紫外脉冲荧光法测定高硬度地下水中铀

Determination of uranium in high-hardness groundwater by ultraviolet impulse fluorescence method

按国标GB/T6768-986推荐的紫外脉冲荧光法直接测定高硬度地下水中铀时,加入 铀荧光增强剂后溶液会变得浑浊,使得测定无法继续进行,而测定普通低硬度水样未见这种现象.实验对产生这一现象的原因进行了分析,结果表明,高硬度地下水中含量较高的钙离子与 铀荧光增强剂中的磷酸盐发生化学反应生成了磷酸钙沉淀,是导致溶液浑浊的根本原因;虽然 锾离子也会与磷酸根发生反应,但是按国标法选用的条件进行测定时不会与磷酸根反应,从而对轴的测定无影响.实验通过向被测水样中加入适量的乙二醇-双-（2-氨基乙醚）四乙酸 （EGTA ）络合剂使其与钓离子络合,即可避免由于轴荧;光增强剂的加入而导致的溶液浑浊现象,从而实现了高硬度地下水中铀的紫外脉冲荧光测定.在优化的实验条件下,方法的检出限 为0. 02 μg/L .采用紫外脉冲荧光法测定高硬度地下水实际样品,测得结果与电感耦合等离子体质谱法（ ICP-MS ）基本一致,相对标准偏差（ RSD, n =11）低于5 % ,加标回收率在99. 5 % -101 %之间.

During the direct determination of uranium in high-hardness groundwater by ultraviolet impulse fluorescence method which was recommended by national standard （GB/T 6768- 986） , the solution would be turbid after adding fluorescence intensifier of uranium and the determination was hardly conducted. However, this phenomenon was not observed for the determination of normal low-hardness water samples. The cause of this phenomenon was analyzed in this study. The results showed that the calcium ion （the content of calcium ion in high-hardness groundwater was usually high） could react with phosphates in fluo-rescence intensifier of uranium to form calcium phosphate precipitate, which was the root cause to result in turbidity. Although magnesium ion could also react with phosphate, the reaction did not occur under the selection conditions of national standard method. Therefore, it had no influence on the determination of u-ranium. In this study, proper amount of ethylene glycol-bis-（2-aminoether） acetate tetrahydrate （EGTA） was added into testing water sample for the complexation with calcium ion, avoiding the turbid phenome-non of solution after adding fluorescence intensifier of uranium. The determination method of uranium in high-hardness groundwater by ultraviolet impulse fluorescence was established. Under the optimized experimental conditions, the detection limit of method was 0. 02 μg/L. The ultraviolet impulse fluorescence method was applied to the determination of actual high-hardness groundwater samples. The found results were basically consistent with those obtained by inductively coupled plasma mass spectrometry （ICP-MS）. The relative standard deviations （RSD, n = ll） were less than 5%. The recoveries of standard addition were between 99. 5% and 101%.