Silica electrokinetics

Lee et al. [30] described a micellar electrokinetic capillary chromatographic method for the determination of some antiepileptics including valproic acid. They used a fused silica capillary column (72 cm x 50 pm) and SDS as the micellar phase and multiwavelength UV detection. Reaction conditions, such as pH and concentration of running buffer were optimized. Solutes were identified by characterizing the sample peak in terms of retention time and absorption spectra. Recoveries were 93-105%. 

Fig. 15. Electrochromatograms obtained in columns coated with sol-gel composites (A) TEOS and (B) C8-TEOS/TEOS. (Reprinted with permission from [80]. Copyright 1999 American Chemical Society). Separation conditions fused silica capillary, 12 pm i.d., 60 cm total length, 40 cm active length, mobile phase 60/40 methanol/1 mmol/1 phosphate buffer, voltage 30 kV, electrokinetic injection 5 s at 6 kV, UV detection at 214 nm. Peaks toluene (1), naphthalene (2), and biphenyl (3)...

Dolezalova, M., Capova, H., and Jobanek, R. (2003). Determination of the purity of phenoxymethylpenicillin by micellar electrokinetic chromatography and reversed phase liquid chromatography on a monolithic silica column.. Sep. Sci. 26, 701—708. 

Efforts toward integrating SPE onto a lab-on-a-chip device are currently being investigated by the Collins group. Two complementary approaches are being pursued. One approach is to use small-diameter, Cl8 functionalized silica beads that are packed into a microchannel to form an extraction bed [46], A sample solution containing trace levels of explosives is electrokinetically directed across the microcolumn bed, causing the hydrophobic explosive molecules to adsorb onto the stationary phase with nearly 100% efficiency. Subsequently,... 

The glass fibers and fused-silica glass (Thermal American Fused Quartz Co.) were crushed and then dispersed in water. The pH of this near-neutral suspension was varied using KOH or HNO,. In some experiments, a hydrolyzed solution of y-APS was added to this suspension. Here, the initial pH was 10. The electrophoretic mobilities of glass fragments suspended in these solutions were measured without any further treatment except for the addition of electrolyte (10-3 M KNO,). These analyses were performed using a Rank Brothers Particle Micro-Electrophoresis Apparatus Mark II or a Pen Kem System 3000 Automated Electrokinetics Analyzer. 

Eberle et al. [134] separated the enantiomers of omeprazole and structurally related drugs by capillary zone electrophoresis with bovine serum albumin as chiral selector. The separations were carried out on a fused silica column (60 cm x 50 pm, 50 cm to detector) with a buffer consisting of 100-/zM-bovine serum albumin and 7% 1-propanol in 10 mM potassium phosphate pH 7.4. Electrokinetic injection was at 5-8 kV for 7 s. An applied voltage of 300 V/cm was used. Detection was at 290 nm. Detection limits were 0.04 mg/ml for the analytes studied. 

Capillary electrophoresis separation is performed in a flexible fused silica capillary tube that is filled with an appropriate buffer solution of defined pH and ionic strength (aqueous/nonaqueous). A small volume of sample (lower than 3-4% of the column volume) is needed to achieve efficient separation. This volume is introduced hydrodynamically (or less often electrokinetically) into the capillary to which an electrical potential is applied (Figure 13.7). Charged species of the sample exhibit... 

This electrokinetically driven micro mixer uses localized capacitance effects to induce zeta potential variations along the surface of silica-based micro channels [92], The zeta potential variations are given near the electrical double layer region of the electroosmotic flow utilized for species transport. Shielded ( buried ) electrodes are placed underneath the channel structures for the fluid flow in separate channels, i.e. they are not exposed to the liquid. The potential variations induce flow velocity changes in the fluid and thus promote mixing [92],... 

One key feature of CE is the overall simplicity of the instrumentation. Briefly, the ends of a narrow-bore, fused silica capillary (25-75 pm i.d., 350-400 pm o.d., and 10-100 cm in length) are placed in buffer reservoirs. The content of the reservoirs is identical to that within the capillary. The reservoirs also contain the electrodes used to make electrical contact between the high voltage power supply and capillary. The sample is loaded into the capillary as follows one of the reservoirs (usually at the anode) is replaced by the sample reservoir and either an electric field (electrokinetic... 

Fig. 10.1. Separation of polycyclic aromatic hydrocarbons (PAHs) on columns packed with Spherisorb ODS particles. Conditions (A) 35(43) cm x 50 pm i.d. fused silica capillary column packed with 3 pm Spherisorb ODS-1 particles (B) 41(53) cm x 75 pm i.d. fused-silica capillary column packed with 5 pm Spherisorb ODS-1 particles 30 kV applied voltage 5 kV, 5 s electrokinetic injection acetonitrile-50 mM Tris buffer, pH 8.1 (80 20 v/v). Peak identifications 1, benzene 2, naphthalene 3, acenaphthylene 4, fluorene 5, acenaphthene 6, phenanthrene 7, anthracene 8, fluoranthene 9, pyrene 10, benz[n]anthracene 11, chrysene 12, benzo[6]fluoranthene 13, benzo[fc]fluoranthene 14, benzo[a]pyrene 15, dibenz[n,/i]anthracene 16, indeno[7,2,3-af]pyrene 17,...

Fig. 10.2. Separation of a mixture of PAHs on reversed-phase capillaries (a) without and (b) with silicate entrapment. Conditions 75 pm i.d. fused-silica capillary packed with 5 pm Nucleosil ODS particles column effective lengths 25 cm for the non-entrapped column and 17 cm for the entrapped column. Both electrochromatograms were obtained under the same conditions mobile phase, acetonitrile-0.1 M acetate buffer, pH 3.0, 80 10 (v/v) applied voltage 30 kV UV detection at 254 nm 20°C pressure 9 bar applied to both vials electrokinetic injection, 10 kV for 10s. Reproduced with permission from Chirica and Remcho [10].

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