Chemiluminescence determination of atenolol in biological fluids by a europium-sensitized permanganate-sulfite system

A simple flow injection chemiluminescence (CL) method was developed for the determination of atenolol using Eu³⁺ as the probe. It was found that the weak CL generated by the KMnO₄-Na₂SO₃ reaction can be significantly enhanced by the atenolol-Eu³⁺ complex. The experimental conditions were optimized. The CL intensity was linearly related to atenolol concentration in the range from 8.0 × 10⁻⁹ to 1.0 × 10⁻⁵ g mL⁻¹. The detection limit (3s _b) was 3 × 10⁻⁹ g mL⁻¹ and the relative standard deviation for 1.0 × 10⁻⁷ g mL⁻¹ atenolol solution was 2.4% (n = 11). The method has high sensitivity, wide linear range, inexpensive instrumentation, and has been applied to the determination of atenolol in spiked human urine and plasma samples with recoveries within the range 95.5–104.0%. Supplementary material to this paper is available in electronic form at Electronic supplementary material: Discussion of the reaction mechanism and additional figures are available online as electronic supplementary material (ESM) at . Correspondence: Jianxiu Du, Key Laboratory of Analytical Chemistry for Life Science of Shaanxi Province, School of Chemistry and Materials Science, Shaanxi Normal University, Xi’an 710062, P.R. China     

Flow injection on-line hydrophobic sorbent extraction for flame atomic absorption spectrometric determination of cadmium in water samples

A flow injection system was developed for on-line sorbent extraction preconcentration and flame atomic absorption spectrometric determination of cadmium in natural water samples. The non-charged cadmium complex with diethyl-dithiophosphate (DDPA) was formed on-line in 0.1 mol L⁻¹ HNO₃ and retained on the hydrophobic poly-chlorotrifluoroethylene (PCTFE) sorbent material. The adsorbed complex was eluted with isobutyl methylketone (IBMK) and injected directly into the nebulizer via a flow compensation unit. All major chemical and flow parameters affecting the complex formation adsorption and elution as well as interference were studied and optimized. By processing 2.4 mL of sample, the enhancement factor was 39 and the sampling frequency was 50 h⁻¹. For 30 s preconcentration time the detection limit was 0.3 μg L⁻¹ and the relative standard deviation at 5.0 μg L⁻¹ Cd concentration level was 2.9%. The calibration curve was linear in the range 0.8–40.0 μg L⁻¹. The accuracy of the method was estimated by analyzing a certified reference material NIST-CRM 1643d (Trace elements in water). Good recoveries were obtained for spiked natural-water and waste-water samples. Correspondence: Aristidis N. Anthemidis, Laboratory of Analytical Chemistry, Department of Chemistry, Aristotle University, GR-Thessaloniki 54124, Greece     

Design of a field flow system for the on-line spectrophotometric determination of phosphate, nitrite and nitrate in natural water and wastewater

This study describes the design and optimisation of a field flow system for the in-situ collection and on-line determination of phosphate, nitrate and nitrite by flow injection analysis-spectrophotometry. The method is based on the initial determination of phosphate as its phosphoantimonylmolybdenum blue complex which is then oxidized on-line by nitrite and the decrease in absorbance is monitored at 880 nm. Nitrate is determined as the difference between total and initial nitrite content in a separate flow after reduction to nitrite in a cadmium reductive column. The calibration curves were linear in the range 0–2.00 mg L⁻¹ P-phosphate, 0–10.00 mg L⁻¹ nitrite and 0–7.00 mg L⁻¹ nitrate with correlation coefficients of 0.9979, 0.9993 and 0.9995, respectively. The detection limits, calculated as 3S/N, were 0.15 mg L⁻¹ for P-phosphate, 0.17 mg L⁻¹ for nitrite and 0.09 mg L⁻¹ for nitrate. The reproducibility was below 3.0% (n = 7). Method validation in the analysis of natural water and wastewater samples revealed that it can efficiently be applied to the determination of the target analytes, with recoveries in the range of 92–108%. Correspondence: Athanasios G. Vlessidis, Laboratory of Analytical Chemistry, Department of Chemistry, University of Ioannina, Ioannina 45110, Greece     

Electrochemical determination of uric acid using a mesoporous SiO2-modified electrode

A mesoporous SiO₂-modified carbon paste electrode for the determination of uric acid is described. Owing to the regular and specific mesoporous channels, numerous active sites and a large surface area, the mesoporous SiO₂-modified electrode greatly increases the oxidation peak current of uric acid. Based on this, a highly sensitive, rapid and convenient electrochemical method was developed for the determination of uric acid after optimizing the experimental parameters (supporting electrolyte, content of mesoporous SiO₂, accumulation potential and time). The linear range is from 2.5 × 10⁻⁷ to 2.0 × 10⁻⁵ mol L⁻¹, and the limit of detection is estimated to be 8.0 × 10⁻⁸ mol L⁻¹. The relative standard deviation for 10 mesoporous SiO₂-modified electrodes is 5.8%. The method was used to determine uric acid in human serum samples. Correspondence: Kangbing Wu, Department of Chemistry, Huazhong University of Science and Technology, Wuhan 430074, P.R. China     

Preconcentration technique for manganese by adsorption onto a tantalum wire for tungsten tube atomizer electrothermal atomization atomic absorption spectrometry

A multi-pumping flow system for the spectrophotometric determination of nitrite and nitrate is described. The determination of nitrite is based on the Griess-Ilosvay reaction. Nitrate can be determined after its on-line reduction to nitrite using hydrazine sulphate in alkaline medium. Calibration was linear up to 3 mg NO₂ ⁻ L⁻¹ with a limit of detection (3s_b/S) of 0.013 mg NO₂ ⁻ L⁻¹ an injection throughput of 55 injections h⁻¹ and a repeatability (RSD) of 0.5% for the direct determination of nitrite. Two calibration graphs within the ranges 0.039–7 mg NO₃ ⁻ L⁻¹ and 0.026–5 mg NO₂ ⁻ L⁻¹ were run for the determination of nitrate and nitrite under reducing conditions, respectively. A limit of detection of 0.039 mg NO₃ ⁻ L⁻¹ was obtained. An injection throughput of 27 injections h⁻¹ and an RSD lower than 1.5% were achieved. The method was successfully applied to the determination of nitrite and nitrate in water samples. Correspondence: Víctor Cerdà, Department of Chemistry, University of the Balearic Islands, Carretera de Valldemossa Km7.5, 07122 Palma de Mallorca, Spain     

A simple spectrophotometric technique for determination of Irganox 1010 in polymeric samples

A simple spectrophotometric method is presented for the determination of tetrakis [methylene (3,5-di-tert-butyl-4-hydroxyhyrocinnamate)] methane (Irganox 1010) in polymeric samples. To a solution of Irganox 1010 in acetone is added concentrated sodium hydroxide solution and then it is shaken for a short time. The 2-phase system produced in the upper phase (acetone) is yellow colored. Absorbance of the colored phase is recorded in a quartz cell at 440 nm. Different parameters such as temperature, time after mixing solutions of Irganox 1010 and sodium hydroxide, and concentration of sodium hydroxide are studied. The linear dynamic range, limit of detection and correlation coefficient (r) are 25–1000 mg·L⁻¹, 10 mg·L⁻¹ and 0.996, respectively. The repeatability of this method is good (n = 6, C = 250 mg·L⁻¹, RSD = 3.26%). Correspondence: Mir Ali Farajzadeh, Department of Analytical Chemistry, Faculty of Chemistry, Tabriz University, Tabriz, Iran     

Chemiluminescence Method for the Determination of Glutathione in Human Serum Using the Ru(phen)3 2+ – KMnO4 System

A simple, rapid and specific chemiluminescence (CL) method for the determination of glutathione has been developed. The method is based on the enhanced CL of the reaction between Ru(phen)₃ ²⁺ (phen = 1,10-phenanthroline) and KMnO₄ by glutathione in HCl medium. Under the optimum conditions, the response is linearly proportional to the concentration of glutathione between 1.5 × 10⁻⁷ and 1.0 × 10⁻⁵ mol L⁻¹. The dection limit for glutathione (5.8 × 10⁻⁸ mol L⁻¹) is about 10 and 200 times better than those of the spectrophotometric method using Ellman regent and the Lucigenin – CL method, respectively. The final procedure allows the determination of glutathione in human serum with recoveries of 92%–108%. A satisfactory agreement was obtained with a mean relative difference of 2.5% compared to the HPLC method.     

HPLC determination of cefotaxime and cephalexine residues in milk and cephalexine in veterinary formulation

An HPLC method was developed and validated for the determination of the cephalosporins cefotaxime and cephalexine in skimmed bovine milk. The analytical column, Kromasil C₁₈ (250 mm × 4.0 mm, 5 μm) was operated at ambient temperature. Mobile phase consisted of CH₃OH-acetate buffer (pH = 4.0) and it was delivered isocratically at a flow rate of 1.0 mL · min⁻¹. Total analysis time was less than 5 min. Caffeine was used as internal standard (5 ng · μL⁻¹). UV detection was performed at 265 nm. Method validation was performed by means of intra-day (n = 5) and inter-day accuracy and precision (n = 8), sensitivity and linearity. Limits of detection (LOD) and limits of quantification (LOQ) were 0.1 and 0.3 ng · μL⁻¹, respectively. The method was applied to the analysis of a veterinary drug (CEPOREX) containing cephalexine. The results were quite accurate with the relative error varying from −8.0 to −3.5%. Solid-phase extraction was applied to remove all matrix interference from milk samples. High extraction recoveries (average 84–121%) were achieved by using Abselut NEXUS cartridges with acetonitrile as eluent and a rinsing step with water and n-butanol. A pre-concentration step was necessary in a 1/10 level to reach the EU MRL concentration level (100 μg · kg⁻¹). RSD values were less than 7% for both cephalosporins. Correspondence: Ioannis N. Papadoyannis, Laboratory of Analytical Chemistry, Department of Chemistry, Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece     

Ultrasensitive Assay of Rhein in Medicine Based on its Enhanced Luminol-K3Fe(CN)6 Chemiluminescence Reaction Using the Flow Injection Technique

Determination of the effective components in traditional Chinese medicine is one of the key steps for its identification. In this paper a novel and sensitive chemiluminescence (CL) method for the determination of rhein coupled with flow-injection analysis (FIA) is developed. It is based on the strong sensitizing effect on the weak CL reaction between luminol and ferricyanide in alkaline solution. Under optimal experimental conditions, the relative CL intensity is proportional to the concentration of rhein in the range of 7.0 × 10⁻¹²–7.0 × 10⁻¹⁰ mol L⁻¹ and 1.0 × 10⁻⁹–4.0 × 10⁻⁵ mol L⁻¹, the detection limit is 1.478 × 10⁻¹³ mol L⁻¹, and the relative standard deviation (RSD) for 9 parallel measurements of 1.408 × 10⁻⁷ mol L⁻¹ rhein is 3.4%. The method was successfully applied to the determination of rhein in pharmaceutical preparations. The possible mechanism of CL is also briefly discussed.     

Covalent modification of glassy carbon electrode with cysteine for the determination of dopamine in the presence of ascorbic acid

A covalently modified glassy carbon electrode with cysteine has been fabricated via an electrochemical oxidation procedure and was applied to induce the electrochemical differentiation between dopamine (DA) and ascorbic acid (AA). Based on the electrostatic interactions between the negatively charged groups on the electrode surface and DA and AA, the modified electrode enhanced the oxidation of DA, reducing the overpotential by 180 mV, and hindered the oxidation of AA, shifting the oxidation potential positively by 170 mV. The peak current for DA at the modified electrode was greatly enhanced and that for AA was significantly decreased, which allows the determination of DA in the presence of AA. The differential pulse peak current was linearly dependent on DA concentration over the range of 5 × 10⁻⁶–2 × 10⁻⁴ mol L⁻¹. The detection limit was 1.8 × 10⁻⁶ mol L⁻¹. The selectivity and sensitivity for dopamine is due to charge discrimination and analyte accumulation. The modified electrode has been applied to the determination of DA in the presence of AA. Correspondence: L. Zhang, Department of Chemistry, College of Life and Environmental Science, Shanghai Normal University, Guilin Rd 100, Shanghai 200234, P.R. China     

Flow injection on-line preconcentration coupled to hydride generation atomic fluorescence spectrometry for ultra-trace amounts of cadmium determination in seawater

A simple flow injection on line separation and preconcentration system coupled to hydride generation atomic fluorescence spectrometry (HG-AFS) was developed for ultra-trace cadmium determination in seawater. With the sample pH kept at 3.0, the preconcentration of cadmium on the inner walls of the knotted reactor was carried out based on the retention of cadmium complex with 1-phenyl-3-methyl-4-benzoylpyrazol-5-one. A 0.2 mol L⁻¹ HCl was introduced to elute the retained analyte complex and merge with KBH₄ solution for HG-AFS detection. Under the optimal experimental conditions, an enhancement factor of 12 was obtained with a sample consumption of 12.0 mL. The limit of detection was 3.2 ng L⁻¹ with a sample frequency of 24 h⁻¹. The developed method was validated by the analysis of cadmium in certified reference materials, and was applied to the determination of cadmium in four seawater samples with R.S.D. of around 10%. Correspondence: Hong Wu, Department of Chemistry, Xuzhou Normal University, Xuzhou 221116, P.R. China     

Adsorption voltammetry of the zirconium-alizarin red S complex at a multi-walled carbon nanotubes modified carbon paste electrode

We used a carbon paste electrode modified with multi-walled carbon nanotubes as a working electrode and studied the electrochemical behavior of zirconium-alizarin red S complex on it. It was found that the modified electrode exhibited a significant catalytic effect toward the reduction of free alizarin red S and the complex. The second derivative linear scan voltammograms of the complex were recorded by a polarographic analyser from 0 to −1000 mV (vs. SCE), and it was found that the complex can be adsorbed on the surface of the modified electrode, yielding a peak at about −470 mV, corresponding to the reduction of alizarin red S in the complex. The linear range was found to be 2.0 × 10⁻¹¹–8.0 × 10⁻⁷ mol L⁻¹, and the detection limit was 1.0 × 10⁻¹¹ mol L⁻¹ (S/N = 3) for 3 min accumulation. The procedure was successfully applied to the determination of trace amounts of zirconium in the ore samples. Correspondence: Pei-Hong Deng, Department of Chemistry and Material Science, Hengyang Normal University, Hengyang Hunan 421008, P.R. China     

Chemiluminescence determination of chromium(III) and total chromium in water samples using the periodate-lucigenin reaction

A new chemiluminescence (CL) method combined with flow injection technique is described for the determination of Cr(III) and total Cr. It is found that a strong CL signal is generated from the reaction of Cr(III), lucigenin and KIO₄ in alkaline condition. The determination of total Cr is performed by pre-reduction of Cr(VI) to Cr(III) by using H₂SO₃. The CL intensity is linearly related to the concentration of Cr in the range 4.0 × 10⁻¹⁰–1.0 × 10⁻⁶ g mL⁻¹. The detection limit (3s _b) is 1 × 10⁻¹⁰ g mL⁻¹ Cr and the relative standard deviation is 1.9% (5.0 × 10⁻⁸ g mL⁻¹ of Cr(III) solution, n = 11). The method was applied to the determination of Cr(III) and total Cr in water samples and compared satisfactorily with the official method.     

Application of full factorial design for the preconcentration of chromium by solid phase extraction with Amberlyst 36 resin

The preconcentration of chromium(III) by solid phase extraction and its determination from aqueous solutions by flame atomic absorption spectrometry (FAAS) is investigated by applying an experimental design. The optimization of the preconcentration variables such as pH of the sample solution, flow rate of the sample solution and concentration of elution solution was carried out using 2³ full factorial design. The most important parameter affecting the preconcentration of chromium is the concentration of eluent. In the established experimental conditions, chromium can be determined with a relative standard deviation of 2.0% (N = 7) for a chromium concentration of 100 μg L⁻¹. The detection limit for chromium was 1 μg L⁻¹ (N = 20). The adsorption capacity of Amberlyst 36 is found to be 90.9 mg g⁻¹ for chromium. Effect of other ions on the procedure was also evaluated. The method was validated by the analysis of certified reference materials (tea leaves GBW 07605 and fish tissue IAEA-407). The method was applied to the determination of chromium in waste water, dam water, carrot, parsley and lettuce. Correspondence: Ali Rehber Türker, Department of Chemistry, Faculty of Science and Arts, Gazi University, TR-06500 Ankara, Turkey     

Determination of Yttrium by Resonance Light Scattering Technique

 Yttrium was determined by means of the resonance light scattering (RLS) technique. The characteristics of resonance light scattering spectra of yttrium-1, 6-bi(1′-phenyl-3′-methyl-5′-pyrazolone-4′-) hexanedione (BPMPHD), the effective factors and optimum conditions were studied. In the pH range of 5.0–6.1, yttrium-BPMPHD complex produces three characteristic peaks of RLS at 365, 402 and 467 nm. The enhanced intensity of RLS is proportional to the concentration of yttrium in the range of 1.0×10⁻⁸ to 1.0×10⁻⁵ mol · L⁻¹. The limit of detection is 5.9×10⁻⁹ mol · L⁻¹. The method has been used for the determination of Y³⁺ in mixed rare earths. Correspondence: Key Lab for Colloid and Interface Chemistry of Education Ministry, School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, People’s Republic of China. e-mail: wux@sdu.edu.cn Received July 3, 2002; accepted October 20, 2002     

Trace determination of clenbuterol with an MWCNT-Nafion nanocomposite modified electrode

A method for the determination of trace clenbuterol is described. Multi-walled carbon nanotubes (MWCNTs)-Nafion composite was used to modify the glassy carbon electrode (GCE). The modified electrode showed high sensitivity and good selectivity for clenbuterol detection. It offered a linear range of 1.0 × 10⁻⁹–1.0 × 10⁻⁶ mol · L⁻¹ with a detection limit of 5.0 × 10⁻¹⁰ mol · L⁻¹ in pH = 1.2 solution. The oxidation mechanism of clenbuterol on the electrode was also investigated. Correspondence: Xiao-Ya Hu, Department of Chemistry, Yang Zhou University, Yang Zhou, Jiang Su, P.R. China     

Sensitive fluorescent probes for determination of hydrogen peroxide and glucose based on enzyme-immobilized magnetite/silica nanoparticles

Sensitive fluorescent probes for the determination of hydrogen peroxide and glucose were developed by immobilizing enzyme horseradish peroxidase (HRP) on Fe₃O₄/SiO₂ magnetic core–shell nanoparticles in the presence of glutaraldehyde. Besides its excellent catalytic activity, the immobilized enzyme could be easily and completely recovered by a magnetic separation, and the recovered HRP-immobilized Fe₃O₄/SiO₂ nanoparticles were able to be used repeatedly as catalysts without deactivation. The HRP-immobilized nanoparticles were able to activate hydrogen peroxide (H₂O₂), which oxidized non-fluorescent 3-(4-hydroxyphenyl)propionic acid to a fluorescent product with an emission maximum at 409 nm. Under optimized conditions, a linear calibration curve was obtained over the H₂O₂ concentrations ranging from 5.0 × 10⁻⁹ to 1.0 × 10⁻⁵ mol L⁻¹, with a detection limit of 2.1 × 10⁻⁹ mol L⁻¹. By simultaneously using glucose oxidase and HRP-immobilized Fe₃O₄/SiO₂ nanoparticles, a sensitive and selective analytical method for the glucose detection was established. The fluorescence intensity of the product responded well linearly to glucose concentration in the range from 5.0 × 10⁻⁸ to 5.0 × 10⁻⁵ mol L⁻¹ with a detection limit of 1.8 × 10⁻⁸ mol L⁻¹. The proposed method was successfully applied for the determination of glucose in human serum sample.     

A novel method for the determination of Pb2+ based on the quenching of the fluorescence of CdTe quantum dots

A novel method for the determination of Pb²⁺ has been developed based on quenching of the fluorescence of thiol-capped CdTe quantum dots (QDs) by Pb²⁺ in aqueous solutions. Under optimum conditions, the relative fluorescence intensity was linearly proportional to the concentration of Pb²⁺ between 2.0 × 10⁻⁶ and 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 2.7 × 10⁻⁷ mol L⁻¹. The relative standard deviation (RSD) was 4.6% for a 4.0 × 10⁻⁵ mol L⁻¹ Pb²⁺ solution (N = 5). As an application, the proposed method was successfully applied to the analysis of Pb²⁺ in food samples, and the results were satisfactory, i.e. consistent with those of flame atomic absorption spectrometry (FAAS). Correspondence: Heyou Han, College of Science, Institute of Chemical Biology, State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, P.R. China     

Electrochemical behavior of lead(II) at poly(phenol red) modified glassy carbon electrode, and its trace determination by differential pulse anodic stripping voltammetry

Poly(phenol red) (denoted as PPR) films were electrochemically synthesized on the surface of a glassy carbon electrode (GCE) by cyclic voltammetry to obtain a chemically modified electrode (denoted as PPR-GCE). The growth mechanism of PPR films was studied by attenuated total reflection spectroscopy. This PPR-GCE was used to develop a novel and reliable method for the determination of trace Pb²⁺ by anodic stripping differential pulse voltammetry. At optimum conditions, the anodic peak exhibits a good linear concentration dependence in the range from 5.0 × 10⁻⁹ to 5.0 × 10⁻⁷ mol L⁻¹ (r = 0.9989). The detection limit is 2.0 × 10⁻⁹ mol L⁻¹ (S/N = 3). The method was employed to determine trace levels of Pb²⁺ in industrial waste water samples. Correspondence: Gongjun Yang, Ming Shen, College of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002, P.R. China     

Simple and Selective Spectrophotometric Method for the Determination of Iron (III) and Total Iron Content, Based on the Reaction of Fe(III) with 1,2-Dihydroxy-3,4-Diketocyclo-Butene (Squaric Acid)

 Squaric acid (1,2-dihydroxy-3,4-diketo-cyclobutene) is used in a specific reaction with Fe(III) for the spectrophotometric determination of Fe(III) and total iron content. The optimization of the experimental parameters leads to the establishment of a simple, fast and accurate analytical method. The analytical procedure includes mixing ammonium squarate (40 mM), prepared in a phthalate buffer solution of pH 2.7, with the sample and measuring the absorbance at 515 nm. The molar absorptivity of the colored product is 3.95×10³ L·mol⁻¹·cm⁻¹, at 515 nm. Calibration graphs for Fe(III) are rectilinear for 0.5–20 mgL⁻¹, with a detection limit of 0.3 mgL⁻¹ and r.s.d. not exceeding 2.5%, for five replicates of a 3.0 mgL⁻¹ standard solution. The method has been successfully applied to the determination of iron (III) and the total iron content after quantitative oxidation of iron (II). The results for several analyzed samples when compared with those acquired by using the FAAS technique, were found to be in satisfactory agreement. Author for correspondence: University of Ioannina, Department of Chemistry, Laboratory of Analytical Chemistry, Ioannina 451 10, Greece. E-mail: panavelt@cc.uoi.gr Received July 27, 2002; accepted December 20, 2002 Published online April 11, 2003