Column Design for Electrochemically Modulated Liquid Chromatography

Ting, En Yi; Porter, Marc D.

doi:10.1021/ac970815z

Cited by 31 publications

(45 citation statements)

References 19 publications

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“…Such a dependence reflects how E app affects the electrostatic interactions between an ionic species and a charged stationary phase via the ion distribution law. 8,30 Second, the slope of such a plot represents the sensitivity of retention to changes in E app . The plots show that the divalent anion 1,5-NDS is roughly twice as sensitive to changes in E app when compared to the three monovalent anions: BS, MBS, and CBS.…”

Section: Effects Of E Appmentioning

confidence: 99%

High-Speed Electrochemically Modulated Liquid Chromatography

Ponton

Porter

2004

Anal. Chem.

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The performance advantages of carrying out electrochemically modulated liquid chromatography (EMLC) at elevated temperatures and mobile-phase flow rates are investigated. EMLC has the unique ability to manipulate analyte retention and enhance separation efficiencies through changes in the potential applied to a conductive stationary phase. Operation of high-performance liquid chromatography systems at elevated column temperatures also provides pathways to improve chromatographic performance by enhancing analyte diffusivity and facilitating the use of higher mobile-phase flow rates than conventionally attainable. The results show that performing EMLC separations at elevated temperatures (e.g., 100 °C) reduces the analysis time of a mixture of aromatic sulfonates in a mixed mobile phase by more than a factor of 20. Moreover, use of higher operating temperatures enables the separation of this mixture with an entirely aqueous mobile phase in less than 2 min. This paper investigates the advantages of performing separations using electrochemically modulated liquid chromatography (EMLC) at elevated column temperatures. EMLC is a unique chromatographic technique that manipulates retention through changes in the potential applied (E app ) to a conductive stationary-phase-like porous graphitic carbon (PGC). This capability is realized by fashioning a high-performance liquid chromatography (HPLC) column into an electrochemical cell and utilizing the packing as both a chromatographic stationary phase and as a working electrode. As a consequence, a change in E app alters the effective surface composition of the stationary phase and, in turn, retention. 1 Several laboratories, 2-5 including our own, 6-10 have demonstrated that EMLC can be utilized for the separation of a wide range of mixtures (e.g., aromatic sulfonates, 10 monosubstituted benzenes, 9 protonated pyridines and anilines, 11 corticosteroids, 7 benzodiazepines, 6 short-chain alkanoic acids, 12 and metal ion complexes 13 ).Recent studies have shown that elevated column temperatures can also be used to manipulate retention in HPLC by significantly reducing analysis times while maintaining an effective separation. 14-16 This observation was theoretically predicted several years ago 17,18 and comes about because of three different temperature-dependent phenomena. First, retention in most reversed-phase separations is an exothermic process. 19-21 An increase in column temperature therefore leads to a decrease in elution time. Second, the viscosity of most mobile phases decreases with increasing temperature. As a consequence, the back pressure of the HPLC system decreases, enabling operation at higher flow rates. Third, higher column temperatures increase analyte diffusivity and desorption kinetics. Enhanced diffusivity increases the efficiency of a separation by lowering the C-term in the van Deemter equation, 22 which counters the loss in efficiency that arises at higher mobile-phase flow rates.

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Section: Effects Of E Appmentioning

confidence: 99%

High-Speed Electrochemically Modulated Liquid Chromatography

Ponton

Porter

2004

Anal. Chem.

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“…We note that, using the differences in absorption spectra in the ultraviolet between the neutral and ionized species and the method described by Albert and Serjeant [27], the value of pKai was found to be 9.4 and that of pKa2 to be 12.8. Both are in good agreement with literature data determined potentiometrically [25]. shifted to 294 nm.…”

Section: Methodssupporting

confidence: 92%

“…The extinction coefficient for this feature at 294 nm is 3825 M"'cm"'. We assign this band as a k-^k absorption in the catechol ligand [25,28]. Two well-defined isosbestic points indicate that only one form of the complex is present under the experimental conditions employed.…”

Section: Methodsmentioning

confidence: 89%

“…its metal complex, the ability of CAT to bind Co(II) was studied. Co(II) was selected because of its relatively high stability constant for the formation of complexes with CAT, its negligible absorbance in the UV region, and its simple complexation chemistry with CAT in comparison to the other metal ions [25,26].…”

Section: Methodsmentioning

confidence: 99%

“…In order to overcome this issue, a new column design was developed [25,26] This revolution in the column design resulted in a major improvement in chromatographic performance, and therefore opened the door for the application of this technique to a wide area. Efforts in our group [25][26][27][28] have demonstrated that this approach can be applied to manipulate the separations of a variety of different analytes, including aromatic sulfonates, corticosteroids, and benzodiazepines. It was also applied for enantiomeric separations [29].…”

Section: Emlc Is Another Alternative Technique and Combines Electrochmentioning

confidence: 99%

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Electrosorption

Hatton

2016

Kirk-Othmer Encyclopedia of Chemical Technology

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The topic of electrosorption is introduced, especially as it applies to electroseparations. Through the application of electrochemical potential, the interaction of target compounds with an electrode interface can be modulated, thus resulting in efficient and environmentally friendly applications.The major classes of separations utilizing electrosorption are discussed, and an overview of the most common materials chemistry is given. Capacitive deionization is an upcoming method for removing salt by using porous electrodes and the double layer, and in parallel, redox‐mediated separations based on Faradaic processes have been gaining intense attention for specialized separation processes.The various mechanisms for electrosorption as well as application fields are discussed, including water treatment, water purification, and chromatographic separations.

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Column Design for Electrochemically Modulated Liquid Chromatography

Cited by 31 publications

References 19 publications

High-Speed Electrochemically Modulated Liquid Chromatography

High-Speed Electrochemically Modulated Liquid Chromatography

Issues related to the development and application of electrochemically modulated liquid chromatography (EMLC)

Electrosorption

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