Capillary electrophoresis electrokinetic injection

There are two modes of injection in capillary electrophoresis hydrodynamic injection and electroki-netic injection. In hydrodynamic injection, pressure or vacuum are plaeed on the inlet sample vial or the outlet waste vial, respeetively. For electrokinetic injection, the voltage is activated for a short time with the capillary and electrode immersed in the sample. 

Keywords Capillary electrophoresis Micellar electrokinetic chromatography Microchip pTAS Nonaqueous capillary electrophoresis How injection analysis Solid-phase microextraction Bipolar electrochemical swimmers... 

Injecting the Sample The mechanism by which samples are introduced in capillary electrophoresis is quite different from that used in GC or HPLC. Two types of injection are commonly used hydrodynamic injection and electrokinetic injection. In both cases the capillary tube is filled with buffer solution. One end of the capillary tube is placed in the destination reservoir, and the other is placed in the sample vial. 

FIGURE 15.1 One-dimensional capillary electrophoresis separation of a protein homogenate prepared from the hTERT cell line. Both separations were preformed in 30 pm ID, 145 pm OD, 20 cm long capillaries at 20,000 V. (a) Micellar electrokinetic chromatography performed with a 100 mM CHES, 100 mM Tris, and 15 mM SDS buffer at pH 8.7. Sample is electro-kinetically injected with 0.25 kV for 1 s (b) Capillary sieving electrophoresis performed in 5% Dextran (513 kDa), 100 mM CHES, 100 mM Tris, 3.5 mM SDS, pH 8.7. 

Fig. 3.172. Non-aqueous capillary electrophoresis with electrochemical detection of a dye mixture containing (a) 1.7 jUg/ml malachite green, (b) 0.70 jug/ml crystal violet, (c) 4.3 /ig/ml rhodamine B, and (d) 9.1 X 10-6 M ferrocene. Experimental conditions capillary dimensions, 95 cm X 75 pm i.d. running electrolyte, acetonitrile containing 1 M HAc and 10 mM NaAc electrokinetic injection, 20 s 5 kV separation voltage 20 kV applied detection potential, 1.55 V. Reprinted with permission from F.-M. Matysik [206].

Figure 26-26 Lower trace Sample injected electrokinetically for 2 s without stacking is limited in volume to prevent band broadening. Upper trace With stacking. 15 times more sample could be injected (for 30 s). so the signal is 15 times stronger with no increase in bandwidth. [From V Zhao and C. f. Lurie, pH-Mediated Field Amplification OmCotumn Preconcentration of Anions in Physiological Samples for Capillary Electrophoresis, Anal. Chem. 1999, 71,3985.]...

J. Palmer, N. J. Munro, and J. P. Landers, A Universal Concept for Stacking Neutral Analytes in Micellar Capillary Electrophoresis, Anal. Chem. 1999, 71, 1679 J. Palmer, D. S. Burji, N. J. Munro, and J. P. Landers, Electrokinetic Injection for Stacking Neutral Analytes in Capillary and Microchip Electrophoresis, Anal. Chem. 2001, 73, 725 J. P. Quirino, S. Terabe, and... 

Figure 9.7 Schematic illustration of the flow-gating interface. A channeled Teflon gasket was sandwiched between two stainless steel plates to allow for flow into the electrophoresis capillary, either from the flush buffer reservoir or from the LC microcolumn during an electrokinetic injection.

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. 

Palmer, J., Burgi, D.S., Munro, N.J., Landers, J.P., Electrokinetic injection for stacking neutral analytes in capillary and microchip electrophoresis. Anal. Chem. 

Capillary electrophoresis separations are dependent on the relative mobilities of analytes under the influence of an electric field and do not depend on mobile phase/stationary phase interactions. A fused silica capillary is filled with a buffer and both ends submerged into two reservoirs of the buffer. A platinum electrode is immersed in each reservoir and a potential difference (5-30 kV) is applied across the electrode. An aliquot of sample of a few nanoliters is injected onto the capillary by either hydrostatic or electrokinetic injection, and the components migrate to the negative electrode. Separations of analytes arise from differences in the electrophoretic mobilities, which are dependent on the mass-to-charge ratio of the components, physical size of the analyte, and buffer/analyte interactions. An electro-osmotic flow (EOF) of the buffer occurs in the capillary and arises as a result of interactions of the buffer with dissociated functional groups on the surface of the capillary. Positive ions from the buffer solution are attracted to negative ions... 

Kappes et al. evaluated the potentiometric detection of acetylcholine and other neurotransmitters through capillary electrophoresis [209]. Experiments were performed on an in-house capillary electrophoresis instrument that made use of detection at a platinum wire, dip-coated in 3.4% potassium tetrakis (4-chlorophenyl) borate/64.4% o-nitrohenyl octyl ether/32.2% PVC in THF. The results were compared to those obtained using capillary electrophoresis with amperometric detection at a graphite electrode. Samples prepared in the capillary electrophoresis buffer were electrokinetically injected (7 s at 5 kV) into an untreated fused silica capillary (88 cm x 25 pm i.d.) and separated with 20mM tartaric acid adjusted to pH 3 with MgO as the running buffer. The system used an applied potential of 30 kV, and detection versus the capillary electrophoresis ground electrode. 

Capillary electrophoresis of PCR-amplified products is usually performed in the reverse polarity mode (negative potential at the injection end of the capillary). A coated capillary (100 mm i.d., 37-57 cm total length) is filled with a gel buffer system. PCR samples are introduced hydrodynamically or, after desalting, electrokinetically. The PCR sample and a DNA marker of known size may be injected sequentially and allowed to comigrate in the capillary. With a capillary temperature set at 20 to 30°C, separation of PCR products is accomplished at field strengths of 200 to 500 V/cm. Detection is on-line, measuring either UV absorbance at 260 nm, or LIF. 

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