (CySH). Solid state gas sensor for HCl gas was fabricated by coating meso-substituted porphyrin derivatives on glass slide and examined optochemical sensing of HCl gas. The concentration of gaseous HCl was monitored from the changes in the absorbance of Soret band. Among the different porphyrin derivatives, meso-tetramesitylporphyrin (MTMP) coated film showed excellent sensitivity towards HCl and achieved a detection limit of 0.03 ppm HCl. Further, we have studied the self-assembly of 1,8,15,22-tetraaminometallophthalocyanine (4𝛼-MTAPc; M = Co and Ni) from DMF on GC electrode. The CVs for the self-assembled monolayers (SAMs) of 4𝛼-CoIITAPc and 4𝛼4-NiIITAPc show two pairs of well-defined redox couple corresponding to metal and ring. Using the 4𝛼-CoIITAPc SAM modified electrode, sensitive and selective detection of L-cysteine was demonstrated. Further, the SAM modified electrode also successfully separates the oxidation potentials of AA and CySH with a peak separation of 320mV.

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