High performance capillary electrophoresis detectors

A computer program was compiled to work out the ray-tracing of UV detector of high performance capillary electrophoresis at the investigation of 5 and 6 (98MI59). The capacity factor of 5 at different temperature and at different mobile phase compositions was experimentally determined in bonded-phase chromatography with ion suppression (98MI15). 

Organolead and organoselenium compounds were separated satisfactorily by high-performance capillary electrophoresis, using /1-cyclodextrin-modified micellar electroki-netic chromatography with on-column UVV detector set at 210 nm130. 

One variant of absorbance detection that is widely used in HPLC can also be used in high performance capillary electrophoresis. For compounds that exhibit a very weak UV absorption, buffers such as chromate or phthalate, which have high absorption properties, can be used. Under these experimental conditions, the UV absorbance diminishes as analytes flow past the detector (due to the dilution effect of the electrolyte). This leads to negative peaks on the recorder (see Fig. 8.9). 

Abbreviations DAD, diode array detector FIC, flow injection chromatography FIA-SPE-MEKC, flow injection analysis-solid phase extraction-micellar electro kinetic chromatography HPLC-FI-CH, high performance liquid chromatography-flow injection-chemiluminescence FI-CH, flow injection-chemiluminescence detection FIPCE, high performance capillary electrophoresis LOD, limit of detection LOQ, limit of quantitation SIC, sequential injection chromatography. 

To perform capillary electrophoresis the following basic components are necessary a high voltage power source, a detector and a buffer filled capillary (see Fig. 1). 

CZE = capillary zone electrophoresis EC = electrochemical detector GC = gas chromatography HCD = Hall conductivity detector HPLC = high performance liquid chromatography IDMS = isotope dilution mass spectrometry MS = mass spectrometry RSD = relative standard deviation SEE = supercritical fluid extraction SPE = solid phase extraction UV = ultraviolet absorbance detection... 

The method of complete electrolysis is also important in elucidating the mechanism of an electrode reaction. Usually, the substance under study is completely electrolyzed at a controlled potential and the products are identified and determined by appropriate methods, such as gas chromatography (GC), high-performance liquid chromatography (HPLC), and capillary electrophoresis. In the GC method, the products are often identified and determined by the standard addition method. If the standard addition method is not applicable, however, other identification/determination techniques such as GC-MS should be used. The HPLC method is convenient when the product is thermally unstable or difficult to vaporize. HPLC instruments equipped with a high-sensitivity UV detector are the most popular, but a more sophisticated system like LC-MS may also be employed. In some cases, the products are separated from the solvent-supporting electrolyte system by such processes as vaporization, extraction and precipitation. If the products need to be collected separately, a preparative chromatographic method is use-... 

Notes LOD, limit of detection MeOH, methanol EtOH, ethanol ACN, acetonitrile EtAC, ethyl acetate SPE, solid phase extraction HLB (hydrophilic lipophilic balanced) TFA, trifluoroacetic acid GC, gas chromatography TMS, trimethylsilyl MS, mass spectrometry HPLC, high-performance liquid chromatography DAD, diode array detector NMR, nuclear magnetic resonance ESI, electrospray ionization APCI, atmospheric pressure chemical ionization CE, capillary electrophoresis ECD, electrochemical detector CD, conductivity detector TLC, thin layer chromatography PDA, photodiode array detector. 

There are few methods which can measure well-defined metal fractions with sufficient sensitivity for direct use with environmental samples (approach B in Fig. 8.2). Nevertheless, this approach is necessary in the experimental determination of the distribution of compounds that are labile with respect to the time scales of the analytical method. Recent literature indicates that high-performance liquid (HPLC) and gas chromatographic (GC) based techniques may have such capabilities (Batley and Low, 1989 Chau and Wong, 1989 van Loon and Barefoot, 1992 Kitazume et al, 1993 Rottmann and Heumann, 1994 Baxter and Freeh, 1995 Szpunar-Lobinska et al, 1995 Ellis and Roberts, 1997 Vogl and Heumann, 1998). The ability to vary both the stationary and mobile phases, in conjunction with suitable detector selection (e.g. ICP-MS), provides considerable discriminatory power. HPLC is the superior method GC has the disadvantage that species normally need to be derivatised to volatile forms prior to analysis. Capillary electrophoresis also shows promise as a metal speciation tool its main advantage is the absence of potential equilibria perturbation, interactions... 

A capillary electrophoresis system is comparatively simple. The basic components (Fig. 6.1) include the power supply which provides the high voltage necessary for the separation, the capillary in which the separation takes place, the detector which determines the sensitivity of the separation, and the data acquisition system which records the electropherogram. Some instruments also perform fraction collection. The final electropherogram looks similar to a chromatogram obtained from HPLC. 

Early in the development of capillary electrophoresis, it was noted that the successful detection of separated sample components present within the narrow confines of these capillary tubes posed a major challenge (2)- In response to this challenge, much research has been directed toward the development of sensitive and selective detectors for capillary electrophoresis. CE detector technology has been largely borrowed from the field of high-performance liquid chromatography (HPLC), especially from micro-column HPLC. 

Three simple, on-line radioisotope detectors for capillary electrophoresis were described and characterized for the analysis of 43P-labeled analytes. The minimum limit of detection for these systems was shown to be strongly dependent upon the conditions under which the analysis is performed. For standard CE separations performed at a relatively high (constant) voltage, the minimum limit of detection was found to be in the low nanocurie (injected sample... 

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