Derivatization of biomolecules for chemiluminescent detection in capillary electrophoresis

An overview is presented on the power and drawbacks of the relatively unfamiliar chemiluminescence-based detection technique applied in analysis by capillary electrophoresis, for determining chemically derivatized biomolecules. Examples of the most common systems are given for many series of biologically active compounds as well as for some pharmaceuticals. The most common chemiluminescent systems include the application of peroxyoxalate ester chemiluminescence, acridinium esters, luminol and derivatives, detection based on the tris(2,2'-bipyridine)ruthenium(III) system, the huge potentials offered by direct oxidations-though often with still unelucidated reaction mechanisms-and the powerful area of bioluminescence techniques, revealing as well the fast developing area of microchip-based analysis employing this specific luminescence principle.

Determination of Sulpiride by Capillary Electrophoresis with End-Column Electrogenerated Chemiluminescence Detection

Background: Capillary electrophoresis (CE) with tris(2,2′-bipyridyl)ruthenium(II) [Ru(bpy)32+]-electrogenerated chemiluminescence (ECL) detection is a promising method for clinical analysis. In this study, a method combining CE with Ru(bpy)32+ ECL (CE-ECL) detection that can be applied to amine-containing clinical species was developed, and the performance of CE-ECL as a quantitative method for determination of sulpiride in human plasma or urine was evaluated.

Methods: Sulpiride was separated by capillary zone electrophoresis in uncoated fused-silica capillaries [50 cm × 25 μm (i.d.)] filled with phosphate buffer (pH 8.0) and a driving voltage of +15 kV, with end-column Ru(bpy)32+ ECL detection. A platinum disc electrode was used as working electrode. Sulpiride in human plasma or urine samples (100 μL) was extracted by a double-step liquid-liquid extraction procedure, dried under nitrogen at 35 °C in a water bath, and reconstituted with 100 μL of filtered water. The extraction solvent was ethyl acetate–dichloromethane (5:1 by volume).

Results: Under optimum conditions (pH 8.0 phosphate buffer, injection for 6 s at 10 kV, and +1.2 V as detection potential), separation of sulpiride was accomplished within 4 min. The calibration curve was linear over a concentration range of 0.05–25.0 μmol/L, and the limit of detection was 2.9 × 10−8 mol/L for sulpiride. Intra- and interday CVs for ECL intensities were <6%. Extraction recoveries of sulpiride were 95.6–101% with CVs of 2.9–6.0%. The method was clinically validated for patient plasma and urine samples.

Conclusions: CE combined with Ru(bpy)32+ ECL is reproducible, precise, selective, and enables the analysis of sulpiride in human plasma and urine. It thus is of value for rapid and efficient analysis of amine-containing analytes of clinical interest.

Ultrasensitive chemiluminescence detection in capillary electrophoresis

Capillary electrophoresis techniques offer high plate numbers and are highly suited for the efficient separations of a wide variety of chemical components in diverse matrices. Because of the small capillary and detection cell dimensions, together with the minute volumes of samples to be injected, sensitive detection schemes based on different physicochemical principles are being developed. One logical approach to increased sensitivity in capillary electrophoresis detection has been the development of chemiluminescence-based detectors. The development of on-line ultrasensitive chemiluminescence detection (referred to the concentration detection limit of nM order of magnitude or mass detection limit of amol order of magnitude) in capillary electrophoresis system is reviewed. The applications and limitations of the current detection methodology are briefly considered and future prospects for the development are discussed.

Ultrasensitive chemiluminescence detection of sub-fM level Co(II) in capillary electrophoresis

A method of on-line ultrasensitive chemiluminescence detection with capillary electrophoresis for Co(II) is reported. Using our newly developed capillary electrophoresis with chemiluminescence detection system and novel mixing mode of the reagents, the effects of field-amplified injection on detection limits of metal ions were studied in detail. The sub-fM level (1.3 x 10(-16) M, 1.6 x 10(-24) mol, 1 molecule) detection of cobalt ions in ultradilute solution was performed. The catalytic behavior of the chemiluminescence reaction of luminol and hydrogen peroxide by cobalt ions and the reaction conditions, such as the concentration of luminol, H2O2, and pH of chemiluminescence reagent were investigated. The separation of fM level Co(II) and trace amounts of Ni(II) was performed successfully.

Capillary electrophoresis of monoamines and catechol with indirect chemiluminescence detection

A capillary electrophoresis (CE)/indirect chemiluminescence (CL) detection method is described for monoamines, viz., serotonin (5-HT), dopamine (DA), epinephrine (EP), and norepinephrine (NE) and for catechol (CA). Optimal separation and detection were obtained with an electrophoretic buffer of 10 mM sodium borate (pH 9.5) containing 5 mM luminol and 25 mM H2O2, and a catalyst solution of 30 microM CuSO4 in 30 mM borate buffer (pH 10.0). Complete separation of 5-HT, DA, EP, NE and CA was achieved in less than 5 min. The Cu(II)-catalyzed luminol CL reaction was employed to provide the high and constant background. Since monoamines and catechol can form stable complexes with Cu(II), inverted analyte peaks due to decreased catalytic activity of Cu(II) can be detected. The degree of CL suppression is proportional to the analyte concentrations. Linearity (r> or =20.99) over two orders of magnitude was generally obtained. The concentration limits of detection (CLODs) for the monoamines and catechol studied were between 0.5 and 3.1 uM. The relative standard deviation (RSD) values on peak size and migration time were in the ranges 3.2-4.4% and 0.4-0.5%, respectively. The applicability of the method for the analysis of pharmaceutical and biological samples was examined.

Post-column derivatization for fluorescence and chemiluminescence detection in capillary electrophoresis

Instrumental developments and applications of post-column derivatization for fluorescence and chemiluminescence detection in capillary electrophoresis (CE) are reviewed. Various systems to merge the reagent solution with the separation medium have been developed, including coaxial capillary reactors, gap reactors and free solution or end-column systems. For all reactor types the geometry of the system, as well as the method to propel the reaction mixture (by pressure or by voltage) appeared to be critical to preserve the separation efficiency. Plate numbers of over 100,000 could be realised with different reactors. The strict requirements on the rate of post-column derivatization reactions to be applied in CE limit the number of different reagents that have been used. For fluorescence detection, with laser or lamps as the excitation source, so far mainly o-phthalaldehyde and its naphthalene analogue have been used as reagent. Derivatization systems that are based on complexation reactions also showed good promise for application in CE. Detection limits could be obtained that were comparable to those obtained after pre-column derivatization. Various reagents for chemiluminescence detection (e.g. the luminol and peroxyoxalate systems) have been studied. The often complicated chemistry involved made application of these reagents in CE even more difficult. Results obtained so far, in terms of sensitivity, have not been up to expectation, with detection limits usually in the order of micromol l(-1).

Labeling reactions applicable to chromatography and electrophoresis of minute amounts of proteins

Chromatography and electrophoresis have become extremely valuable and important methods for the separation, purification, detection and analysis of biopolymers and HPLC/HPCE may become the premier, preferable approaches for both qualitative and quantitative analyses of most proteins, especially from recombinant materials. This includes smaller peptides, polypeptides, proteins, antibodies and all types of protein or antibody-conjugates (antibody-enzyme, protein-fluorescent probe, antibody-drug and so forth). This entire Topical Issue of Journal of Chromatography emphasizes the application of chromatography and electrophoresis to protein analysis. This particular review deals with approaches to the selective tagging or labeling of proteins at trace (minute) levels, again using either chromatography or electrophoresis, with the emphasis on modern HPLC/HPCE methods and approaches. We discuss here both pre- and post-column labeling methods and reagents, techniques for realizing selective labeling of proteins or antibodies, applicable approaches to protein preconcentration in both HPLC and HPCE areas and in general, methods for improving (lowering) detection limits for proteins utilizing chemical or physical derivatization and/or preconcentration techniques. There are really two major goals or emphases in that which follows: (1) methods for selective labeling of proteins prior to or after HPLC/HPCE and (2) labeling of proteins at trace levels for improved separation-detection and lowered detection limits. We discuss here a large number of specific references related to both pre- and post-column/capillary derivatizations for proteins, as well as methods for improved detectability in both HPLC and HPCE by, for example, analyte preconcentration on a solid-phase extractor or membrane support, capillary isotachophoresis and other methods. Selective reactions or derivatizations on proteins refers to the ability to tag the protein at specific (e.g. reactive amino sites) in a controlled manner, with the products having the same number of tags all at the very same site or sites. The products are all the same species, having the same number of tags at the same locations on the protein. Selective reactions can also refer to the idea of tagging all of the protein sample at only a single, same site or at all available sites, homogeneously.