Capillary electrophoresis plate number

Efficiency The efficiency of capillary electrophoresis is characterized by the number of theoretical plates, N, just as it is in GC or ITPLC. In capillary electrophoresis, the number of theoretic plates is determined by... 

Muzikar, J. van de Goor, T. Kenndler, E. The Principle Cause for Lower Plate Numbers in Capillary Zone Electrophoresis with Most Organic Solvents. Anal. Chem. 2002, 74, 434-439. 

TH Seals, C Sheng, JM Davis. Influence of neutral cyclodextrin concentration on plate numbers in capillary electrophoresis. Electrophoresis 22 1957-1973, 2001. 

The observed behavior of benzyl alcohol (C6H5CH2OH) in capillary electrophoresis is given here. Draw a graph showing the number of plates versus the electric field and explain what happens as the field increases. 

There is much interest in high-efficiency- and high-speed separation media for liquid chromatography. The plate numbers available in practice have been in the range of 10,000-30,000 in HPLC for 20 years or so, but these are low compared to well over 100,000 theoretical plates in capillary gas chromatography or in capillary electrophoresis. This is caused by the limitation in the use of small-sized particles for HPLC, where a particle-packed column is commonly used under a pressure-drop of up to 40 MPa. An increase in column efficiency by using small particles, which is the approach taken in the past, is accompanied by an increase in the pressure-drop, as expected from Eqns. 5.2 and 5.3, below. Eqns. 5.1-3 describe the efficiency (plate height) and flow resistance of a column packed with particles [1-3], where N stands for the... 

At times, capillary electrophoresis is called high-performance capillary electrophoresis to reflect the high number of theoretical plates offered by this technique as a result, superior resolution is possible. The original contribu-tor(s) to high-performance capillary electrophoresis and the basis of separation in various modes are shown in Table 2.4 9... 

In capillary gel electrophoresis, one of the major contributors to band broadening, besides the injection and detection extra-column effects, is the longitudinal diffusion of the solute molecules in the capillary tube [14], The theoretical plate number (N) is characteristic of column efficiency ... 

Ruhr s group studied the separation of double- and single-stranded DNA restriction fragments in capillary electrophoresis with polymer solutions under alkaline conditions in epoxy-coated capillaries and found that at pH 11 the theoretical plate numbers exceeded several millions [96], At pH 12, single-stranded DNA molecules were still well separated in entangled hydroxyethylcellulose (HEC) solutions, but the resolution decreased significantly in dilute polymer solutions. 

There are two important equations which describe the resolution of capillary electrophoresis in terms of the number of theoretical plates, and the migration time for molecules through a column. 

In conclusion, capillary electrophoresis in carbohydrate analysis has advantages in both separation and detection over other techniques of electrophoresis, as well as chromatography. It allows high efficiency (up to a few million plate numbers) and very good sensitivities (up to femtomolar). In addition, CE permits analysis by a variety of separation modes simply by changing the electrolyte (capillary zone electrophoresis, MEKC, CGE). 

For enantioseparation on CSPs in CEC, nonstereospecific interactions, expressed as 4>K, contribute only to the denominator as shown in Eq. (1), indicating that any nonstereospecific interaction with the stationary phase is detrimental to the chiral separation. This conclusion is identical to that obtained from most theoretical models in HPLC. However, for separation with a chiral mobile phase, (pK appears in both the numerator and denominator [Eq. (2)]. A suitable (f)K is advantageous to the improvement of enantioselectivity in this separation mode. It is interesting to compare the enantioselectivity in conventional capillary electrophoresis with that in CEC. For the chiral separation of salsolinols using /3-CyD as a chiral selector in conventional capillary electrophoresis, a plate number of 178,464 is required for a resolution of 1.5. With CEC (i.e., 4>K = 10), the required plate number is only 5976 for the same resolution [10]. For PD-CEC, the column plate number is sacrificed due to the introduction of hydrodynamic flow, but the increased selectivity markedly reduces the requirement for the column efficiency. 

Capillary electrophoresis and its most popular hybrid technique - capillary electrochromatography - are complementary to HPLC, offering rapid analysis, low consumption of sample and solvents, and usually a higher efficiency of separation (due to a larger number of theoretical plates). Similar to HPLC, enantioseparation with the use of electrophoretic methods can be conducted by direct (chiral phase... 

The separation of endogenous 17- or 18-hydroxylated corticosteroids of the 21-hydroxylated 4-pregnen series was obtained by capillary electrophoresis of their charged borate chelate complexes (323). Aldosterone, 18-hydroxycorti-costerone, 18-hydroxy-deoxycorticosterone, cortisone, cortisol and 11-deoxycor-tisol are separated and resolved with 400 mM borate buffer at pH 9.0. The corticosteroid/borate chelation complex as indicated by CE data correlated well with 11 B-NMR. The separation of corticosteroids and benzothiazin analogs were studied by MEKC and a comparison with CZE was made (324). Bile salts, which have a similar carbon skeleton to the corticosteroids, were used for the separation of these steroids. A short analysis time, 15 min, and a high number of theoretical plates (150,000-350,000) were obtained. Sodium cholate was found to be very effective. The MEKC method was applied to the determination of the drug substance in tablets and cream formulations. An internal standard method was used for quantitation. The purity of the drug substance was also determined. 

Capillary electrophoresis and mass spectrometry can be coupled using a special ESI interface that provides an additional makeup flow, comprised of water, organic solvent, and acid, to create suitable conditions for ESI (Figure 2.14). Flow rates and sample loading are very low in CE. The supplemental sheath makeup liquid, while useful in the ESI process, has the effect of diluting the analyte, thereby compounding the sensitivity problem caused by the small amounts of analyte used in CE. The importance of CE is that the very large number of theoretical plates available enable complex separations that can reveal subtle differences in analytes. 

The ionization and net charge of the sample components are affected significantly by changes in the pH of the sample. As a result, the migration rate, the solubility, the theoretical plate number, and the peak height could aU get affected. Proper dilution of the sample with an appropriate buffer is the first step in separation. Usually, the sample is diluted with the same solvent used as the electrophoresis buffer however, in some instances, a pH of the sample different from that of the buffer is selected to concentrate the sample on the capillary (stacking). 

Capillary electrophoresis (CE) is a relatively new analytical technique (for recent reviews, see Kuhr and Monnig, 1992 Weinberger, 1993) in which separations are performed in narrow inside diameter (i.d.) columns (25-100 m) at high field strengths (hundreds of volts per centimeter). This results in a number of advantages that include very high resolution separations (to 10 plates/m) and rapid separation times (<30 min). The commercialization of automated instrumentation has enabled rapid, automated methods development to be performed, employing a number of different separation modes. 

Capillary electrophoresis has several advantages. CE is truly a micromethod and requires only a very small sample. In terms of theoretical plates, CE has at least ten times the separation abiUty of a typical IC system. Separations are fast and a number of experimental conditions can be adjusted to obtain a good separation of difficult samples. 

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