Capillary separations, applications

Kasicka, V., Pruslk, Z., Sazelova, P., Jiracek, J. and Barth, T., Theory of the correlation between capillary and free-flow zone electrophoresis and its use for the conversion of analytical capillary separations to continuous free-flow preparative processes. Application to analysis and preparation of fragments of insulin, ]. Chromatogr. A, 796, 211, 1998. 

General applications While capillary separation methods produce peak capacities, n, numbered in hundreds, many real-world mixtures (e.g. in the petroleum industry) require values of 104. This can only... 

Factors Affecting Ionic Migration. Effect of Temperature. pH and Ionic Strength. Electro-osmosis. Supporting Medium. Detection of Separated Components. Applications of Traditional Zone Electrophoresis. High-performance Capillary Electrophoresis. Capillary Electrochromatography. Applications of Capillary El ectrochromatography. ... 

Biomolecular MS and in particular MALDI-TOF-MS (see Sections 2.1.22 and 2.2.1) permit the routine analysis of oligonucleotides up to 70-mers, intact nucleic acids, and the direct detection of DNA products with no primer labels with an increase in analysis speed and mass accuracy especially in contrast to traditional DNA separation techniques such as slab gels or capillary electrophoresis. Applications focus on the characterization of single nucleotide polymorphisms (SNPs) and short tandem repeats (STRs). Precise and accurate gene expression measurements show relative and absolute numbers of target molecules determined independently of the number of PCR cycles. DNA methylation can be studied quantitatively. 

F Lelievre, P Gareil, A Jardy. Selectivity in capillary electrophoresis application to chiral separations with cyclodextrins. Anal Chem 69 385—392, 1997. 

Applications of LC-NMR are still scarce but the technique will become more widely used. The main effort for efficient exploitation of LC-NMR needs to be made on the chromatographic side, where strategies involving efficient preconcentration, high loading, stop-flow, time slicing, or low flow procedures have to be developed. Microbore columns or capillary separation methods, such as capillary LC-NMR, CE-NMR, and CEC-NMR, will find increased application, one reason being that the low solvent consumption will allow the use of fully deuterated solvents. 

The types of hollow fiber membranes in production are illustrated in Figure 3.32. Fibers of 50- to 200-p.m diameter are usually called hollow fine fibers. Such fibers can withstand very high hydrostatic pressures applied from the outside, so they are used in reverse osmosis or high-pressure gas separation applications in which the applied pressure can be 1000 psig or more. The feed fluid is applied to the outside (shell side) of the fibers, and the permeate is removed down the fiber bore. When the fiber diameter is greater than 200-500 xm, the feed fluid is commonly applied to the inside bore of the fiber, and the permeate is removed from the outer shell. This technique is used for low-pressure gas separations and for applications such as hemodialysis or ultrafiltration. Fibers with a diameter greater than 500 xm are called capillary fibers. 

Carabias-Martinez, R., E. Rodriquez-Gonzalo, J. Dominquez-Alvarez, and J. Hemandez-Mendez (2002). Comparative study of separation and determination of triazines by micellar electrokinetic capillary chromatography and nonaqueous capillary electrophoresis Application to residue analysis in natural waters. Electrophoresis, 23 494—501. 

Counterflow modules are always more efficient than crossflow modules, but the advantage is most noticeable when the membrane selectivity is much higher than the pressure ratio across the membrane and a significant fraction of the most permeable component is being removed from the feed gas. This is the case for air-dehydration membrane modules, so counterflow capillary modules are almost always used. With most other gas-separation applications, the advantage offered by counterflow designs does not offset the extra cost of making the counterflow type of module, so they are not widely used. 

A review of capillary electrophoresis applications in pharmaceutical analysis was published in 1993, and the goal of this chapter is to provide an update on the various disciplines within the technique and includes selected applications. Recent developments in the areas of capillary technology, instrumentation, and detection will be reviewed here. Useful strategies for method development involving several classes of pharmaceuticals and biotechnology products will be addressed. The formats within capillary electrophoresis have evolved to such an extent that this chapter is not comprehensive in scope. Therefore, the reader will be directed to other reviews on the various aspects of capillary electrophoresis. Of particular interest to many separation scientists may be a special issue of an Applied Biosystems Newsletter, which addresses the future role of CE, method development in CE, and selected applications in the area of drug analysis and protein separations [7]. 

Sample collection and preparation are crucial issues for any bioanalytical application in order to address the complexity of samples originating from biological tissues and fluids. It is necessary to cope with the lack in concentration sensitivity typical for capillary separation techniques, to avoid interference from matrix components as well as to ensure analyte stability. In peptide analysis, a strong focus exists on handling small-volume samples and on selective concentration of the analyte in order to overcome limitations with respect to loadability. In addition, loss of analyte frequently occurs due to degradation by proteases and due to adsorption to surfaces, which accordingly needs to be minimized. 

Figure 12.13 shows such a separation, using a 40 cm, 75 pm uncoated fused silica capillary operated at 30 kV. A solution of ampholytes (5%) and sample (1 mg/mL of each protein) in the running buffer are loaded throughout the capillary. The application of the electric field results in slow, continuous separation and detection due to the slow electroosmotic flow. With this method, no salt mobilization is required. 

A Karbaum, T Jira. Nonaqueous capillary electrophoresis Application possibilities and suitability of various solvents for the separation of basic analytes. Electrophoresis 20 3396-3401, 1999. 

Online coupling of HPLC with nuclear magnetic resonance spectroscopy (NMR) has proved useful for a wide range of applications. The shortcoming of suppression of eluent signals can be circumvented by use of capillary separation technique. In this mode detection cells with internal volumes in the nanoliter scale and miniaturized probe heads have been developed by Albert et al. in Tuebingen. The system can be used in either HPLC, CE, or CEC, and consists of a capillary inserted into a 2.5 or 2.0 mm NMR microprobe equipped with a Helmholtz coil. In experiments, a capillary mbe of 315 /rm can create a detection volume of 900 nl. The flow rate of the capillary... 

Due to the rapidly growing importance of capillary columns in bioanalytical applications, special attention will now be devoted to sampling techniques associated with capillary GC. Small samples are typical for this type of chromatography and, consequently, a direct introduction of such samples is an apparent technological problem. In most biochemically interesting applications (typically, trace analysis problems), there is no general discrepancy between the demands of such analysis and the performance and sensitivity of capillary separation techniques. However, the manipulation of samples presents difficulties, as reliable methods for measurement, disposal, and introduction of nanoliter volumes are not readily available. Ironically, in many capillary GC applications, the solvent serves only as a sample vehicle we... 

With packed column SFC separations, FT-IR detection can be useful in spectrally resolving components which may not be resolved by the chromatographic column. FT-IR also shows good sensitivity for the smaller quantities of materials encountered with capillary SFC applications. Spectral quality is sufficient for identification and for distinguishing subtle differences between related compounds. 

The CEC-NMR contour plot indicated that all compounds are base-lined separated resulting in distinct NMR rows in the 2D display. This example shows the high application power of CE and CEC-NMR for providing unambiguous information about substances in complex organic molecules. The first steps towards a high-throughput separation system have already been made. For the successful performance of real-world applications, NMR sensitivity must be improved. NMR probes with 1-ng sensitivity should facilitate the application of capillary separations for metabolite structure elucidation and functional food analysis. 

Summarizing this chapter, it can be stated that the linking of NMR spectrometers (from 400 to 750 MHz) to various separation techniques has been developed into rather a powerful tool. Stereochemical problems in metabolism studies can be easily solved if the concentration of the present compounds is above the detection threshold. The coupling of capillary separation techniques together with NMR detection will stimulate high-throughput screening applications in modem dmg development. 

If there are no previous published methods for a particular pharmaceutical compound or class of compound then evaluation of some of the properties and functionalities must be considered to determine the initial method conditions. If pAia data are available for the solute of interest and other species that need to be resolved then an appropriate electrolyte pH can be selected. If the compound is present as a racemic mixture then selection of an appropriate chiral selector can be made based on the compounds functional groups and other chiral separation applications. For basic compounds, a 50 mM phosphate (Na2HP04) buffer adjusted to pH 2.5 with phosphoric acid, in a standard capillary with an applied voltage of +20 kV and UV detection at 200 nm is a good starting point. 

Kostal, V., Zeisbergerova, M., Urotekova, Z., Slais, K., and Kahle V., Miniaturized liquid core waveguide-based fluorimetric detection cell for capillary separation methods Application in CE of... 

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