Electrokinetic voltage

Recently, CE coupled with Ru(bpy)3 ECL for highly sensitive detection of metformin hydrochloride (MH) derivatized with acetaldehyde is reported. The precolumn derivatization of MH with acetaldehyde was performed in phosphate buffer solution (0.3 mol L pH 7.5) at room temperature for 120 min. The factors affecting this method of analysis, e.g., acetaldehyde concentration, buffer pH, electrokinetic voltage and injection time were examined and under optimization of these conditions, the MH ECL detection sensitivity was more than 120 times that without derivatization. The detection of 0.3 ng mL with S/N = 3 was attained. The proposed method is simple, economical, and sensitive and is used for the determination of MH in urine [42]. A method combining CE with Ru(bpy)3 " ECL detection that can be applied to amine-containing clinical species was developed, and the performance of CE-ECL as a quantitative method for the determination of sulpiride in human plasma or urine was evaluated [43]. 

The electrokinetic effect is one of the few experimental methods for estimating double-layer potentials. If two electrodes are placed in a coUoidal suspension, and a voltage is impressed across them, the particles move toward the electrode of opposite charge. For nonconducting soHd spherical particles, the equation controlling this motion is presented below, where u = velocity of particles Tf = viscosity of medium V = applied field, F/cm ... 

Electrokinetic (also called electromigration) injection is performed by placing the inlet of the capillary and an electrode in the sample vial. Following this a voltage is applied during a defined period of time. The sample constituents are actively carried into the capillary, and when present, the EOF also passively carries them into the capillary. For this reason, neutral compounds are also injected. The active migration is due to the effective electrophoretic mobilities of the constituents. The amount (B), in units of concentration injected into the capillary is expressed by [2,38]... 

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)...

The washing of capillaries with dilute alkaline solution is advisable before analysis. The alkaline solution can be followed by deionized water and buffer. Capillaries can be washed between runs too. Samples can be introduced into the capillary by hydrodynamic and electro-kinetic methods. The hydrodynamic method applies a pressure difference (5-10 sec) between the two ends of the capillary. The pressure difference can be achieved by overpressure, vacuum or by creating a height difference between the levels of the buffer and sample reservoirs. In the case of electrokinetic injection, the injection end of the capillary is dipped into the sample for a few seconds and a voltage of some thousand volts is applied. 

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].

In electrophoretic injection, the capillary inlet is immersed in the sample solution and a voltage is applied for a determined period of time. The amount of sample introduced into the capillary depends on the voltage and the time it was applied. Sample injection is a compromise between detection and resolution, and its parameters are often best determined experimentally. If detection is not a problem, resolution can be greatly improved by maintaining the sample plug as narrow as possible. If EOF is present, sample ions will be introduced by a combination of electrophoretic mobility and EOF under these conditions, this injection mode is generally termed electrokinetic injection. 

Electrokinetic injection involves using voltage to inject sample onto the capillary. The sample serves as a buffer reservoir (Figure 1). A voltage is applied and the analyte(s) migrate onto the capillary. The amount of material injected is dependent on the mobility of the analyte(s). The quantity injected is given by... 

Injection mode (e.g., electrokinetic, hydrodynamic), parameters (e.g., voltage, pressure, time)... 

Figure 13.9 Microchip-based micellar electrokinetic chromatography (MEKC) electro-pherogram of a mixture of nitroaromatics and nitramines. Analytes 20 ppm of each (1) TNB, (2) DNB, (3) NB, (4) TNT, (5) tetryl, (6) 2,4-DNT, (7) 2,6-DNT, (8) 2-, 3-, and 4-NT, (9) 2-Am-4,6-DNT, (10) 4-Am-2,6-DNT. Conditions MEKC buffer, 50 mM borate, pH 8.5, 50 mM SDS, 5 M Cy7, separation voltage 4 kV, separation distance 65 mm. (Reprinted in part with permission from [37]. Copyright 2000 American Chemical Society.)...

Fig. 9 Electropherograms showing 3 nM fluorescently labeled 11-mer in the absence (A) and in the presence (B) of 0.7 /j,M SSB protein in the running buffer. The conditions used were as follows separation capillary, 35 cm, 20-/xm i.d. running buffer, 25 mM disodium tetraborate (pH 9.1) separation voltage, 25 kV excitation wavelength, 488 nm emission wavelength, 515 nm and temperature, 25 (1°C. Approximately 1 nL of sample solution was injected electrokinetically. The asterisk indicates the migration time of the solvent, The traces Iv and Ih, corresponding to vertically and horizontally polarized fluorescence intensities, respectively, are shown separated for clarity. (From Ref. 48.)...

For electrokinetic injection, the capillary is dipped in the sample and a voltage is applied between the ends of the capillary. The moles of each ion taken into the capillary in t seconds are... 

Fig. 15 Separation of ropivacaine and propranolol enantiomers using an MIP plug composed of (S)-ropivacaine MIP and (S)-propranolol MIP. The capillary was 100 cm in total length and 91.5 cm in effective length. The electrolyte contained acetonitrile/2 mol L-1 acetic acid adjusted to pH 3 by the addition of triethanolamine (90/10, v/v). The separation voltage was 15 kV, and the capillary column was thermostated to 60 °C. The MIPs were injected hydrodynamically at 50 mbar for 6 s each, and the sample was composed of 50 pmol L 1 rac-propranolol (first eluting) and rac-ropivacaine injected electrokinetically at 16 kV for 3 s. Detection was performed at 214 (top) and 195 nm (bottom) [42]...

Separation and injection in electrophoresis microchips is electrokinet-ically driven using high voltages. The high voltage applied for the... 

Separation and injection in the microchip is driven electrokinetically using high voltages. The different steps are ... 

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