Capillary electrophoresis operating modes

Application 2 Capillary Gel Electrophoresis. Recently, Karger and co-workers demonstrated the use of polyacrylamide gel-filled capillaries to separate peptide/protein (SDS PAGE) Qfi) and oligonucleotide mixtures (12,22) by capillary electrophoresis. This mode of CE operation may prove to couple well with on-line radioisotope detection. The results of several preliminary capillary electrophoresis separations using gel-filled capillaries and on-line radioisotope detection using the coincidence unit described here are presented below. 

In the previously described electrophoretic methods, the capillary was filled with electrolytes only. Another mode of operation in capillary electrophoresis involves filling the capillary with gel or viscous polymer solutions. If desired, a column can be packed with particles and equipped with a frit.68 This mode of analysis has been favorably used for the size determination of biologically important polymers, such as DNA, proteins, and polysaccharides. The most frequently used polymers in capillary gel electrophoresis are cross-linked or linear polyacrylamide,69 cellulose derivatives,70-75 agarose,76 78 and polyethylene glycols. 

Capillary zone electrophoresis (CZE) is the most common electrophoretic separation technique due to its simplicity of operation and its flexibility. It is the standard mode for drug analysis, identification of impurities, and pharmacokinetic studies. Other separation modes, such as capillary isotachopho-resis (CITP), micellar electrokinetc chromatography (MEKC), capillary electrochromatography (CEC), capillary gel electrophoresis (CGE), capillary isoelectric focusing, and affinity capillary electrophoresis (ACE), have then-advantages in solving specific separation problems, since the separation mechanism of each mode is different. 

Currently, there are five major modes of operation of CE capillary zone electrophoresis (CZE), also referred to as free solution or free flow capillary electrophoresis micellar electrokinetic chromatography (MEKC) capillary gel electrophoresis (CGE) capillary isoelectric focusing (CIEF) and capillary isotachophoresis (CITP). Of these, the most commonly utilized capillary techniques are CZE and MEKC (Rabel and Stobaugh 1993 Issaq 1999 Smyth and McClean 1998). 

We report here the design and characterization of three simple, on-line radioisotope detectors for capillary electrophoresis. The first detector utilizes a commercially available semiconductor device responding directly to 7 rays or particles that pass through the walls of the fused silica separation channel. A similar semiconductor detector for 7-emitting radiopharmaceuticals separated by HPLC was reported by Needham and Delaney (XI). The second detector utilizes a commercially available plastic scintillator material that completely surrounds (360 ) the detection region of the separation channel. Light emitted by the plastic scintillator is collected and focused onto the photocathode of a cooled photomultiplier tube. Alternatively, a third detection scheme utilizes a disk fashioned from commercially available plastic scintillator material positioned between two-room temperature photomultiplier tubes operated in the coincidence counting mode. 

Carbohydrates play an important role in many research and industrial domains. The huge number of stereoisomers, the immense combination possibilities of carbohydrate monomers in oligosaccharides, and the lack of chromophores are the major problems in the analysis of carbohydrates. Capillary electrophoresis (CE), in its various modes of operation, has been developed as a very useful tool in the analysis of carbohydrate species such as monosaccharides and oligosaccharides, glycoproteins, and glycopeptides. 

Several features of capillary electrophoresis are particularly interesting for forensic scientists, namely high separation efficiency, sensitivity, and small amount of samples (nanoliters) and solvents (a few milliliters per day). Regarding different operational modes, all of them are applied, although to a different extent, depending on the type of compounds to be assayed. 

Almost all operational modes of capillary electrophoresis have been combined with mass spectrometry via CF-FAB [68-70], MALDI [57,71], and ESI [72-76]. Of these three technologies, ESI has attained an enviable status as the interface of choice to couple CE with mass spectrometry. A CE/MS interface must address the problem of the low liquid flow rates of the CE process. Other considerations are buffer compositions and electrical contact between the separation buffer and the interface. As with LC/MS systems, only volatile buffers are tolerated in a CE/MS operation. Also, high salt concentrations must be avoided for stable operation of a mass spectrometry system. 

There are several operational modes used in capillary electrophoresis. The main modes are capillary... 

For a given operational mode the separation efficiency N depends on the conditions of electrophoresis such as the type of capillary, background electrolyte, volume and composition of the sample, the applied voltage and temperature. 

Capillary electrophoresis (CE) is a good alternative to GC and LC techniques for profile determination of OL derivatives. CE requires minimal sample preparatiOTi and represents a good compromise between analysis time and satisfactory characterization. The most efficient operative mode to separate phenolic compounds is the borate-based CE, which makes use of a borate run buffer at alkaline pH [52], To date, the most widely used detector in CE is based on UV absorption [53, 54], although the coupling to MS analyzers such as QqQ, IT, TOF has revalorized the potential of this technique [55]. 

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