Capillary electrophoresis ultraviolet detection technique

Fig. 5.4.12a-d Electropherograms of pure standards containing nine BA conjugates at a concentration of 50 nmol/ml (a), a blank serum sample from a healthy subject (b), the same serum sample spiked with 50 nmol/ml of nine different BAs (c) and serum sample from a patient with chronic hepatitis infection (d) analyzed by the capillary electrophoresis technique. Ultraviolet absorbance detection at 195 nm (reprinted from [30])... 

High-pressure liquid chromatography (HPLC) with fluorescence detection, ion-trap mass spectrometry (ITMS), and capillary electrophoresis (CE) with ultraviolet detection, three novel detection techniques for the analysis of cocaine in hair, have been evaluated by Tagliaro et aU°- and Traldi et al. The HPLC technique was highly sensitive, capable of detecting 0.015 ng/mg of cocaine in hair. The CE method was sensitive and highly selective. ITMS analysis of hair readily demonstrated the presence of cocaine in hair, but cocaine metabolites were more difficult to identify. 

The first exposure to spectroscopy for most scientists is ultraviolet/ visible absorbance. As virtually every HPLC chromatograph employed in the pharmaceutical industry uses UV absorbance as the detection method, it is no wonder that the most popular hyphenated technique is HPLC-DAD. DAD spectrographs have been coupled to all liquid-based chromatographic systems including HPLC (preparative, analytical, and microbore), capillary electrophoresis (CE) and supercritical fluid chromatography (SFC). There have been several successes with TLC plates,18 but it is more common for developed plates to be scraped and the sample analyzed offline. 

A number of less commonly used analytical techniques are available for determining PAHs. These include synchronous luminescence spectroscopy (SLS), resonant (R)/nonresonant (NR)-synchronous scan luminescence (SSL) spectrometry, room temperature phosphorescence (RTP), ultraviolet-resonance Raman spectroscopy (UV-RRS), x-ray excited optical luminescence spectroscopy (XEOL), laser-induced molecular fluorescence (LIMP), supersonic jet/laser induced fluorescence (SSJ/LIF), low- temperature fluorescence spectroscopy (LTFS), high-resolution low-temperature spectrofluorometry, low-temperature molecular luminescence spectrometry (LT-MLS), and supersonic jet spectroscopy/capillary supercritical fluid chromatography (SJS/SFC) Asher 1984 Garrigues and Ewald 1987 Goates et al. 1989 Jones et al. 1988 Lai et al. 1990 Lamotte et al. 1985 Lin et al. 1991 Popl et al. 1975 Richardson and Ando 1977 Saber et al. 1991 Vo-Dinh et al. 1984 Vo- Dinh and Abbott 1984 Vo-Dinh 1981 Woo et al. 1980). More recent methods for the determination of PAHs in environmental samples include GC-MS with stable isotope dilution calibration (Bushby et al. 1993), capillary electrophoresis with UV-laser excited fluorescence detection (Nie et al. 1993), and laser desorption laser photoionization time-of-flight mass spectrometry of direct determination of PAH in solid waste matrices (Dale et al. 1993). 

Capillary electrophoresis is an excellent microseparation technique that has been used for the separation of a wide diversity of different molecules." Its separation capabilities extend to ions, small molecules (such as amino acids), and large biomolecules (such as peptides, proteins, and nucleic acids). Indeed the human genome project owes its success, in part, to the use of CE for the separation of DNA bases. In the past, CE has been combined with detection devices such as ultraviolet (UV) and laser-induced fluorescence (LIE) spectrophotometers. The detection of the separated analytes is carried out on column by etching the capillary. Unfortunately, UV detection lacks sensitivity and not every compound of interest will absorb in the UV region of the spectmm. Detection using LIE is sensitive, however, the analytes of interest may require derivatization with a fluorescent tag or have an aromatic amino acid in their structure (e.g., proteins and peptides). An advantage of MS detection that neither UV nor LIE detection provides is the information necessary to directly determine the structure of the detected analyte(s). 

For more complex samples with a number of electroactive species to be determined, separation by HPLC, or other methods such as ion chromatography or capillary electrophoresis, followed by coulometric detection is better suited. Its applications in HPLC are usually to oxidizable organic species that cannot be determined by ultraviolet absorption, the standard detection technique in HPLC. Examples for such species include amines and phenols, catecholamines (such as the neurotransmitters adrenaline and... 

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