Zhang C X, Thormann W
Department of Clinical Pharmacology, University of Bern, Switzerland.
Anal Chem. 1998 Feb 1;70(3):540-8. doi: 10.1021/ac9707085.
In capillary electrophoresis, head-column field-amplified sample stacking (FASS) provides the largest sensitivity enhancement of all electrokinetic concentration techniques (Zhang, C.-X.; Thormann, W. Anal. Chem. 1996, 68, 2523). Application of head-column FASS to the analysis of closely related opioids by capillary zone electrophoresis in binary systems with ethylene glycol is described. It is shown that sample condensation is further increased about 2-fold by introduction of a preinjection plug, i.e., introduction of a short solution plug of high conductivity, high pH, and high viscosity at the capillary tip prior to injection. The preinjection plug acts as a temporary trap for solutes. Its effective length is shown to be limited to a few millimeters. The highest sample stacking efficiency in head-column FASS is obtained via optimization of the electric field strength and the effective electrophoretic mobility of the solutes within the sample and the adjacent zones and is thus strongly dependent on the compositions of both the sample matrix and the preinjection plug. Binary sample solutions of low conductivity and low viscosity containing small amounts of a weak acid are demonstrated to be most effective for the stacking of positively charged opioids. The procedure developed for capillary zone electrophoresis of opioids in binary systems with ethylene glycol and UV absorbance detection is documented to provide a 3 orders of magnitude sensitivity enhancement, exhaustive sample injection from an external reservoir of up to 20 microL (i.e., from a volume that is more than 20-fold the volume of the capillary employed), and a lowest detectable concentration of 0.1 ng/mL (S/N = 3). Using internal calibration, typical intraday and interday imprecisions of solute concentrations between 3 and 10 ng/mL and between 0.5 and 1.5 ng/mL are < or = 5% and < or = 15%, respectively. The stacking approach has been successfully applied to the analysis of dihydrocodeine in extracts of 20 microL of human plasma and is shown to permit the precise (imprecision < or = 10%) determination of dihydrocodeine plasma levels of pharmacological interest (3-300 ng/mL or 10-1000 nM). Furthermore, using a modified protocol for micellar electrokinetic chromatography, head-column FASS is shown to provide a 400-fold sensitivity enhancement for a number of opioids. The stacking procedure is based on insertion of a surfactant-free preinjection plug and temporary application of reversed voltage after electroinjection.
在毛细管电泳中，柱头场放大进样堆积（FASS）是所有电动富集技术中灵敏度提高幅度最大的方法（张，C.-X.；托曼，W.《分析化学》，1996年，68卷，2523页）。本文描述了将柱头FASS应用于在含有乙二醇的二元体系中通过毛细管区带电泳分析密切相关的阿片类药物。结果表明，通过引入预进样塞，即进样前在毛细管尖端引入一个高电导率、高pH值和高粘度的短溶液塞，样品浓缩进一步提高了约2倍。预进样塞起到溶质的临时陷阱作用。其有效长度被证明限制在几毫米。柱头FASS中最高的样品堆积效率是通过优化电场强度以及样品和相邻区域中溶质的有效电泳迁移率获得的，因此强烈依赖于样品基质和预进样塞的组成。含有少量弱酸的低电导率和低粘度二元样品溶液被证明对带正电的阿片类药物的堆积最为有效。所开发的用于在含有乙二醇的二元体系中对阿片类药物进行毛细管区带电泳和紫外吸收检测的方法被证明可使灵敏度提高3个数量级，可从高达20微升的外部储液器中进行完全进样（即进样体积比所用毛细管体积大20多倍），最低检测浓度为0.1纳克/毫升（信噪比=3）。使用内标法，溶质浓度在3至10纳克/毫升和0.5至1.5纳克/毫升之间时，典型的日内和日间不精密度分别≤5%和≤15%。该堆积方法已成功应用于20微升人血浆提取物中双氢可待因的分析，并被证明能够精确（不精密度≤10%）测定具有药理学意义的双氢可待因血浆水平（3至300纳克/毫升或10至1000纳摩尔）。此外，使用一种改进的胶束电动色谱方法，柱头FASS被证明可使多种阿片类药物的灵敏度提高400倍。该堆积方法基于插入无表面活性剂的预进样塞并在电进样后临时施加反向电压。
