Analytical Separations Using Molecular Micelles in Open-Tubular Capillary Electrochromatography

Abstract

Open-tubular capillary electrochromatography (OT-CEC) is an alternative approach to conventional CEC. The primary advantage of OT-CEC is the elimination of problems associated with frits and silica particles in conventional CEC. This report is an investigation of the utility of using a polymeric surfactant (molecular micelle) for OT-CEC. In this approach, fused-silica capillaries coated with thin films of physically adsorbed charged polymers are developed by use of a polyelectrolyte multilayer (PEM) coating procedure. The PEM coating is constructed in situ by alternating rinses with positively and negatively charged polymers, where the negatively charged polymer is a molecular micelle. This can offer a number of advantages for separation of hydrophobic analytes. In this study, poly(diallyldimethylammonium chloride) was used as the cationic polymer and poly(sodium N-undecanoyl-L-glycinate) was used as the anionic polymer for PEM coating. The performance of the modified capillaries as a separation medium is evaluated by use of seven benzodiazepines as analytes. The run-to-run, day-to-day, week-to-week, and capillary-to-capillary reproducibilities of electroosmotic flow are very good with relative standard deviation values of less than 1% in all cases. In addition, the chromatographic performance of the monomeric form of the molecular micelle is compared for the separation of these analytes. The PEM-coated capillary was remarkably robust with more than 200 runs accomplished in this study. Strong stability against extreme pH values was also observed. The general utility of this approach is discussed in detail.

Towards a microchip‐based chromatographic platform. Part 2: Sol‐gel phases modified with polyelectrolyte multilayers for capillary electrochromatography

“…In contrast, the PEM coating shows no significant change in EOF or anion mobility for 100 consecutive separations, clearly indicating the increased stability of the chromatographic phase. While a full study of the stability of PEM coatings was beyond the scope of this work, we believe it will show similar stability to that previously reported [28,29].…”

“…The primary factor is the excellent stability of these coatings, as reported by Katayama et al [27] and Kapnissi et al [29], with the number of PEM layers employed significantly influencing the properties of the overall coating. Second, layer thickness is independent of the time of deposition and can be accurately controlled by changing the properties of the deposition solution.…”

“…This suggests considerable penetration of small analyte ions through the PEM for chromatographic interaction with the buried ion-exchange sites. This is further supported by a decrease in mobility of I 2 even with the anionic DS surface exposed, with the mobility decreasing from 264610 29 PEM coating and its relation to the size of the sol-gel mesopores. Given our deposition of polyelectrolytes from a very low ionic strength solution, it is anticipated that the layer thickness will only be marginally thicker than layers deposited from water.…”

“…In addition to enhanced stability, Graul and Schlenoff [26] demonstrated the potential of this approach for chromatography by separating a mixture of neutral solutes in open-tubular CEC with a functionalized PEM-coating chromatographic phase. Kapnissi et al [29] used this technique for separations of benzodiazepines using PEM open-tubular CEC. Again, the stability and reproducibility of these columns was exceptional, with 200 separations performed on a single column after exposure to extreme acidic and basic conditions.…”

Method Development by Use of Capillary Electrophoresis and Applications in Pharmaceutical, Biological and Natural Samples

“…This usually provides higher efficiencies and rapid analysis. They have, over the years, been extensively used in a BGE [74][75][76][77][78][79][80], in a polyelectrolyte multilayer coating [63,74,[81][82][83], and in a CE-MS system [84][85][86].…”