Methods of Analyte Concentration in a Capillary
Online sample concentration techniques in capillary electrophoresis separations have rapidly grown in popularity over the past few years. During the concentration process, diluted analytes in long injected sample are concentrated into a short zone, then t
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Methods of Analyte Concentration in a Capillary Paweł Kubalczyk and Edward Bald
Abstract Online sample concentration techniques in capillary electrophoresis separations have rapidly grown in popularity over the past few years. During the concentration process, diluted analytes in long injected sample are concentrated into a short zone, then the analytes are separated and detected. A large number of contributions have been published on this subject proposing many names for procedures utilizing the same concentration principles. This chapter brings a unified view on concentration, describes the basic principles utilized, and shows a list of recognized current operational procedures. Several online concentration methods based on velocity gradient techniques are described, in which the electrophoretic velocities of the analyte molecules are manipulated by field amplification, sweeping and isotachophoretic migration, resulting in the online concentration of the analyte. Capillary electrophoresis (CE) is a modern analytical technique which allows a fast and effective separation of charged particles present in a very small sample. Separation is based on differences in electrophoretic ionic mobility in the electric field, in a narrow capillary [1–12]. CE combines advantages offered by two techniques that constitute the foundation stones upon which modern bio-analysis was built: high performance liquid chromatography and conventional gel electrophoresis (SGE). CE is usually more efficient than any of the two techniques applied separately [13]. When optimizing the electrophoretic conditions in CE, one of many challenges to meet is to lower the limit of detection (LOD) expressed in a number of concentration units. High LOD results from two factors: limited optical path in the most popular CE detection in a capillary and a small volume of a sample which P. Kubalczyk (&) E. Bald Faculty of Chemistry, University of Łódz´, Łódz´, Poland e-mail: [email protected]
B. Buszewski et al. (eds.), Electromigration Techniques, Springer Series in Chemical Physics 105, DOI: 10.1007/978-3-642-35043-6_12, Ó Springer-Verlag Berlin Heidelberg 2013
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can be injected into the capillary [14]. The optimum volume of the sample applied should not exceed 1–3 % of the capillary volume. The injection of a bigger amount of the sample causes the so-called capillary overload, the result of which is broadening the bands and significantly deteriorated resolution. Additionally, in order to obtain high performance and short analysis time, it is essential to use capillaries of small internal diameters (25–100 lm). Since the capillary cross section is round, the real optical path length is reduced to 80 % of the internal diameter [15]. Low sensitivity is perceived as one of the main limitations of electrophoretic separation methods, particularly when compared to traditional liquid chromatography techniques [16]. The detection limits of the same substances analyzed by means of electromigration techniques are usually 10–100
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