Electroosmotic Flow Phenomena in Packed Capillaries:  From the Interstitial Velocities to Intraparticle and Boundary Layer Mass Transfer

Tallarek, Ulrich; Rapp, Erdmann; Seidel‐Morgenstern, A.; As, Henk Van

doi:10.1021/jp020605c

Cited by 31 publications

(30 citation statements)

References 95 publications

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“…Axial plate heights and dispersion coefficients reduced by more than a dec-ade with respect to those typically found in capillary HPLC have been reported for capillary electrochromatography (CEC) [70][71][72]. This massive improvement is mainly caused by a strong electrokinetic flow field perfusion in the beds of porous particles, which operates with substantial intraparticle EOF velocities even under conditions favoring strong EDL overlap on intraparticle pore level [69,73,74]. The effect of intraparticle EOF on mass transfer of electroneutral analyte has been visualized and analyzed recently with quantitative confocal laser scanning microscopy studies [75,76].…”

Section: Introductionmentioning

confidence: 97%

“…Concerning fluid flow through random sphere packings in capillary columns with a relatively low hydraulic permeability EOF has demonstrated superior conductivity and dispersion behavior as compared to pressure-driven flow, accompanying a reduction of velocity extremes in the mobile-phase flow pattern [61][62][63][64][65][66][67][68][69]. Axial plate heights and dispersion coefficients reduced by more than a dec-ade with respect to those typically found in capillary HPLC have been reported for capillary electrochromatography (CEC) [70][71][72].…”

Section: Introductionmentioning

confidence: 99%

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Nonlinear electroosmosis in hierarchical monolithic structures

Nischang

Tallarek

2004

Electrophoresis

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We studied the dependence of electroosmotic flow (EOF) velocity and separation efficiency for neutral analytes in 100 microm ID capillary monoliths on a variation of the mobile phase ionic strength and applied electrical field strength, i.e., we covered a range for the concentration of Tris buffer from 10(-5) to 10(-2) M and applied electrical field strengths up to 10(5) V/m. The silica-based monoliths are hierarchically structured having intraskeleton mesopores and interskeleton macropores. While a linear dependence of the average EOF velocity on applied field strength could be observed with 5 x 10(-3) M Tris (turning slightly nonlinear at a higher concentration due to thermal effects), this dependence becomes systematically nonlinear as the Tris concentration is reduced towards 10(-4) M. Increased velocities by more than 50% compared to those expected from linear behavior are realized at 10(5) V/m. Concomitantly, as the Tris concentration is reduced from 10(-3) to 10(-4) M, we notice an improvement in plate heights by a factor of more than 2 (they approach 2 microm for ethylbenzoate). We complementary analyzed the onset of the nonlinear EOF dynamics in a hierarchical monolith and the significantly reduced axial dispersion in view of nonequilibrium electrokinetic effects which may develop in porous media due to the presence of ion-permselective regions, e.g., the mesoporous monolith skeleton. In this respect, a decreasing mobile phase ionic strength favors the formation of nonequilibrium concentration polarization in strong electrical fields, and a coupling of the electrostatics and hydrodynamics then may explain nonlinear EOF velocities and increasing separation efficiencies depending on the Tris concentration and applied field strength.

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Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Nonlinear electroosmosis in hierarchical monolithic structures

Nischang

Tallarek

2004

Electrophoresis

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“…CEC, which is often described as a hybrid of CZE and LC [6,7], has demonstrated higher separation efficiencies and flow permeabilities than capillary HPLC [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. The use of silica-based stationary phases with reversed-phase properties in CEC is well established at medium and higher mobile phase pH, where dissociated residual silanol groups provide the necessary surface charge for a suitable EOF.…”

Section: Introductionmentioning

confidence: 99%

Electrochromatographic retention of peptides on strong cation‐exchange stationary phases

Nischang¹,

Höltzel²,

Tallarek³

2010

Electrophoresis

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We analyze the systematic and substantial electrical field-dependence of electrochromatographic retention for four counterionic peptides ([Met5]enkephalin, oxytocin, [Arg8]vasopressin, and luteinizing hormone releasing hormone (LHRH) ) on a strong cation-exchange (SCX) stationary phase. Our experiments show that retention behavior in the studied system depends on the charge-selectivity of the stationary phase particles, the applied voltage, and the peptides' net charge. Retention factors of twice positively charged peptides ([Arg8]vasopressin and LHRH at pH 2.7) decrease with increasing applied voltage, whereas lower charged peptides (oxytocin and [Met5]enkephalin at pH 2.7, [Arg8]vasopressin and LHRH at pH 7.0) show a concomitant increase in their retention factors. The observed behavior is explained on the basis of electrical fieldinduced concentration polarization (CP) that develops around the SCX particles of the packing. The intraparticle concentration of charged species (buffer ions, peptides) increases with increasing applied voltage due to diffusive backflux from the enriched CP zone associated with each SCX particle. For twice charged and on the SCX phase strongly retained peptides the local increase in mobile phase ionic strength reduces the electrostatic interactions with the stationary phase, which explains the decrease of retention factors with increasing applied voltage and CP intensity. Lower charged and weaker retained peptides experience a much stronger relative intraparticle enrichment than the twice-charged peptides, which results in a net increase of retention factors with increasing applied voltage. The CP-related contribution to electrochromatographic retention of peptides on the SCX stationary phase is modulated by the applied voltage, the mobile phase ionic strength, and the peptides' net charge and could be used for selectivity tuning in difficult separations.

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“…Thus, due to the strikingly different possibilities for tuning experimentally electroosmotic and hydraulic permeabilities of the packed bed, an important performance advantage of CEC over capillary HPLC lies in the new dimension of the perfusion mechanism. It has been shown that electroosmotic perfusion through fixed beds of porous particles proceeds with a significantly higher intraparticle permeability [55,98,99] and that, compared with hydraulic flow, the EOF offers far superior dispersion characteristics [50± 53]. Gigapores are definitely not needed for electroosmotic perfusion, and the pore space morphology should rather be optimized in view of the surface-to-volume ratio while maintaining substantial intraparticle EOF at a modest ionic strength.…”

Section: Electroosmotic Perfusive Flowmentioning

confidence: 99%

Dynamics of Capillary Electrochromatography: Experimental Study of Flow and Transport in Particulate Beds

et al. 2004

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The chromatographic performance with respect to the flow behavior and dispersion in fixed beds of nonporous and macroporous particles (having mean intraparticle pore diameters of 41, 105, and 232 nm) has been studied in capillary HPLC and electrochromatography. The existence of substantial electroosmotic intraparticle pore flow (perfusive electroosmosis) in columns packed with the macroporous particles was found to reduce stagnant mobile mass transfer resistance and decrease the global flow inhomogeneity over the column cross-section, leading to a significant improvement in column efficiency compared to capillary HPLC. The effect of electroosmotic perfusion on axial dispersion was shown to be sensitive to the mobile phase ionic strength and mean intraparticle pore diameter, thus, on an electrical double layer interaction within the particles. Complementary and consistent results were observed for the average electroosmotic flow through packed capillaries. It was found to depend on particle porosity and distinct contributions to the electrical double layer behavior within and between particles. Based on these data an optimum chromatographic performance in view of speed and efficiency can be achieved by straightforward adjustment of the electrolyte concentration and characteristic intraparticle pore size.

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Electroosmotic Flow Phenomena in Packed Capillaries: From the Interstitial Velocities to Intraparticle and Boundary Layer Mass Transfer

Cited by 31 publications

References 95 publications

Nonlinear electroosmosis in hierarchical monolithic structures

Nonlinear electroosmosis in hierarchical monolithic structures

Electrochromatographic retention of peptides on strong cation‐exchange stationary phases

Dynamics of Capillary Electrochromatography: Experimental Study of Flow and Transport in Particulate Beds

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