HPCE

Table 2 Additives Frequently Used in HPCE for Electro-osmotic Flow (EOF) Modification...

Sample adsorption to the silica wall is a problem in HPCE, one that is highly undesirable. As we mentioned earlier, adsorption can be minimized by proper buffer selection, additives, or chemical modification of the surface. The selection of pH is one of the simplest separation parameters to manipulate and is critical to the success of all electrophoretic separations. The pH of the media will determine the charge of the sample and the charge of the silica surface. At low values of pH, the capillary wall is protonated, the EOF... 

The detection of the migrating sample boundary in CE can be accomplished by UV, fluorescent, electrochemical, radiochemical, conductivity, and mass spectrometry (MS) means. The use of high-sensitivity detection systems is always a key issue in CE applications. The sensitivity of HPCE detectors may be at least 2 to 3 orders of magnitude better than that of HPLC detectors. Since the detection cell volume is very small, the concentration sensitivity... 

The initial driving force behind the development of HPCE came from the need of better and faster separations for biologically important molecules used in biotechnology research and in the biopharmaceutical industry. Traditional electrophoresis is an established method in life sciences however,... 

HPCE separations utilizing the MEKC mode allow the electrophoretic separations of neutral components using detergent micelles. The advantage of using detergents is that in most cases the sample cleanup and solubilization step can be eliminated because of the presence of the detergent. Penicillins,112113... 

The major problem with proteins in HPCE is their tendency to adsorb to the silica surface. This can be minimized or prevented by modifying the... 

Ulfelder, K., Anderson, K., and Schwartz, H. E., Analysis of PCR products and DNA restriction fragments to detect AIDS (HIV-1) virus in blood, poster presentation, HPCE 91, San Diego, CA, 1991. 

Because HPLC and HPCE are based on different physico-chemical principles, HPCE may be expected to address areas in which HPLC has shortcomings [884]. One such area is time of separation. In terms of speed of analysis, selectivity, quantitation, methods to control separation mechanism, orthogonality, CE performs better than conventional electrophoresis and varies from HPLC (Table 4.49). CE has very high efficiency compared to HPLC (up to two orders of magnitude) or GC. For typical capillary dimensions 105—106 theoretical plates are common in CE compared to 20 000 for a conventional HPLC column and... 

HPCE High-performance capillary (2) Interaction chromatography... 

A high performance capillary electrophoresis (HPCE) was described for the separation and simultaneous determination of OTC, TC, CTC, DC, and chloramphenicol in honey. The use of buffer pH 3.2 containing 0.02 mol/L Na2HP04 and 0.01 mol/L citric acid with addition of 4% (v/v) A-methylmorpholine and 12% (v/v) acetonitrile demonstrated a good separation of these five antibiotics within 20 min. The proposed method gave detection limit (signal to noise ratio > 5) of 20 pg/L for OTC [26],... 

Figure 1 Schematic diagram of an HPCE apparatus, (a) Main part (b) holder for FL detector (c) CL detector. (From Ref. 69, with permission.)...

A schematic diagram of an HPCE system is shown in Figure 4.54. The fused-quartz capillary is generally 50-75 cm long with an i.d. of 25-100 gm... 

Different separation mechanisms, which determine selectivity, can be exploited in HPCE by appropriate choice of operating conditions. There are four principal modes of operation (Table 4.22) and it should be noted that in only one, micellar electrokinetic capillary chromatography (MEKC), is it possible to separate neutral species from one another. 

Figure 4.59 illustrates some typical separations employing different modes of HPCE. 

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