| Research Abstract |
To establish an ultra-sensitive method for the determination of phosphate ion, molecular fractionation followed by adsorptive voltammetry was investigated. The principle of the method is; (1)production of phosphomolybdenum blue via phosphomolybdic acid after the addition of molybdenum ion and ascorbic acid to phosphate ion solution, (2)separation of phosphomolybdenum blue from isopoly molybdenum blue by HPLC with molecular fractionation column, (3)decomposition of phosphomolybdenum blue to produce molybdenum ion, (4) indirect determination of phosphate ion by adsorptive stripping voltammetric determination of molybdenum ion. At pH 2, with using a column ofGS220HQ, molybdenum ion and ascorbic acid could be separated satisfactorily, however, phosphomolybdenum blue could not be detected. With a column of GL-W510, peak signal for phosphomolybdenum blue could be obtained. At the present stage, the response is not linear to the phosphate concentration because of tailing of the peak, however, this could be improved by further investigation for optimum condition. Adsorptive voltammetric determination of molybdenum ion with 3-C1-mandelic acid give a limit of detection of 5 pM. This method has a sensitivity of 1900 nA/nM/min which shows the potentiality of a limit of detection of 0.3 pM for molybdenum ion and 0.03 pM for phosphate ion. 4-C1- and 4-Br-mandelic acids were also shown to be good for the sensitive determination of molybdenum ion. Further, it was clarified that back donation from mercury electrode to a ligand is significant for the adsorption of the complex to the electrode. Eleetrophilic functional group bonded to aromatic ring in mandelic acid enlarged the rate of catalytic reaction in the presence of chlorate ion. Investigation for voltammetric speciation of trace metal ion and photolytic decomposition of organic compound was also carried out.
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