离子色谱法和毛细管电泳法测定土壤中氯离子、硫酸根及其差异性

摘要

分别采用离子色谱法(IC)、毛细管电泳法(CE)两种仪器方法对不同pH土壤中Cl–、SO42–含量进行测定，并对其结果进行差异性分析。结果显示：参照标准物质的参考值(滴定法)，IC与CE测定值的准确度、回收率均满足实验分析要求，但精密度差异较大，IC(RSD,3.61%)的稳定性优于CE (RSD,8.97%)。据差异性(F与t检验)分析，两种仪器方法测定酸性土壤中 Cl–、SO42–含量存在显著性差异，而碱性、中性土壤的测定结果保持一致。对比4个被测样品基本性质发现，酸性土壤的 pH 与离子强度均低于其他样品，从而影响了石英毛细管的电渗流，最终改变了 CE 分离过程，这可能是Cl–结果偏离的主要因素。同时，对于IC，酸性土壤较中性、碱性土壤更易由于离子交换效应产生次级保留(拖尾)。此外，采用碱性分离体系分离酸性样品易形成结晶，从而导致SO42–含量的偏离。可见，两种方法各有优缺点。但是，IC较经典，而CE是一种新兴的仪器方法。测定像土壤这样基体较复杂的样品(特别是酸性土壤)中阴离子的仪器条件还需要进行更多摸索与优化，以促进这两种方法在土壤领域的推广与应用。%Chloride and sulfate in different soil samples with various pH were determined with Ion Chromatography (IC) and Capillary Electrophoresis (CE), respectively. The results showed that these two methods both worked well as the measured values of chloride and sulfate were consistent with these obtained with the standard titration method, but the relative standard deviation in measurements of CE (8.97%) was greater than that of IC (3.61%). The statisticalF-test andt-test showed that there was no significant difference on the measurements between the two methods for alkaline and neutral soils, but the significant difference was observed for the acid soil of ASA-5a. The lower pH and ionic strength of ASA-5a affected the electroosmotic flow (EOF) of fused silica capillary and changed the separation process of anions in CE, thus caused bigger deviation of measured chloride than other methods, i.e. IC and titration method. Meanwhile, acid soil samples could bring secondary retention of ions in IC measurements compared with other soils. Moreover, alkali eluent caused the formation of crystallization in separation process of acid soil samples with IC, which led to a bigger deviation of measured Sulfate than other methods, i.e. CE and titration methods. Therefore, CE and IC methods have their own merits and demerits. CE is a new method for measurements of soil chloride and sulfate, and more studies should be conducted to improve experimental conditions in the future, especially for acid soils.