Abstract
In order to develop new reagents for catalytic analysis of cobalt, monoazo derivatives of 1-amino-8-naphthol-3, 6-disulfonic acid having electron-attractive or -donative groups were synthesized. Relationship between the structure of dyes and sensitivity for the catalytic analysis of cobalt was investigated. By following the Hammett's law, the fading rate of almost all of the examined dyes was accelerated by substitution of electron-donative groups in the dyes. The dyes having electron-donative groups were useful as the sensitive reagents for the catalytic analysis of cobalt. Further, the optimum conditions were investigated for the determination of cobalt with the most sensitive reagent, 1-amino-8-hydroxy-7-(p-hydroxyphenylazo)-3, 6-naphthalenedisulfonic acid (p-OH) among the examined dyes. The procedure was as follows: Take a sample solution containing less than 60 ng of Co (II), add 1.5 ml of 0.1 M Tiron solution and 5 ml of 3.5×10-4 M dye solution, and dilute the solution with water to a 50 ml after adjusting pH to 10.5. Then, circulate the solution through a flow cell in order to determine the absorbance with tube pump (flow rate: 2.5 ml/min). Add 2 ml of hydrogen peroxide solution (6.2%). Read the values (A1, A6) of absorbance after 1 min and 6 min, respectively. A calibration curve was constructed by relationship between ln (A1/A6) and the concentration of cobalt. The values of ln (A1/A6) were nearly proportional up to 1.2 ppb of cobalt, and the relative standard deviation was 6.9% (n=7) at 1 ppb of cobalt.
