阳离子交换色谱中色谱柱温度对碱金属与碱土金属离子保留的影响

研究了非抑制型阳离子交换色谱中色谱柱温度(25~50℃)对碱金属离子(Li+、Na+、K+、Rb+)和碱土金属离子(Mg2+、Ca2+、Sr2+)以及NH4+保留的影响。在Shim-pack IC-C1磺酸型阳离子交换柱上,以硝酸为流动相分离碱金属离子,以乙二胺或乙二胺-草酸(柠檬酸)为流动相分离碱土金属离子,随着色谱柱温度的升高,碱金属和碱土金属离子的保留时间均增长,其范特霍夫曲线具有良好的线性关系,斜率为负值,表明在此条件下碱金属和碱土金属离子的保留为吸热过程。在Shim-pack IC-SC1羧酸型阳离子交换柱上,以硫酸为流动相同时分离碱金属和碱土金属离子,随着色谱柱温度的升高,Mg2+、Ca2+的保留时间增长,而K+、Rb+的保留时间缩短,Li+、Na+、NH4+的保留时间基本不变。在此条件下,Mg2+、Ca2+、K+和Rb+的范特霍夫曲线具有良好的线性关系,其中Mg2+和Ca2+的曲线斜率为负值,K+和Rb+的曲线斜率为正值,表明Mg2+和Ca2+的保留表现为吸热过程,K+和Rb+的保留表现为放热过程。研究表明在不同固定相和流动相条件下,色谱柱温度对碱金属和碱土金属离子保留行为的影响不同。

Effect of Column Temperature on the Retention of Alkali Metal and Alkaline Earth Metal Ions in Cation-exchange Ion Chromatography

The effects of column temperatures varying from 25 ℃ to 50 ℃ on the retention times of alkali metal ions(Li~+,Na~+,K~+,Rb~+),alkaline earth metal ions(Mg~(2+),Ca~(2+),Sr~(2+)) and ammonium ion(NH+4) were studied by non-suppressed cation-exchange ion chromatography.When nitric acid was used as mobile phase for separating alkali metal ions and ethylenediamine or ethylenediamine-oxalic acid as mobile phase for separating alkaline earth metals ions on Shim-pack IC-C1 of sulfonic cation-exchange column,the retention times of alkali metals and alkaline earth metal ions increased with the increase of column temperatures.The Van't Hoff plots for those ions were all linear with negative slopes indicating that the retention was of an endothermic process.When alkali metal and alkaline earth metal ions were simultaneously separated using sulfuric acid as mobile phase on Shim-pack IC-SC1 of carboxylic acid cation-exchange column,the retention times of Mg~(2+) and Ca~(2+) increased and K~+ and Rb~+ decreased with the increase of column temperatures,but those of Li~+,Na~+ and NH+4 ions varied insignificantly.The Van't Hoff plots for Mg~(2+) and Ca~(2+) were linear with negative slopes and those for K~+ and Rb~+ were linear with positive slopes indicating that the retention for Mg~(2+) and Ca~(2+) was of an endothermic process and that for K~+ and Rb~+was an exothermic one.The results showed that the effects of column temperatures on the retentions of alkali metal and alkaline earth metal ions varied with different stationary phases and mobile phases.