The influence of surface treatments on the electroosmotic flow in micellar electrokinetic capillary chromatography

Wu, Quanji; Claessens, H.A.; Cramers, C.A.M.G.

doi:10.1007/bf02275906

Cited by 18 publications

(8 citation statements)

References 35 publications

(21 reference statements)

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“…In our experiments, cathodic EOF has also been observed in the microchannels composed of native PDMS substrates, which is in agreement with the data of other authors [31,32]. The possible sources of the negative surface charge of native PDMS has recently been discussed [31].…”

supporting

confidence: 92%

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Capillary zone electrophoresis of amino acids on a hybrid poly(dimethylsiloxane)-glass chip

et al. 2005

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Poly(dimethylsiloxane) (PDMS)-PDMS and hybrid PDMS-glass devices have been characterized and compared in terms of current-voltage linearity, contact angle, electroosmotic velocity, electroosmotic mobility, and electrokinetic potential in dependence on the surface treatment. The hybrid PDMS-glass microfluidic devices have further been tested as on-chip capillary electrophoresis systems for the separation of fluorescently labeled amino acids. It has been demonstrated that different methods of surface pretreatment of the PDMS-glass devices result in significantly different separation performance, with plate numbers varying from 650 to 57 000 in dependence on the surface state and the nature of the amino acids. Electrophoretic separations of amino acids have been achieved within tens of seconds with detection limits of less than 2 microM (approximately 2 x 10(-16) to 2.5 x 10(-16) mol quantities at injection volumes of 110-120 pL). The detected amounts of fluorescein isothiocyante (FITC)-amino acids are at least ten times lower, since the amino acid:FITC ratio is 10:1 mol. The results demonstrate the perspective of such hybrid PDMS-glass microfluidic systems and the methods to modify their surfaces for on-chip separation methods for biomolecules.

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supporting

confidence: 92%

“…These experiments indicate the negative zeta-potentials for all the systems studied. Cathodic EOF was also reported by another group [32]. The inconsistency of the data was explained by the differences in the PDMS formulations used.…”

mentioning

confidence: 78%

Capillary zone electrophoresis of amino acids on a hybrid poly(dimethylsiloxane)-glass chip

et al. 2005

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“…Consequently, it seems unlikely that many buffer ions, which tend to be weakly adsorbing, could act as a PDI and control the surface potential. However, the fact that SDS changes the EOF of PDMS, but not glass at pH 9 [28,35], indicates the tendency of hydrophobic compounds to adsorb on PDMS. The similarity of m EOF measured at 1 mM SDS at both pH 3 and 9 is in agreement with observations in polypropylene capillaries with SDS present [36], indicating adsorption of SDS regardless of the surface charge on the polymer.…”

mentioning

confidence: 96%

Electrokinetic control of fluid flow in native poly(dimethylsiloxane) capillary electrophoresis devices

et al. 2000

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Capillary zone electrophoresis (CZE) devices fabricated in poly(dimethylsiloxane) (PDMS) require continuous voltage control of all intersecting channels in the fluidic network in order to avoid catastrophic leakage at the intersections. This contrasts with the behavior of similar flow channel designs fabricated in glass substrates. When the injection plugs are shaped by voltage control and leakage from side channels is controlled by the application of pushback voltages during separation, fluorescein samples give 64 200 theoretical plates (7000 V separation voltage, E = 1340 V/cm). Native PDMS devices exhibit stable retention times (± 8.6% RSD) over a period of five days when filled with water. Contact angles were unchanged (± 1.9% RSD) over a period of 16 weeks of dry storage, in contrast to the known behavior of plasma‐oxidized PDMS surfaces. Electroosmotic flow (EOF) was observed in the direction of the cathode for the buffer systems studied (phosphate, pH 3—10.5), in the presence or absence of hydrophobic ions such as tetrabutylammonium or dodecyl sulfate. Electroosmotic mobilities of 1.49 × 10—5 and 5.84 × 10—4 cm2/Vs were observed on average at pH 3 and 10.5, respectively, the variation strongly suggesting that silica fillers in the polymer dominate the zeta potential of the material. Hydrophobic compounds such as dodecyl sulfate and BODIPY® 493/503 adsorbed strongly to the PDMS, indicating the hydrophobicity of the channel walls is clearly problematic for CZE analysis of hydrophobic analytes. A method to stack multiple channel layers in PDMS is also described.

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“…The results can be seen in Figure 3 and Table 111. The decrease in EOF velocity due to the greater viscosity of the mobile phase and to the decrease in voltage led to an increase in solute retention time and, consequently, in the time of analysis [25]. After an.…”

Section: Results and Discussion Influence Of Buffer Compositionmentioning

confidence: 99%

“…Since the overall net charge of each solute primarily affects its mobility in CE, pH has a significant influence on retention The mobility of each solute increases at high pH; thus in MECC the effective mobility toward the cathode decreases and elution times become longer. Moreover, the degree of dissociation of the capillary surface silanols (the main source generating the zeta-potential) depends strongly on the pH of the buffer solution [25]. We previously demonstrated this influence on the resolution of the nucleotide-3'-monophosphates; at pH 7, we were able to separate the nucleotide-5'-monophosphates, but not the 3'-monophosphates.…”

Section: Influence Of Buffer Compositionmentioning

confidence: 94%

Separation of nucleosides and nucleotide‐3′‐monophosphates by micellar electrokinetic capillary chromatography

Lecoq

Montanarella

Biase³

1993

J Microcolumn Separations

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Abstract. Simultaneous separation of ionic and neutral compounds in micellar electrokinetic capillary chromatography (MECC) is a consequence of a combination of charge/mass ratios, hydrophobicity and charge interactions at the surface of the micelles. The type of resolution can be chosen mainly by modification of the buffer composition and pH. Reproducibility depends on the capillary tubing characteristics, operating conditions, and temperature effects. We report here on the different buffer compositions, pH, temperature, operating conditions, and capillary tubing treatments for the optimal separation and best reproducibility of deoxynucleosides and deoxynucleotide-3'-monophosphates. The effects of different buffer compositions were tested when operating in a constant current mode at 38 pAmps. Lithium phosphate buffer improved the separation speed with little loss in resolution. The best concentration was found to be 20 mM. A concentration of 5 % acetonitrile substantially improved the efficiency of the nucleoside peaks and therefore their resolution. The optimum SDS concentration was found to be at 100 mM. The pH has a significant influence on retention time and resolution, and was adjusted for maximum resolution at pH 9.6. Capillary surface treatments were also investigated. Effective heat dissipation occurred below an operating voltage of 15 kV, and a temperature of 35°C was found to give a good compromise between efficiency, resolution, and time of analysis. Time of analysis can be decreased by using higher operating voltages without compromising the resolution. Efficiencies were 350,000 and 235,000 plates m-l for the nucleosides and nucleotides, respectively. The reproducibility of retention times was good with coefficients of variation below 1 %, which allows the possibility for automatic fraction collection.

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The influence of surface treatments on the electroosmotic flow in micellar electrokinetic capillary chromatography

Cited by 18 publications

References 35 publications

Capillary zone electrophoresis of amino acids on a hybrid poly(dimethylsiloxane)-glass chip

Capillary zone electrophoresis of amino acids on a hybrid poly(dimethylsiloxane)-glass chip

Electrokinetic control of fluid flow in native poly(dimethylsiloxane) capillary electrophoresis devices

Separation of nucleosides and nucleotide‐3′‐monophosphates by micellar electrokinetic capillary chromatography

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