双电极法现场快速检测地下水和湖水中碳酸氢根和碳酸根

地下水和湖水中碳酸氢根( HCO-3)和碳酸根( CO2-3)含量是地球化学碳行为和碳循环的重要表征,但两种离子的浓度易受环境影响而改变,因此,地下水和湖水中HCO-3和CO2-3真实含量的测定一直是个难题。实验利用CO2的水解平衡,通过pH电极和二氧化碳电极联用,建立了HCO-3和CO2-3现场快速测定的新方法,解决了地下水和湖水中HCO-3和CO2-3真实含量的测定难题。研究结果表明,在pH=4.8±0.1的底液中, HCO-3和CO2-3的线性范围分别为0.027~570 mg/L和1.25×10-8~39.7 mg/L。共存的金属离子、强酸阴离子(K+、Na+、Mg2+、Cl-、SO2-4,100 mg/L)、弱酸阴离子和弱酸(HSO-3、NO-2、HOAc,50 mg/L)对测定干扰小于5%。实际水样加标实验回收率在95.2%~99.2%之间,相对标准偏差为2.6%~3.7%。与酸碱滴定法进行对比,本方法的准确性良好。但方法受温度影响,因此标准溶液与样品应在同一温度下测量。总体而言,双电极法灵敏、快速、经济且电极携带方便、操作简单、对环境要求不高,十分适合现场和室内一般自然水体的快速检测。本方法已成功应用于青海省地下水和青海湖湖水中HCO-3和CO2-3的现场测定。实验表明,海东地区地下水样品pH在6.4~7.4之间,HCO-3含量为234~4096 mg/L,CO2-3含量为0.16~1.89 mg/L；青海湖湖水样品pH≈8.7,HCO-3含量范围在1.36~1.86 g/L,CO2-3含量在32.3~43.9 mg/L,与文献结果吻合。

Fast Detection of Carbonate and Bicarbonate in Groundwater and Lake Water by Coupled Ion Selective Electrodes

The content of bicarbonate ( HCO-3 ) and carbonate ( CO2-3 ) ions in groundwater and lake water reflects a broad set of carbon cycling reactions associated with decomposition or synthesis of organic compounds with mineral dissolution or precipitation, which indicates the local geochemical environment. However, the content of HCO-3 and CO2-3 changes easily under the influence of pH, temperature, atmosphere pressure in the process of sampling, transportation and storage, so it has been a worldwide problem to determine the real content of HCO-3 and CO2-3 ions in groundwater and lake water. This article proposed a new way to solve the problem by fast field detection of HCO-3 and CO2-3 ions through the use of pH electrode combined with carbon dioxide electrode. Studies showed in the base solution of pH=4. 8 ± 0. 1, the detection range of HCO-3 ion was 0. 027-570 mg/L and that of CO2-3 was 1. 25 ×10-8-39. 7 mg/L. In the most case, the coexisting ions and weak acid ( K+, Na+, Mg2+, Cl-, SO2-4 <100 mg/L;HSO-3 , NO-2 , HOAc<50 mg/L) did not interfere with the analysis. The method was validated for real water samples and the recoveries were in the range of 95. 2%-99. 2% with the relative standard deviations (RSDs) of 2. 6%-3. 7%. Compared with the acid-base titration method, the accuracy of this method had proved to be good. However, the method could be affected by temperature, so the standard solution and samples should be measured at the same temperature. Above all, this method is suitable for fast field analysis for HCO-3 and CO2-3 ions in the nature water as it is sensitive, fast, economical, and the electrodes are easy to carry and operate. It has been successfully applied in the determination of HCO-3 and CO2-3 in groundwater and lake water in Qinghai Province. Experiment showed that the pH of the groundwater samples from Haidong district was 6 . 4-7 . 4 , with 234-4096 mg/L HCO-3 and 0. 16-1. 89 mg/L CO2-3 . The pH of the lake water samples was about 8. 7, with 1. 36-1. 86 g/L HCO-3 and 32. 3-43. 9 mg/L CO2-3 , which was consistent with the previous results.