电动胶束色谱中弱酸性化合物的柱上浓缩富集技术的研究

On- Column Sample Stacking of Weakly Acidic Compounds in Micellar Electrokinetic Chromatography

提出一种电动胶束色谱（ＭＥＫＣ）中弱酸性化合物的柱上浓缩富集技术，并得到实验证实。以七种弱酸性巴比妥类药物的ＭＥＫＣ分离为例，考察了样品溶剂中表面活性剂浓度、ｐＨ值和离子强度等对富集作用的影响。表面活性剂浓度，ｐＨ值对富集效应的影响较大。采用低浓度（略高于ＣＭＣ点）表面活性剂、低浓度缓冲液作样品溶剂，调节溶剂ｐＨ值小于待测化合物的ｐＫａ－１，就可以对弱酸性化合物进行柱上富集。采用这种富集技术，可以压缩样品带的宽度从而提高柱效，在此基础上可通过加大进样量提高化合物的检测灵敏度。这种方法不仅适用于弱酸性有机化合物，也可用于弱碱性有机化合物的柱上浓缩富集。

n-column sample stacking is an effective way to increase injection volurne in high performance capillaryclcctrophoresi:separation,and thus is an easy approach to enhance detection sensitivity.It has been extensivcly studied in capillary zone electrophoresis.In micellar electrokinetic chromatography,as we know,onereport by Y.Z. LIU and his colleague in 1994 has described on- column sample stacking for neutralmolectiles.In this paper,we proposed a simple and easy method to stack on-column samples of weakly acidiccornpounds In miccller electrokinetic chromatography. For stacking of weakly acidic compounds,the principleof the method is that pH valuc of 10mmol/L sodium dodecyl sulfate solution used as sample solvent is adjust-cd to less than pKa- 1(here pKa is the lowest one of te:tacidic compounds)by the addition of low concen-trdrtion of buffcr. so.that acidic compounds exist mainly in species of neutral molecules and is resolved in mi-celles. and that as soon as running voltage is applied,micelles carry sample molecules to the boundary be-twL2Cn sample zone and run buffer,and samples are stacked tbere,For the stacking of basic(or cationic)compounds,pH value of:ample solvent(low concentratioii of micelles and low concentration of buffer)is ad-justed to hlgher than pKw- pKb+1(where pKw is thermodynamic constant for water,and pKb is the great-ext one of the tested compounds),so that the compounds exist mainly in molecular species and can bestacked.On- column stacking is simply performed by dissolving samples in 10mmol/L of sodium dodecyl sul-fatc plus 5mmol/L or less of buffer at the required pH value,The proposed stacking technique is demonstrated and proved by micellar electrokinetic chromatography separation of 7 barbiturates.