A.C. Calokerinos

Chemiluminescence-based detection: principles and analytical applications in flowing streams and in immunoassays

The present paper provides the principles of chemiluminescence (CL) and its powerful applications in analytical chemistry, mainly in the area of flow injection analysis, column liquid chromatographic and capillary electrophoretic separating systems, and its potential in immunoassays. CL is light produced by a chemical reaction. The most common advantages of chemiluminescent reactions are the relatively simple instrumentation required, the very low detection limits and wide dynamic ranges, which have contributed to the interest of CL detection in flow injection analysis, high performance liquid chromatography, including miniaturized systems, and, most recently, the exploding area of capillary electrophoresis. The latter powerful microanalytical separation technique offers high numbers of theoretical plates and relatively short analysis times requiring only small sample volumes, the migrating system comprising aqueous buffer solutions. In non-isotopic immunoassays, covering a great variety of applications in human and veterinary medicine, forensic medicine, agriculture and food industry, the radioisotope is replaced by a fluorescence or chemiluminescent label. The use of CL as a detection principle permits quantitative determination of various compounds at low concentrations. Disadvantages of the CL-based technique may include lack of sufficient selectivity and sensitivity to various physicochemical factors.

Chemiluminescence determination of some local anaesthetics

Abstract The analytical possibilities of the Chemiluminescence observed from some local anaesthetics on acidic permanganate treatment are investigated. Five drugs belonging to the p-aminobenzoate series gave significant emission and the reagent concentrations for their determination were optimized. The following detection limits were obtained: benzocaine, 30 ng ml−1; butacaine, 20 ng ml−1; butoform, 30 ng ml−1; procaine, 40 ng ml−1 and tetracaine 3 ng ml−1. The application of the reaction to the analysis of some pharmaceutical preparations containing benzocaine and procaine was evaluated.

Chemiluminescence determination of tetracyclines based on their reaction with hydrogen peroxide catalysed by the copper ion

A flow injection-based method for the determination of tetracycline, chlortetracycline and oxytetracycline has been proposed. It is based on the reaction of the tetracyclines with hydrogen peroxide, catalysed by the copper ion in ammonia medium. Persulfate was used as a co-oxidizing agent. The procedure allows the determination of 0.025–2.5 nmol of chlortetracycline and 0.25–25 nmol of tetracycline and oxytetracycline (50 µl per injection) by the flow-injection method compared with 0.005–50 µmol l–1 of chlortetracycline and 0.05–500 µmol l–1 of tetracycline and oxytetracycline by the classical batch method. The method is sensitive, selective and easy to operate and can be used for the determination of tetracyclines in pharmaceutical preparations. A discussion on the possible reaction mechanism is presented.

Detection in the liquid phase applying chemiluminescence

Several chemiluminescence-based reactions are applicable to the determination of various bio-pharmaceutically important analytes, and they can be applied for monitoring chemiluminescence emission using flow injection, liquid chromatographic and capillary electrophoretic analysis, as well as for the development of chemiluminescence-based sensors or in immunoassays. As in general the emission intensity is linearly proportional to the concentration of any of the reagents, the technique allows the analysis of different species involved in the light-producing reaction, amongst which are the chemiluminescent reagent, oxidants, inhibitors, cofactors, catalysts, some fluorophore, etc. The present overview illustrates some important applications of the last decade on this rather unfamiliar luminescence technique to detectional challenges in the liquid phase. The required instrumentation is limited as no external light source is needed. Also, the technique opens perspectives for increasing detection sensitivity in miniaturized flowing streams. On the other hand, several drawbacks still limit full application, eg dependence of the emission signal upon a number of environmental factors forcing the analyst to make a compromise between separating and measuring conditions, a lack of selectivity in specific cases, the critical detection of the signal at strictly defined periods, especially in the case of sharp emission vs time profiles, and the development of detection devices in capillary electrophoresis.

Chemiluminescence Determination of Tiopronin by Flow Injection Analysis Based on Cerium(IV) Oxidation Sensitized by Quinine

A flow injection analysis method is proposed for the determination of tiopronin based upon the oxidation by cerium(IV) in dilute sulfuric acid medium and sensitized by quinine. With the peak height as a quantitative parameter applying optimum working conditions, tiopronin is determined over the 1-400 microM range (150 microliters per injection, n = 10, r = 0.9994) with a detection limit of 0.34 microM and an RSD (n = 10) less than 2% at 20 and 50 microM. The proposed method, combining the advantages of speed and sensitivity, was applied to the routine determination of tiopronin in a pharmaceutical preparation.

Chemiluminescence analysis of captopril : comparison between luminol and rhodamine B-sensitized cerium(IV) methods

Two chemiluminescence methods for the determination of captopril are compared in the present paper. The first method is based on the reaction of captopril with the luminol-hydrogen peroxide-copper(II) system, the copper(II) ion acting as a key species in the light-emitting process. The catalytic activity of copper(II) decreases due to complex formation with the sulphhydrylic captopril analyte. Application of this indirect method allows captopril determinations in the 8.0-1.0 microM range as starting concentrations. Similarly, captopril was capable of generating chemiluminescence from acid cerium(IV) solutions, a reaction that could be analytically exploited by the inclusion of the rhodamine B fluorophore yielding a sensitized-type of chemiluminescence emission that allowed quantitation of captopril concentrations in the 0.1-6.0 microM range with a detection limit of 0.037 microM (original concentration). For both types of reaction the experimental conditions were optimized and a direct application was carried out on a commercial drug formulation.

Flow-injection chemiluminometric determination of steroids

Abstract A rapid, accurate, precise and fully automated flow-injection method is described for the determination of 0.02–0.50 μg ml −1 cortisone, 0.02–1.00 μg ml −1 hydrocortisone and 0.20–5.00 μg ml −1 dexamethasone in aqueous solutions and of 1.0–20.0 μg ml −1 prednisolone, methylprednisolone, progesterone, corticosterone and testosterone and 2.0–20.0 μg ml −1 betamethasone in 20% (v/v) acetonitrile solutions. The methods is based on the sensitizing effect of each steroid on the chemiluminogenic cerium(IV)sulphite reaction. Limits of detection are in the ranges 0.013–0.019 and 0.05–4.00 μg ml −1 for aqueous and acetonitrile solutions, respectively. Common excipients do not interfere greatly and the mean recovery of steroids from commercial formulations was 102.6% (range 94.2–109.0%). The method allows the measurement of up to 100 samples per hour and can be used for content uniformity tests and the results were in good agreement with the official method for commercial formulations with a relative error

Chemiluminescence determination of tiopronin and its metabolite 2-mercaptopropionic acid in human urine by HPLC coupled with flow injection

SummaryIn previous pharmacokinetic studies tiopronin, a drug used for effective treatment of cystinuria and rheumatoid arthritis, and its metabolite 2-mercaptopropionic acid were analysed by conventional liquid chromatography with pre- and post-column derivatization and UV detection. Now a novel HPLC-coupled chemiluminescence-flow-injection analysis (CL-FIA) method has been developed for the determination of tiopronin and 2-mercaptopropionic acid in urine. The method is based on chemiluminescence from a Ce(IV) oxidation system sensitized by quinine, as proposed earlier by this group, and flow-injection analysis. The method, which has the advantages of high sensitivity and selectivity, simple sample treatment and prompt production of results, has also been preliminarily adapted for pharmacokinetic study of tiopronin in urine.

Continuous-flow molecular emission cavity analysis for sulphide

Abstract Sulphide (1–10 μg ml −1 ) is determined by mixing the sample with an excess of orthophosphoric acid in a segmented continuous-flow system. The hydrogen sulphide evolved is swept into the cavity for generation of S 2 emission. The analysis is completely automated, requires no sample pretreatment and samples can be analyzed at 24 h −1 .

Indirect potentiometric determination of sulphide with a cadmium ion-selective electrode

An indirect potentiometric method is described for the determination of sulphide in the range 0.3–300 μg (0.06–60 μg ml−1). A known excess of cadmium(II) is added to the sample and the unreacted cadmium ion is titrated with EDTA using a solid-state cadmium ion-selective electrode. The method is applied successfully for determinations of sulphide in spiked air samples and of sulphur in steels.