α-メルカプトプロピオン酸共存下のポーラログラフ法による鉛,スズ,カドミウム,インジウムの同時定量

In an acidic buffer solution containing α-mercaptopropionic acid (α-MPA) at pH higher than 2.5, tin-(IV) produces a single step reduction wave. This step is resulted from the reduction of tin(IV) to tin amalgam and is diffusion controlled.<BR>Indium(III) shows a well defined reduction wave that is diffusion controlled over the pH range between 1.5 and 6 in the presence of α-MPA. In this pH region, the reduction wave is observed to be reversible.<BR>The effect of α-MPA concentration on the limiting current of the system is determined in 0.4 M citrate buffer solution of pH 3.5. The diffusion current be comes constant when 4: 1 mole ratio of α-MPA to tin(IV) or indium(III) is reached.<BR>The limiting currents of both lead(II) and cadmium(II) are diffusion controlled and are proportional to each concentration in the presence of α-MPA.<BR>The half wave potential of tin(IV) reduction wave is about 100 mV negative than that of lead(II) in 0.4 M citrate buffer solution containing 10 mM α-MPA and 0.0015 % Triton X-100 at pH 3.5. The half wave potential of tin(IV) is shifted about 70 mV to a negative potential when pH increases one unit, while that of lead (II) is shifted about 40 mV. As a result, at the pH values higher than 3.5, lead(II) and tin(IV) can be determined simultaneously.<BR>Indium(III) is reduced at about 70 mV more negative potential than cadmium(II) in citrate buffer solution at pH 5.0.<BR>The plot of half wave potential against pH gives a straight line. Since the slope for cadmium(II) is about 36 mV/pH and that for indium(III) is about 54 mV/ pH, it is possible to determine the indium and cadmium contents from the separated waves in supporting electrolytes containing 10 mM α-MPA above pH 5.0.<BR>All of them show well developed waves and the diffusion current is proportional to the concentration of each ion in the concentration range from 10^-4 M to 10^-3 M.<BR>Copper(II) and antimony(III) are reduced at half wave potentials of -0.53 V and -0.48 V vs. SCE in 0.2 M citrate buffer solution containing 10 mM α-MPA, respectively (pH 4.13). Both copper (II) and antimony(III) must be removed from the test solution to be determined because they overlap the reduction waves of lead(II) and tin(IV).<BR>As bismuth(III) reduction wave has a half wave potential of -0.36 V vs. SCE in 0.2 M citrate buffer solution of pH 5.18, it can be separated from lead(II) wave (E_1/2 -0.52 V vs. SCE).<BR>Being applied to the determination of lead and tin in the solder, the results agree well with those by the JIS method. The limit of error is less than 2% and the results are reproducible. The time required for the analysis is about 45 minutes.