Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Patent
1996-03-20
2000-07-18
Beisner, William H.
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
204601, 252353, 252355, 252356, G01N 2726, G01N 27447
Patent
active
060902507
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention is in the field of chromatography. In particular, the invention relates to improvements in the separation of chiral compounds by micellar electrokinetic capillary chromatography.
BACKGROUND ART
Capillary electrophoresis ("CE") is a well known separation technique that is of increasing interest to those concerned with separations. It is a modification of electrophoresis, typically practiced in a thin glass capillary instead of on a 2-dimensional surface such as paper or in a gel. This technique offers the benefits of high efficiency and resolution, rapid separations, the ability to analyze small sample amounts, and a desirable simplicity from the point of view of the apparatus required when compared to competing analytical techniques such as gel electrophoresis, gas chromatography, and liquid chromatography. As in all separation systems high resolution is the end objective and as in other systems resolution is a function of efficiency (theoretical plates) and selectivity (Weinberger, R. "Practical Capillary Electrophoresis", Academic Press, San Diego, Calif. 1993).
The benefits of capillary electrophoresis derive to a large extent from the use of narrow diameter capillary tubes, which permit efficient removal of the heat generated in the separation process. This heat removal prevents convective mixing which would degrade the separating power. The narrow diameter tubes also allow high voltages to be used to generate the electric field in the capillary while limiting current flow and hence heat generation.
A CE separation begins by filling the capillary with a supporting electrolyte. Next, a small amount of sample is injected into one end of the capillary. Typical sample injection volumes range from 1-20 nanoliters. After sample injection, a high voltage is applied to the capillary and the sample components are separated on the basis of different charge/mass ratios. A capillary electrophoretic separation can also be augmented with a bulk fluid flow, called electroosmotic flow. If present, it moves all components through the capillary tube at the same rate, and generally does not contribute to the resolution of different sample components. Eventually, the sample components move through an appropriate detector, such as a UV detector. This can provide detection and quantitation of each separated sample zone.
A micelle is a colloidal particle formed from surfactant molecules. The practice of capillary electrophoresis in the presence of micelles is commonly referred to as micellar electrokinetic chromatography (Terabe, S., Otsuka, K., Ichikawa, K., Tsuchiya, A. and Ando, T. Analytical Chemistry, 1984, (56) 111-113; Terabe, S., Otsuka, K., and Ando, T. Analytical Chemistry, 1985, (57)834-841). This term will be used to refer to both micellar electrophoretic separations, (separations where the electroosmotic flow is negligible), and micellar electrokinetic separation (separations where the electroosmotic flow impacts the separation time). The equations for retention and resolution in MEKC are shown as equations 1 and 2 (Terabe, S., et al. supra). ##EQU1## where t.sub.r =retention time of the solute t.sub.o =retention time of solute in the absence of micelles ##EQU2## where N=efficiency (theoretical plates) .alpha.=selectivity.
Equation 3 is the resolution equation for HPLC, with all terms as previously defined. ##EQU3##
The resolution equation for MEKC is very similar to the resolution equation for HPLC. In fact, as t.sub.mc approaches infinity, the equations become identical (equation 3). Considering the case where t.sub.mc or t.sub.o equals infinity, one can easily se the difference between HPLC and MEKC. The practical difference between HPLC and MEKC is related to the efficiency term of the resolution equation. In HPLC a typical value of N (theoretical plates) is 5000 while a typical value of N for MEKC is 100,000. In quantitative terms a widely accepted goal for resolution of two peaks is a value of 1.5. Assuming k'=1, then the resolution requirement of 1.5 requires an alpha val
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Soini, Helena et al., "C
Grover Edward R.
Mazzeo Jeffrey R.
Merion Michael
Petersen John S.
Swartz Michael E.
Beisner William H.
Starsiak Jr. John S.
Waters Investments Limited
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