Development of an ultra-sensitive electrochemical method for the determination of phosphate ion with molecular fractionation and adsorptive collection

为建立超灵敏的测定磷酸根离子的方法，研究了分子分离-吸附伏安法。该方法的原理是：(1)在磷酸根离子溶液中加入钼离子和抗坏血酸后，用磷钼酸生成磷钼蓝；(2)用分子分级柱将磷钼蓝从同多钼蓝中分离出来；(3)将磷钼蓝分解成钼离子；(4)用钼离子吸附溶出伏安法间接测定磷酸根离子。在pH值为2的条件下，采用GS220HQ色谱柱，钼离子和抗坏血酸可以很好地分离，而磷钼蓝则不能被检测到。采用GL-W510色谱柱，可获得磷钼蓝的峰信号。在现阶段，由于峰的拖尾，响应与磷酸盐浓度不是线性的，但这一点可以通过进一步研究最佳条件来改善。3-氯-扁桃酸吸附伏安法测定钼的检出限为5 pM。该方法的灵敏度为1900nA/nM/min，钼离子的检出限为0.3 pM，磷酸根离子的检出限为0.03 pM。4-氯-扁桃酸和4-溴-扁桃酸对钼离子的灵敏测定也有良好的效果。此外，还阐明了汞电极对配位体的回馈对络合物在电极上的吸附具有重要意义。在氯酸根存在下，扁桃酸中的亲电官能团键合在芳环上，加快了催化反应的速度。对痕量金属离子的伏安形态和有机物的光解进行了研究。

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.