Liquid chromatography of aromatic amines with photochemical derivatization and tris(bipyridine)ruthenium(III) chemiluminescence detection

[Ru(bpy)2(dcbpy)NHS] labeling/aptamer-based biosensor for the detection of lysozyme by increasing sensitivity with gold nanoparticle amplification

A novel [Ru(bpy)(2)(dcbpy)NHS] labeling/aptamer-based biosensor combined with gold nanoparticle amplification for the determination of lysozyme with an electrochemiluminescence (ECL) method is presented. In this work, an aptamer, an ECL probe, gold nanoparticle amplification, and competition assay are the main protocols employed in ECL detection. With all the protocols used, an original biosensor coupled with an aptamer and [Ru(bpy)(2)(dcbpy)NHS] has been prepared. Its high selectivity and sensitivity are the main advantages over other traditional [Ru(bpy)(3)](2+) biosensors. The electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM) characterization illustrate that this biosensor is fabricated successfully. Finally, the biosensor was applied to a displacement assay in different concentrations of lysozyme solution, and an ultrasensitive ECL signal was obtained. The ECL intensity decreased proportionally to the lysozyme concentration over the range 1.0x10(-13)-1.0x10(-8) mol L(-1) with a detection limit of 1.0x10(-13) mol L(-1). This strategy for the aptasensor opens a rapid, selective, and sensitive route for the detection of lysozyme and potentially other proteins.

Photoinduced chemiluminescence of pharmaceuticals

A screening test for the forward development of chemiluminescence systems able to determine pharmaceutical compounds is reported. The test is based on the on-line photodegradation of the drugs by using a photoreactor consisting of 697 cmx0.5 mm PTFE tubing helically coiled around an 8 W low-pressure mercury lamp. Photodegraded pharmaceuticals are detected by direct chemiluminescence of the resulting photofragments and their subsequent reaction with potassium permanganate in sulphuric acid medium as oxidant. The screening comprised 97 compounds with different molecular structures and relevant members of the most important families of pharmaceuticals are tested (amino acids, carboxylic acids, nitrocompounds, phenyl-alkyl and aromatic amines, sulphonic acid amides, polycarbocyclics, monocyclic N-containing heterocyclics, bicyclic N-containing heterocyclics, tricyclic N-containing heterocyclics, N-S containing heterocyclics...). Due to the relevant influence of the medium for the photodegradation a wide range of pH's and buffer solutions were studied. The proposed strategy (photoinduced chemiluminescence, Ph-CL) allows the development of systems for the determination of many pharmaceuticals which do not present "native" chemiluminescence (e.g. chloramphenicol, dextromethorpham, riboflavin, ephedrine, piperazinamide, chlotrimazole, theophylline...). Moreover, Ph-CL allows to increase the sensitivity of chemiluminescence procedures based on direct chemiluminescence detection (e.g. sulphonamides, thiazides, nicontinamide, nortryptiline, levamisole, phenylbarbituric acid...).

Tris(2,2'-bipyridyl)ruthenium(II) chemiluminescence

This paper critically reviews analytical applications of the chemiluminescence from tris(2,2'-bipyridyl)ruthenium(II) and related compounds published in the open literature between mid-1998 and October 2005. Following the introduction, which summarises the reaction chemistry and reagent generation, the review divides into three major sections that focus on: (i) the techniques that utilise this type of detection chemistry, (ii) the range of analytes that can be determined, and (iii) analogues and derivatives of tris(2,2'-bipyridyl)ruthenium(II).

Use of tris(2,2'-bipyridine)osmium as a photoluminescence-following electron-transfer reagent for postcolumn detection in capillary high-performance liquid chromatography

The photoluminescence-following electron-transfer (PFET) technique, developed in our laboratory, is a sensitive chromatographic detection method for oxidizable analytes. Because the oxidations are homogeneous, the technique avoids the problem of electrode fouling. A liquid-phase oxidant reacts with the electrochemically active analytes after separation, becoming capable of photoluminescence. Laser-induced photoluminescence is measured to quantitate the analytes. Thus, the electrochemical properties of the oxidant determine the detection selectivity, and the spectroscopic properties define the sensitivity. The properties of tris(2,2'-bipyridine)osmium (1) were investigated for use as the liquid-phase oxidant in the PFET system. The redox potential of the complex is less positive than that of tris(2,2'-bipyridine)ruthenium (2); thus, on-line generation of 1(3+) by reaction with PbO2, and selective oxidation of catechols by 1(3+), was possible. The mild oxidizing power of 1(3+) led to a lower background signal (compared to 2(3+)) when mixed with acidic mobile phases. Photoluminescence from 1(2+) was much weaker than that from 2(2+); nonetheless, the system achieved subnanomolar detection limits for dopamine, 3-methoxytyramine, and serotonin. Dopamine and 3-methoxytyramine in rat brain striatal dialysates were determined before and after the injection of nomifensine. The pH of the mobile phase can govern the detection selectivity, since oxidation of most organics is accompanied by proton transfer. Reaction of 1 with catechols showed pH-dependent sensitivity resulting from pH-dependent reaction rate changes. Since the reaction rate is also temperature dependent, increased temperature at the mixer resulted in higher sensitivity. However, the noise level also increased at elevated temperature; thus, the detection limit did not improve.

High-performance liquid chromatography of aromatic compounds with photochemical decomposition and tris(2,2′-bipyridine)ruthenium(III) chemiluminescence detection

A novel high-performance liquid chromatographic method for the determination of aromatic compounds based on the on-line photochemical degradation and subsequent tris(2,2'-bipyridine)ruthenium(III) chemiluminescence detection has been developed. Chemiluminescence intensity depended upon the number of aromatic rings, UV irradiation time, and variety of substituted functional groups. One of the decomposition products of aromatic compounds by UV irradiation was identified as oxalic acid. As one application of this methodology, determination of catechins in tea has been shown. Calibration graphs, based on standard (-)-epicatechin and (-)-epigallocatechin gallate solutions, were linear over the range of 0.1-50 microM. The detection limits (signal-to-noise ratio=3) were 0.8 pmol for (-)-epigallocatechin gallate and 1.2 pmol for (-)-epicatechin. The high-performance liquid chromatography-chemiluminescence (HPLC-CL) detection method with a post-column photochemical reactor can be applied to the sensitive and selective determination of catechins in tea.

Enantiomeric separation of naphthalene-2,3-dicarboxaldehyde derivatized dl-3,4-dihydroxyphenylalanine and optical purity analysis of l-3,4-dihydroxyphenylalanine drug by cyclodextrin-modified micellar electrokinetic chromatography

A new cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC) method for the enantiomeric separation of 3,4-dihydroxyphenylalanine (DOPA), derivatized with naphthalene-2,3-dicarboxaldehyde (NDA) to produce cyanobenzoisoindole (CBI) derivative, has been developed. The unsubstituted alpha-, beta-, gamma-cyclodextrins (CDs) and hydroxypropyl-substituted alpha-, beta-, gamma-CDs, as chiral selector, were examined for the enantiomeric separation of CBI-DL-DOPA. In addition to the concentration of chiral selector, some other experimental factors also have been optimized, such as concentration of borate buffer, content of sodium dodecyl sulphate (SDS), pH of electrolyte and applied voltage. Optimal separation was obtained at pH 8.0, 100 mM borate solution containing 5 mM HP-gamma-CD and 120 mM SDS, as well as 18 kV applied voltage and 25 degrees C capillary temperature. Detection was followed by direct UV absorptiometric measurements at 254 nm. The developed method was employed for optical purity analysis of levodopa drug and allowed the determination of 0.14% D-DOPA in L-3,4-dihydroxyphenylalanine (levodopa) with well peak identification.

Determination of aromatic and branched-chain amino acids in plasma by HPLC with electrogenerated Ru(bpy)3(3+) chemiluminescence detection

An HPLC method is described for the electrochemiluminescence (ECL) detection of amino acids, following cycloaddition reaction of their amino groups with divinyl sulfone (DVS), using electrogenerated tris(bipyridine)ruthenium(III). The derivatization reaction conditions were examined, with the optimum conditions found to be 40 mM DVS (pH 8.0) at 50 degrees C for 15 min. Detection limits for the 15 amino acids examined varied greatly (0.04-8.0 pmol) using a standard solution by flow injection analysis (FIA). These optimized conditions were used for HPLC determination of the amino acids in human plasma. A linear relationship was obtained up to 100 pmol on a column for aromatic and branched-chain amino acids. Recoveries of Tyr, Met, Val, Leu, Ile, Phe and Trp when added to human plasma (1 micromol/10 ml plasma, n=5) were 101.5+/-1.1, 99.0+/-1.2, 98.0+/-1.4, 101.1+/-1.6, 95.1+/-1.6, 99.2+/-1.5 and 97.7+/-1.3 % (mean+/-S.D.) respectively. The concentrations of the amino acids in the plasma are in good agreement with other published data.

Chemiluminescence detection in HPLC and CE for pharmaceutical and biomedical analysis

The present paper reviews the developments and applications of chemiluminescence detection with HPLC and CE in pharmaceutical and biomedical analysis. The chemiluminescence systems, chemiluminogenic reagents and derivatization reagents, improvements in instrumental design as well as their contributions to the practical applications, are all presented. The advantages and limitations of current detection methodology and future prospects for improvement are briefly discussed.

Stille-type cross-coupling-An efficient way to various symmetrically and unsymmetrically substituted methyl-bipyridines: toward new ATRP catalysts

Various mono- and disubstituted 2,2'-bipyridines were synthesized in high yields and multigram scales utilizing Stille-type coupling procedures. The corresponding bromo-picoline and tributyltin-picoline building blocks were prepared from commercially available amino-picoline compounds. As first examples of metal complexes, 4,5'-dimethyl-2,2'-bipyridine was reacted with copper(II) and iron(II) ions and investigated as catalyst in ATRP.