湖泊水体悬浮物中痕量砷的测定方法

重金属在悬浮物和水相中的分配是水体重金属形态研究的重要组成部分,对于追踪水体中重金属元素的来源、迁移转化规律以及重金属生态与健康效应具有重要意义.水中砷元素以其极强的毒性严重危害人类的健康,已越来越引起政府和社会的广泛关注.然而,目前关于痕量悬浮物中砷测定的前处理过程及室内分析的方法与质量控制的叙述不够详尽,有必要对此做深入的研究.本文针对悬浮物较少的水域,选用7个滇池水样,采用不同滤膜、不同预处理方法、不同消解用酸及消解时间,测定并比较砷空白值,试图通过改变实验条件降低空白值,探索前处理的最佳条件及步骤.结果表明,对于悬浮物较少的湖泊水域,采用预称重的醋酸纤维膜过滤水样、载有颗粒物的滤膜冷冻干燥、HNO3-HCl O4加热共消解36 h,消解上清液用氢化物发生原子荧光光度计测定砷空白值低于悬浮物一个数量级以上,膜空白砷相对标准偏差为2.80%~11.38%,膜空白加标回收率为83%~103%;与滇池5个实际样品验证误差范围0.27%~6.92%.此方法可以可靠地获得悬浮物中的砷含量,在砷含量较低的水体悬浮物测定方面具有优势.

Determination of trace arsenic on suspended solids of lake water

The study of the partition of heavy metals in suspended solids and water phase is important. It is highly significant to understand the sources, migration and transformation as well as ecological and healthy effects of heavy metal in aquatic system. Arsenic in water has caused serious damages to human health which has raised concerns over last decades. However, previous studies on the sample pretreatment and determination method of trace arsenic in the suspended solids, as well as quality control, remain largely uncertain. In this study, 7 water samples collected in Lake Dianchi were tested in a series of experiments, by using different filters, digestion/extraction acids/duration and methods of digestion/extraction. Blank filter membranes were determined to ultimately reduce the effect of filters on arsenic determination in suspended solids. In this way, we developed an optimized method in the determination of trace arsenic in the suspended solids of lakes. Briefly, the method includes the following steps. First, the pre-weighed cellulose acetate membranes are used to filter a 100 mL water at the sampling site in situ; Then, the membranes with suspended solids are freeze dried, re-weighed, and digested in nitric acid and perchloric acid on an electric hot plate; At last, the supernatant of the digestion is determined for arsenic by using a hydrogen generation atomic fluorescence spectrometer. The results show that arsenic blanks in the filter membranes were less than one order of magnitude of the arsenic contents in the suspended solids, and the RSD for membrane blank repetitions were in range of 2.80%~11.38%, while arsenic spiked recoveries were within 83%~103%. Validation of the method shows that the range of difference as 0.27%~6.92% between the data via this method and a field survey of 5 samples from Lake Dianchi. This method is reliable and has advantages in the determination of trace arsenic in suspended solids.