A Graphite-Polyurethane Composite Electrode for the Analysis of Furosemide

A graphite-polyurethane composite electrode has been used for the determination of furosemide, a antihypertensive drug, in pharmaceutical samples by anodic oxidation. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the electrooxidation process at +1.0 V vs. SCE over a wide pH range, with the result that no adsorption of analyte or products occurs, unlike at other carbon-based electrode materials. Quantification was carried out using cyclic voltammetry, differential pulse voltammetry, and square-wave voltammetry. Linear ranges were determined (up to 21 mu mol L-1 with cyclic voltammetry) as well as limits of detection (0.15 mu mol L-1 by differential pulse voltammetry). Four different types of commercial samples were successfully analyzed. Recovery tests were performed which agreed with those obtained by spectrophotometric evaluation. The advantages of this electrode material for repetitive analyzes, due to the fact that no electrode surface renewal is needed owing to the lack of adsorption, are highlighted.

Development and Application of a Highly Selective Biomimetic Sensor for Detection of Captopril, an Important Ally in Hypertension Control

A biomimetic sensor is proposed as a promising new analytical method for determination of captopril in different classes of samples. The sensor was prepared by modifying a carbon paste electrode with iron (II) phthalocyanine bis(pyridine) [FePe(dipy)] complex. Amperometric measurements in a batch analytical mode were first carried out in order to optimize the sensor response. An applied potential lower than 0.2 V vs Ag vertical bar AgCl in 0.1 mol L(-1) of TRIS buffer at pH 8.0 provided the best response, with a linear range of 2.5 x 10(-5) to 1.7 x 10(-4) mol L(-1). A detailed investigation of the selectivity of the sensor, employing seventeen other drugs, was also performed. Recovery studies were carried out using biological and environment samples in order to evaluate the sensor`s potential for use with these sample classes. Finally, the performance of the biomimetic sensor was optimized in a flow injection (FIA) system using a wall jet electrochemical cell. Under optimized flow conditions, a broad linear response range, from 5.0 x 10(-4) to 2.5 x 10(-2) mol L(-1), was obtained for captopril, with a sensitivity of 210 +/- 1 mu A L mol(-1).

Electrochemical Behavior of Verapamil at Graphite-Polyurethane Composite Electrodes: Determination of Release Profiles in Pharmaceutical Samples

A solid graphite-polyurethane composite electrode has been used to determine release profiles of verapamil, a calcium-channel blocker. The electro-oxidation process was characterized by cyclic voltammetry and electrochemical impedance spectroscopy and showed no adsorption of analyte or oxidation products, unlike at other carbon-based electrodes. Quantification gave linear ranges up to 40molL-1 with cyclic voltammetry and detection limits of 0.7molL-1 by differential pulse and square-wave voltammetry. Commercial product samples were successfully analyzed with results equal to those from spectrophotometry. Because no electrode surface renewal is needed, this electrode material has many advantages.

Analytical methodology for the determination of urea: current practice and future trends

The determination of urea is important in a wide range of fields, including clinical diagnostics, environmental monitoring and food science. Numerous analytical techniques have been developed for the determination of urea, with no single technique dominant in all areas because of the diversity of applications. An overview of the existing analytical methodologies for urea is presented, and some new approaches are discussed, particularly those based on chemiluminescence detection to improve the sensitivity and the selectivity for the determination of this important analyte.

Synthesis and preliminary analytical evaluation of the chemiluminescence from (4-[4-(dichloromethylsilanyl)-butyl]-4`-methyl-2,2`-bipyridyl)bis(2,2`-bipyridyl)ruthenium(II) covalently bonded to silica particles

This paper describes, for the first time, a simple and effective synthetic route for covalently bonding the chemiluminescence reagent, (4-[4-(dichloromethylsilanyl)-butyl]-4’-methyl-2,2’-bipyridyl)bis(2,2’-bipyridyl)ruthenium(II) onto silica particles. The subsequent preparation of chemically regeneratable detection cells and their preliminary analytical evaluation with both sequential injection analysis and flow injection analysis are also reported. Unoptimised analytical figures of merit were established for standard solutions of codeine and sodium oxalate with detection limits calculated from three times the standard deviation of the blank signal, of 1 × 10^–8 M and 3 × 10^–7 M respectively. The chemically immobilised reagent exhibited some intriguing solvent and kinetic effects, which are also briefly discussed.

The determination of urea in soil extracts and related samples - a review

Although the dominant methods for the determination of urea in clinical applications incorporate selective enzymatic hydrolysis of urea, the determination of urea in soil extracts is complicated by the presence of urease inhibitors. The spectrophotometric determination of urea with an acidic solution diacetyl monoxime and semicarbazide is a viable option but traditional manual procedures are time-consuming. New variations on these procedures, based on microplates or flow-injection analysis methodologies, allow a far greater number of samples to be analysed with high precision and sensitivity.

Chemiluminescence methods for the determination of ofloxacin

Ofloxacin is a synthetic fluoroquinolone antibiotic that has been used in the treatment of respiratory tract, urinary tract and tissue-based infections. Methodology for the determination of ofloxacin based on chemiluminescence detection can be divided into: direct oxidation with tris(2,2′-bipyridyl)ruthenium(III) or permanganate; and enhancement of the emission from either the oxidation of sulfite or the reaction between sodium nitrite and hydrogen peroxide. In this paper, we compare the analytical methodology and evaluate the light-producing pathways that have been proposed for these reactions.

Determination of selected neurotransmitter metabolites using monolithic column chromatography coupled with chemiluminescence detection

The oxidation of selected clinically important neurotransmitter metabolites with acidic potassium permanganate in the presence of polyphosphates evokes chemiluminescence of sufficient intensity to enable the sensitive determination of these species. Limits of detection for 5-hydroxyindole-3-acetic acid (5-HIAA), vanilmandelic acid (VMA; α,4-dihydroxy-3-methoxybenzeneacetic acid), 4-hydroxy-3-methoxyphenylglycol (MHPG), homovanillic acid (HVA, 4-hydroxy-3-methoxyphenylacetic acid) and 3,4-dihydroxyphenylacetic acid (DOPAC) were between 5 × 10⁻⁹ and 4 × 10⁻⁸ M, using flow-injection analysis methodology. In addition, we demonstrate the rapid determination of homovanillic acid and 5-hydroxyindole-3-acetic acid in human urine – without the need for extraction procedures – using monolithic column chromatography with chemiluminescence detection.

A rapid test for heroin (3,6-Diacetylmorphine) based on two chemiluminescence reactions

A rapid method for screening drug seizure samples for 3,6-diacetylmorphine (heroin), which consists of a simple hydrolysis procedure and flow-injection analysis with two chemiluminescence reagents, is described. Before hydrolysis, 3,6-diacetylmorphine evokes an intense response with a tris(2,2'-bipyridyl)ruthenium(III) reagent (prepared by dissolving the perchlorate salt in acetonitrile), and a relatively weak chemiluminescence response with a second reagent: potassium permanganate in an aqueous acidic polyphosphate solution. However, the permanganate reagent is extremely sensitive toward the hydrolysis products of 3,6-diacetylmorphine (i.e., 6-monoacetylmorphine and morphine). Some compounds commonly found in drug laboratories may cause false positives with tris(2,2'-bipyridyl)ruthenium(III), but do not produce the markedly increased response with the permanganate reagent after the hydrolysis procedure. The combination of these two tests therefore provides an effective presumptive test for the presence of 3,6-diacetylmorphine, which we have verified with 14 samples obtained from a forensic science laboratory.

The determination of urea in wine – a review

The concentration of urea in wine is not routinely measured in Australian laboratories, but has been examined in studies of yeast metabolism and the formation of ethyl carbamate, a known carcinogen. For alcoholic beverages that may contain high levels of urea, steps have been taken to reduce the concentration of urea and therefore prevent ethyl carbamate production. Methods for the determination of urea in wine can be grouped into three categories that indicate how selectivity for urea is achieved; those based on colour-forming reactions, enzymatic hydrolysis and chromatographic separation. The two dominant methods used by research groups over the past fifteen years for the determination of urea in wine are based on the urea/ammonia test kit available from Boeringer Mannheim/R-Biopharm and the reaction of urea with 1-phenyl-1,2-propanedione-2-oxime; both are time-consuming and labour-intensive, but involve relatively straightforward and well-established procedures. However, other options are available that may be better suited to the desired application and the instrumentation available in any particular laboratory.

Soluble manganese(IV) as a chemiluminescence reagent for the determination of opiate alkaloids, indoles and analytes of forensic Interest

We present the results of our investigations into the use of soluble manganese(IV) as a chemiluminescence reagent, which include a significantly faster method of preparation and a study on the effect of formaldehyde and orthophosphoric acid concentration on signal intensity. Chemiluminescence detection was applied to the determination of 16 analytes, including opiate alkaloids, indoles and analytes of forensic interest, using flow injection analysis methodology. The soluble manganese(IV) reagent was less selective than either acidic potassium permanganate or tris(2,2′-bipyridyl)ruthenium(III) and therefore provided a more universal chemiluminescence detection system for HPLC. A broad spectral distribution with a maximum at 730 ± 5 nm was observed for the reaction between the soluble manganese(IV) and a range of analytes, as well as the background emission from the reaction with the formaldehyde enhancer. This spectral distribution matches that reported for chemiluminescence reactions with acidic potassium permanganate, where a manganese(II) emitting species was elucidated. This provides further evidence that the emission evoked in reactions with soluble manganese(IV) also emanates from a manganese(II) species, and not bimolecular singlet oxygen as suggested by previous authors.

Determination of synephrine in weight-loss products using high performance liquid chromatography with acidic potassium permanganate chemiluminescence detection

Adrenergic amines found in extracts of Citrus aurantium (bitter orange) evoke analytically useful chemiluminescence with acidic potassium permanganate in the presence of polyphosphates. From corrected chemiluminescence spectra, the wavelength of maximum intensity for these reactions was 680 ± 5 nm and, using flow injection analysis methodology, limits of detection for synephrine, octopamine, tyramine and hordenine were found to be between 1 × 10⁻⁹ and 1 × 10⁻⁸ M. We have applied this method of detection to the rapid determination of synephrine in dietary supplements using monolithic column chromatography.

A hybrid FIA/HPLC system incorporating monolithic column chromatography

We have combined the generation of solvent gradients using milliGAT pumps, chromatographic separations with monolithic columns and chemiluminescence detection in an instrument manifold that approaches the automation and separation efficiency of HPLC, whilst maintaining the positive attributes of flow injection analysis (FIA), such as manifold versatility, speed of analysis and portability. As preliminary demonstrations of this hybrid FIA/HPLC system, we have determined six opiate alkaloids (morphine, pseudomorphine, codeine, oripavine, ethylmorphine and thebaine) and four biogenic amines (vanilmandelic acid, serotonin, 5-hydroxyindole-3-acetic acid and homovanillic acid) in human urine, using tris(2,2′-bipyridyl)ruthenium(III) and acidic potassium permanganate chemiluminescence detection.

Chemiluminescence detection of opium poppy (papaver somniferum) alkaloids

A review with 98 references. The determination of the opium poppy (Papaver somniferum) alkaloids and their semi-synthetic derivatives has important applications in industrial process monitoring, clinical analysis and forensic science. Liquid-phase chemiluminescence reagents such as tris(2,2′-bipyridyl)ruthenium(II) and acidic potassium permanganate exhibit remarkable sensitivity and complementary selectivity for many P. somniferum alkaloids, which has been exploited in the development of a range of analytical procedures using flow analysis, high-performance liquid chromatography, capillary electrophoresis and microfluidic instrumentation.