离子交换与离子排斥色谱柱串联体系中阳离子的多峰现象及其机理

研究了串联柱体系中阳离子的“多峰现象”。在阳离子交换柱后面接上阴离子分析用的离子排斥柱构成一个串联柱体系，当以酒石酸（ＴＡ）和吡啶二羧酸（ＰＤＣ）的混合溶液作淋洗液时，每一种阳离子同时出现３个色谱峰。这是因为从阳离子交换柱流出的阳离子与有络合作用的两种淋洗剂阴离子形成络合物，使流动相中淋洗剂阴离子浓度减少以及两种淋洗剂阴离子在离子排斥柱中被保留且保留值不同。

Elution Behaviors of Cations on the Serial Columns Combining a Cation Exchange Column with an Ion Exclusion Column

The elution behaviors of cations (Na+, NH4+, K+, Ca2+ and Mg2+) on the serially connected cation exchange column (ICS-C25) and ion exclusion column (TSKgel OApak-A) were investigated. As shown in Figure 1, three peaks were observed for each cation when a mixture of tartaric acid (TA) and 2,6-pyridinedicarboxylic acid (PDC) was used as eluent. In ion exchange chromatography, the background conductivity (G0) of carboxylic acid (HR) eluent which is based on the dissociation of HR, can be expressed as follows: G0 = C0H lambdaH + C0R lambdaR (1) where C0H and C0R are the initial concentration, lambdaH and lambdaR are the equivalent concentration of H+ and R-, respectively. The concentration of eluent anion R- in mobile phase is reduced when the cations (M) are eluted from cation exchange column, because the R- forms some complexes with the cations. At this time, the conductivity (G) of the eluent will be G = CM lambdaM + (C0R - C'R) lambdaR + (C0H - CM) lambdaH (2) where CM is the concentration of cations, and C'R is a reduce of R-. The peaks on chromatogram results from a change in conductance (deltaG), and in the conditions of the paper. DeltaG = G - G0 = CM (lambdaM - lambdaH) - C'TA lambdaTA - C'PDC lambdaPDC (3). On the ion exclusion column, the eluent anion TA and PDC were retained at different capacity factor by an ion exclusion mechanism while the cations have not any retention. That is to say, the first peak of each cation is caused by elution of the cation and the depletion of eluent ion (H+) in the mobile phase. The second and third peaks have appeared corresponding to the depletion of TA and PDC anion in mobile phase, respectively.