淡水磷酸盐氧同位素前处理方法的优化

Optimization approach of pretreatment methods for phosphate oxygen isotopic analysis in freshwater

磷是地表水体中的关键性营养盐,在水生生态系统的物质循环与能量流动方面发挥着重要作用,研究水体中磷的来源、转化与归趋对于了解水环境的演变过程与科学保护具有重要意义.近年来,磷酸盐氧同位素(δ18 O P)技术已逐渐应用于淡水环境中磷的来源示踪与生物地球化学循环研究,其样品前处理主要沿用海水方法体系.相比而言,淡水样品中PO 3-4浓度通常较低,有机质和干扰离子含量却较高,复杂的样品前处理过程极大地制约了δ18 O P分析在淡水环境体系的广泛应用.为此,本研究针对现有海水样品δ18 O P前处理方法在地表淡水环境的适用性加以检验,并进行了三点优化改进:①将MAGIC沉淀步骤使用的MgCl 2替换为Mg(NO 3)2,避免了Cl-的干扰,减少AgCl杂质的生成;②调节生成Ag3PO4溶液pH值为8.0,保证Ag3PO4沉淀快速完全;③对Ag3PO4沉淀过程采用避光处理,降低了AgNO 3及Ag3PO4可能的光解影响,提高了Ag3PO4的纯度,使δ18 O P的测试结果更为准确.本改进方法为后续利用δ18 O P技术深入探究淡水环境中磷的生物地球化学循环与生态环境效应提供了有益的方法借鉴.

Phosphorus(P)is one of the key nutrients in surface water,and plays a vital role in the material cycle and energy flow in aquatic ecosystems.Hence,it is of great significance to explore the source,transformation,and fate in water body for understanding its evolution process and scientific protection of water environment.Recently,phosphate oxygen isotope technology(δ18 O P)has been gradually applied in tracing the P source and studying the biogeochemical cycle in freshwater environment,which most used the sample pretreatment of seawater methods.By contrast,the concentrations of PO 3-4 in freshwater samples are usually low,whereas the contents of organic matter and interference ions are high.The pretreatment complexity restricted the extensive application ofδ18 O P analysis in freshwater ecosystems.This study examined the applicability of the existing pretreatment methods of seawater sample in surface freshwater environment,and further carried out three optimization improvements:①We replaced MgCl 2 solution with Mg(NO 3)2 solution in the MAGIC precipitation step to avoid the interference of Cl-and the impurities of AgCl.②The solution pH value of Ag3PO4 precipitation was adjusted to 8.0 to ensure the rapid and complete precipitation.③Possible photolysis effects of AgNO 3 and Ag3PO4 were inhibited by using light avoidance.This modification improved the purity of Ag3PO4,and attained more accurateδ18 O P results.The present method gives a valuable reference to further study of the biogeochemical cycle and eco-effects of P in freshwater environment usingδ18 O P analysis.