Skip to main content
SpringerLink
Log in

Investigation of internal pressure gradients generated in electrokinetic flows with axial conductivity gradients

  • Research Article
  • Published:
Experiments in Fluids Aims and scope Submit manuscript

Abstract

Field amplified sample stacking (FASS) is used to increase sample concentrations in electrokinetic flows. The technique uses conductivity gradients to establish a non-uniform electric field that accumulates ions within a conductivity gradient, and can be readily integrated with capillary electrophoresis. Conductivity gradients also cause gradients in near-wall electroosmotic flow velocities. These velocity gradients generate internal pressure gradients that drive secondary, dispersive flows. This dispersion leads to a significant reduction in the efficiency of sample stacking. This paper presents an experimental investigation of internally generated pressure gradients in FASS using micron-resolution particle image velocimetry (μPIV). We measure velocity fields of particles seeded into an electrokinetic FASS flow field in a glass microchannel with a single buffer–buffer interface. μPIV allows for the direct quantification of local, instantaneous pressure gradients by analyzing the curvature of velocity profiles. Measurements show internally generated pressure-driven velocities on the order of 1mm/s for a typical applied electric field of 100 V/cm and a conductivity ratio of 10. A one-dimensional (1D) analytical model for the temporal development of the internal pressure gradient generation is proposed which is useful in estimating general trends in flow dynamics.

This is a preview of subscription content, log in via an institution to check access.

Access this article

Log in via an institution

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Institutional subscriptions

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5

Similar content being viewed by others

Notes

  1. An ideal flow tracer would have zero electrophoretic mobility, but stability of the seed particle colloidal dispersion depends largely on surface charge. Aqueous solutions of uncharged particles, if realizable, are expected to suffer from particle flocculation, adsorption to the walls, and perhaps precipitation.

Abbreviations

E :

applied electric field

U :

liquid velocity

L :

length of the channel

α:

length of the high conductivity segment (xD) non-dimensionalized by L

σ:

electrolyte conductivity

ν :

electroosmotic wall mobility

γ:

ratio of electrolyte conductivities

eof:

electroosmotic flow

p:

pressure-driven flow

eph:

electrophoretic

BGE:

back ground electrolyte

s:

sample zone

References

  • Anderson JL, Idol WK (1985) Electroosmosis through pores with nonuniformly charged walls. Chem Eng Commun 38:93–106

    Article  Google Scholar 

  • Bharadwaj R, Santiago JG (2005) Dynamics of field-amplified sample stacking. J Fluid Mech 543:57–92

    Article  MATH  Google Scholar 

  • Burgi DS, Chien RL (1991) Optimization in sample stacking for high-performance capillary electrophoresis. Anal Chem 63(18):2042–2047

    Article  Google Scholar 

  • Chen CH et al (2005) Convective and absolute electrokinetic instability with conductivity gradients. J Fluid Mech 524:263–303

    Article  MATH  Google Scholar 

  • Chien RL, Burgi DS (1991) Field amplified sample injection in high-performance capillary electrophoresis. J Chromatogr 559(1–2):141–152

    Article  Google Scholar 

  • Chien R, Burgi D (1992) Sample stacking of an extremely large injection volume in high-performance capillary electrophoresis. Anal Chem 64(9):1046–1050

    Article  Google Scholar 

  • Coleman HW, Steele GW (1989) Experimentation and uncertainty analysis for engineers, 1st edn. Wiley, New York

  • Devasenathipathy S, Santiago J, Takehara K (2002) Particle tracking techniques for electrokinetic microchannel flows. Anal Chem 74(15):3704–3713

    Article  Google Scholar 

  • Huang XH, Gordon MJ, Zare RN (1988) Current-monitoring method for measuring the electroosmotic flow-rate in capillary zone electrophoresis. Anal Chem 60(17):1837–1838

    Article  Google Scholar 

  • Hunter RJ (1981) Zeta potential in colloid science. Academic, London

    Google Scholar 

  • Jacobson SC, Ramsey JM (1995) Microchip electrophoresis with sample stacking. Electrophoresis 16(4):481–486

    Article  Google Scholar 

  • Jacobson SC, Hergenroder R, Koutny LB, Ramsey JM (1994) High-speed separations on a microchip. Anal Chem 66(7):1114–1118

    Article  Google Scholar 

  • Kasicka V et al (1997) Capillary zone electrophoresis with external radial electric field control of electroosmotic flow and its application to the separation of synthetic oligopeptides. J Chromatogr A 772(1–2):221–230

    Article  Google Scholar 

  • Kim MJ, Beskok A, Kihm KD (2002) Electro-osmosis-driven micro-channel flows: a comparative study of microscopic particle image velocimetry measurements and numerical simulations. Exp Fluids 33(1):170–180

    Google Scholar 

  • Lin H et al (2004) Instability of electrokinetic microchannel flows with conductivity gradients. Phys Fluids 16(6):1922–1935

    Article  Google Scholar 

  • Manz A, Harrison DJ, Verpoorte EMJ, Fettinger JC, Paulus A, Ludi H, Widmer HM (1992) Planar chips technology for minituarization and integration of separation techniques into monitoring systems: capillary electrophoresis on a chip. J Chromatogr 593:253–258

    Article  Google Scholar 

  • Meinhart CD, Wereley ST, Gray MHB (2000) Volume illumination for two-dimensional particle image velocimetry. Measure Sci Technol 11(6):809–814

    Article  Google Scholar 

  • Olsen MG, Adrian RJ (2000) Out-of-focus effects on particle image visibility and correlation in microscopic particle image velocimetry. Exp Fluids 29:S166–S174

    Article  Google Scholar 

  • Quirino J, Terabe S (1999) Sample stacking of fast-moving anions in capillary zone electrophoresis with pH-suppressed electroosmotic flow. J Chromatogr A 850(1–2):339–344

    Article  Google Scholar 

  • Raviv U, Laurat P, Klein J (2002) Time dependence of forces between mica surfaces in water and its relation to the release of surface ions. J Chem Phys 116(12):5167–5172

    Article  Google Scholar 

  • Ren CL, Li DQ (2006) Electrokinetic sample transport in a microchannel with spatial electrical conductivity gradients. J Colloid Interface Sci 294(2):482–491

    Article  Google Scholar 

  • Ross D, Gaitan M, Locascio LE (2001) Temperature measurement in microfluidic systems using a temperature-dependent fluorescent dye. Anal Chem 73(17):4117–4123

    Article  Google Scholar 

  • Sadr R et al (2004) An experimental study of electro-osmotic flow in rectangular microchannels. J Fluid Mech 506:357–367

    Article  MATH  Google Scholar 

  • Santiago JG (2001) Electroosmotic flows in microchannels with finite inertial and pressure forces. Anal Chem 73(10):2353–2365

    Article  Google Scholar 

  • Szymczyk A et al (1999) An application of the space charge model to the electrolyte conductivity inside a charged microporous membrane. J Memb Sci 161(1–2):275–285

    Article  Google Scholar 

  • Thormann W et al (1998) Modeling of the impact of ionic strength on the electroosmotic flow in capillary electrophoresis with uniform and discontinuous buffer systems. Anal Chem 70(3):549–562

    Article  Google Scholar 

  • Wainright A et al (2002) Sample pre-concentration by isotachophoresis in microfluidic devices. J Chromatogr A 979(1–2):69–80

    Article  Google Scholar 

  • White FM (1991) Viscous fluid flow, 2nd ed. McGraw-Hill Series. In: Holman JP, Lloyd JR (eds) Mechanical engineering. McGraw-Hill, New York, pp 614

  • Yang H, Chien RL (2001) Sample stacking in laboratory-on-a-chip devices. J Chromatogr A 924(1–2):155–163

    Article  Google Scholar 

Download references

Author information

Author notes

  1. Shankar Devasenathipathy

    Present address: Intel Corporation, Assembly & Test Technology Development, 5000 W Chandler Blvd, Chandler, AZ, 85226, USA

  2. Rajiv Bharadwaj

    Present address: Caliper Life Sciences, 605 Fairchild Drive, Mountain View, CA, 94043, USA

Authors and Affiliations

  1. Mechanical Engineering Department, Stanford University, 440 Escondido Mall, Stanford, CA, 94305, USA

    Shankar Devasenathipathy, Rajiv Bharadwaj & Juan G. Santiago

Authors
  1. Shankar Devasenathipathy
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Rajiv Bharadwaj
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Juan G. Santiago
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Juan G. Santiago.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Devasenathipathy, S., Bharadwaj, R. & Santiago, J.G. Investigation of internal pressure gradients generated in electrokinetic flows with axial conductivity gradients. Exp Fluids 43, 959–967 (2007). https://doi.org/10.1007/s00348-007-0366-3

Download citation

  • Received:

  • Revised:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1007/s00348-007-0366-3

Keywords

Search

Navigation