Application of Automatic Potentiometric Titrator in Continuous Titration of Six Indices in Groundwater
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摘要: 地下水中六项指标（pH、总碱度、氯离子、钙离子、镁离子及硫酸根）的分析需要对每个指标单独进行取样检测，步骤繁琐且效率较低。同时总碱度、氯离子、钙离子、镁离子及硫酸根通常采用手动目视滴定，检测结果存在人为操作误差，精密度和准确度相对较差。本文建立了准确快速测定地下水中六项指标的分析方法，只需2次取样，采用自动电位滴定仪自动判定终点，加液器可精确控制标准溶液加入量至0.1 μL，并且通过调整检测顺序、溶液酸度和加入掩蔽剂的方法消除相互干扰。本方法的加标回收率为93.5%~120.0%，相对标准偏差（RSD，n=10）为0.18%~11.33%。电位滴定法得到的数据相比标准方法的平行性更好，尤其是当所测定水样较为浑浊或者有颜色时测定数据更稳定。Abstract:
BACKGROUND The analysis of six indices (pH, total alkalinity, chloride ion, calcium ion, magnesium ion and sulfate radical) in underground water needed to be sampled separately for each index. The steps were tedious with low efficiency. Furthermore, the total alkalinity, chlorine ion, calcium ion, magnesium ion and sulfate radical usually used manual visual titration, resulting in manual operation error, poor precision, and inaccuracy. OBJECTIVES To establish an accurate and rapid method for the analysis of six indices in underground water. METHODS The method established and described in this paper only needed two samples and the Automatic Potentiometric Titrator could determine the end point automatically. The Automatic Potentiometric Titrator could accurately control the addition of standard solution to 0.1 μL, and eliminate mutual interference by adjusting the detection order, acidity and the addition of a masking agent. RESULTS The recoveries of this method are 93.5%-120.0%, and the relative standard deviations (RSDs, n=10) are 0.18%-11.33%. CONCLUSIONS The results obtained by potentiometric titration had better parallelism and stability, especially when the measured water samples were more turbid or colored. -
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表 1 自动电位滴定仪测量各指标所需的最佳仪器条件
Table 1. Optimal conditions for each index measured by automatic potentiometric titrator
待测
指标滴定
模式转子转速
(r/s)最小加液量
(μL)信号漂移速率
(mV/min)最大突跃
点个数pH pH(测量) 6 - - - 氯离子 DET-U 6 10 50 1 总碱度 DET-pH 6 10 50 2 总硬度
(钙镁)DET-U 6 50 100 2 硫酸根 DET-U 6 10 50 1 
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表 2 地下水中六项指标的加标回收率(n=12)
Table 2. Spiked recovery of six indexes in groundwater (n=12)
检测
指标加标量
(mg/L)平均回收率
(%)钙离子 8.7 105.0 镁离子 2.901 120.0 总硬度 33.71 111.4 氯离子 80 100.7 硫酸根 50 93.5 总碱度 44.03 100.5
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表 3 精密度试验和方法检出限
Table 3. Analytical results of precision test and detection limits of the method
检测
指标电位滴定法
精密度(%)RSD(%) 加标后
浓度
(mg/L)检出限(mg/L) 日内 日间 电位滴
定法标准
方法电位滴
定法标准
方法钙离子 1.56 2.25 1.96 7.73 5.00 0.54 4.0 镁离子 11.64 12.12 11.33 14.90 1.00 0.47 3.0 总硬度 4.56 3.14 3.78 7.86 16.60 3.28 10 氯离子 0.15 0.22 0.18 8.15 1.90 0.70 1.0 总碱度 3.39 1.48 2.57 8.88 2.00 0.57 2.5 硫酸根 6.98 11.08 8.86 9.68 17.4 0.72 10.0
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表 4 自动电位滴定法与标准方法结果的比较
Table 4. Comparsion of analytical results obtained by automatic potentiometric titration and national standard method
实验
编号pH 氯离子(mg/L) 总碱度(mg/L) 硫酸根(mg/L) 钙离子(mg/L) 镁离子(mg/L) 电极法 电位法 容量法 电位法 容量法 电位法 容量法 电位法 容量法 电位法 容量法 电位法 1 7.75 7.78 31.84 33.10 1353 1362 74.40 79.61 126.0 127.3 71.99 67.67 2 8.15 8.16 926.9 912.4 1494 1483 1032 1083 195.4 207.1 240.3 237.9 3 8.21 8.30 222.9 215.3 892.6 855.1 269.2 277.2 93.13 100.6 65.35 67.31 4 8.15 8.20 45.99 42.64 870.8 909.8 74.40 77.38 49.30 54.23 43.19 41.03 5 8.83 8.86 450.0 452.1 1050 1023 477.0 500.9 140.6 147.6 177.2 189.6 6 8.34 8.36 578.5 570.0 995.6 1026 385.1 389.0 166.2 177.8 146.2 144.7 7 8.16 8.21 440.5 433.7 930.3 930.3 641.2 673.2 120.5 119.7 173.3 183.7 8 7.74 7.39 870.3 863.8 963.5 986.4 862.2 841.8 328.7 312.3 237.0 253.6 9 7.98 7.92 479.4 475.5 708.0 729.3 558.0 530.1 157.0 151.3 86.39 85.03 10 8.31 8.26 125.0 118.4 1044 1081 196.9 187.1 68.48 63.69 91.37 90.46 11 8.11 8.06 675.7 665.3 1180 1215 645.5 632.6 166.2 162.9 235.9 249.5 12 8.24 8.22 14.15 14.77 735.8 713.7 37.20 39.43 71.22 77.63 29.90 27.81
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