2-アミノ-3-キノキサリンチオール誘導体によるニッケルおよびコバルトの吸光光度定量

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2, 3-Quinoxalinedithiol has been known as a highly sensitive reagent for Ni and Co ions. In order to find a more superior reagent among quinoxaline drivatives, the reactions of Ni(II) and Co(II) with three quinoxalinethiol derivatives, i.e. 2-amino-3-quinoxalinethiol (AQT), 2-(N-methylamino)-3-quinoxalinethiol (MQT) and 2-(N-phenylamino)-3-quinoxalinethiol (PQT), were examined. AQT and MQT were superior to PQT in its sensitivity, stabilization of color, and effect of diverse ions. Furthermore, AQT was more sensitive for Ni(II) than 2, 3-quinoxalinedithiol. The acid dissociation constants pK1 and pK2 obtained spectrophotometrically in 50% aqueous ethanol solution are 2.86 and 8.56 for AQT and 3.12 and 9.07 for MQT, respectively. These reagents formed colored compounds with Ni(II), Cu(II), Co(II), and Pd(II). The successive formation constants (log K1, log β2) of these complexes with AQT in 50% aqueous ethanol solution were found to be 7.07, 12.04 for Ni and 5.77, 11.07 for Co, respectively. Similarly, the formation constants of MQT with Ni and Co were determined. The quantitative determination of Ni(II) and Co(II) were spectrophotometrically performed with AQT, MQT and PQT in 50% aqueous DMF solution. The recommended analytical procedure is: Two milliliter of neutral sample solution containing less than 25 μg Ni/ml or 15 μg Co/ml and 5 ml of ammonia-ammonium chloride buffer are taken in a 20 ml volumetric flask and diluted to 10 ml with water, to this solution 8 ml of DMF is added with stirring. Standing for 10 minutes, 2 ml of 0.01 M reagent DMF solution is added, and diluted to 20 ml with 50% aqueous DMF solution. Five minutes later the absorbance of the solution is measured at the analytical wavelength against blank. In the case, for example, of AQT the reddish Ni and yellowish brown Co complexes show absorption peaks at 495 nm and 428 nm. These complex formation with Ni and Co ions took place favorably in the solutions of pH 11.0 and 9.60, respectively. The coloration were rapid and stable for several hours. A linear calibration curve was obtained in the concentration ranges 0.1 to 2.5 μg Ni/ml and 0.05 to 1.5 μg Co/ml. The sensitivity expressed in 0.001 of absorbance was 0.0024 μg Ni/cm2 and 0.0016 μg Co/cm2. The molar absorption coefficient of the complex was found to be 2.4×104 liter mol-1 cm-1 for Ni and 3.78×104 liter mol-1 cm-1 for Co. Similar examinations were made to the reagents MQT and PQT with the same metal ions. The interference of diverse ions on the electronic absorbance of the complexes was slightly observed in Fe(III), Cu(II) and Pd(II).
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2-アミノ-3-キノキサリンチオール誘導体によるニッケルおよびコバルトの吸光光度定量

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