Ce detection

Fang JL, Vaca CE. Detection of DNA adducts of acetaldehye in peripheral white blood cells of alcohol abusers. Carcinogenesis 1997 18 627-632. 

CE detection is similar to detectors in, and include absorbance, fluorescence, electrochemical, and mass spectrometric detectors. The capillary can also be filled with a gel, which eliminates the electroosmotic flow. Separation is accomplished as in conventional gel electrophoresis but the capillary allows higher resolution, greater sensitivity, and on-line detection. In CE, low picogram amounts of analytes can be detected using glass fiber optics. However, this does not mean low limits of detection since only a few nanoliters can be injected. 

In CE detection is performed on-column, so the detection cell is defined by the diameter of the capillary. Because sensitivity is proportional to the path length, sensitivity of absorbance methods is limited. Thus, capillary... 

Two developmental difficulties existed in the application of electrochemical methods to CE detection. The first involved the cross-talk or interference that resulted from the high voltages used in CE separations. These dc voltages may be as high as 50 kV, and the resulting electroosmotic currents can be up to six orders of magnitude greater than the faradaic currents measured at an amperometric detector poised... 

Lasers are another source of excitation radiation used in fluorescence detection systems. The high-directional output of a laser maximizes the fraction of total output that can be easily focused down to a spot size compatible with the dimensions of CE detection cells. The output of a laser is also typically monochromatic, or a discrete set of spectrally narrow lines. This type of output makes it relatively easy to filter out low-level incoherent plasma radiation and undesired emission lines without greatly diminishing the overall output power. In addition, many lasers provide flexibility in terms of pulse width and repetition rate, which allows one to optimize excitation with respect to analyte photostability. 

CL detection can be used to probe intrinsic luminescence, such as that found in numerous biological systems (bioluminescence), or analytes of interest can be derivatized by reaction with an isothiocyanate or succinimidyl ester-linked chemiluminescent moiety. The first reported use of CL for CE detection was by Kara et who used peroxyoxolate as the luminophore to detect a... 

The UV absorbance detector is one of the most widely used systems in CE. Detection takes place in the same separation capillary, avoiding band broadening of the separated compounds. Since the internal diameter of the capillary is very small (25-100 (xm), the detection pathlength is very short and the concentration sensitivity is typically 10-20 times poorer than that obtained with the same type of detector in other separation techniques (e.g., HPLC). 

Several techniques have been developed for CE detection, such as indirect and direct ultravi-olet/visible (UVA is) optical methods. Laser-induced fluorescence OLIF) is widely used. Direct photometric detection based on UVA is light absorbance accounts for over half of all CE application. Absorbance detection operates at wavelength ranging from 190 to 800 nm. It covers both ultraviolet and visible regions. The usually used wavelengths for detection are 190 and 200 nm for... 

UV-visible spectrophotometry is still important for LC and CE detection of numerous important naturally occurring groups of substances, such as flavonoids, phenolic acids, anthraquinones, and cou-marins, because they have very characteristic UV spectra. 

Laser-induced fluorescence is the standard CE detection method in DNA sequencing, due to its high sensitivity... 

In a high percentage of HPLC and CE separations, monitoring is performed with ultraviolet detectors. However, many immunoassays are aimed at the determination of analytes that are present at concentrations below the UV detection limit. Furthermore, as indicated before, desorption buffers can decrease the sensitivity of immunochromatographic assays. Approaches used to enhance sensitivity in conventional immunoassay formats do the same in immuno-HPLC and immuno-CE detection and for this reason are considered together under this subheading. 

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