Energy Transfer Electrogenerated Chemiluminescence for the Determination of Sulfite

A simple and novel electrogenerated chemiluminescence (ECL) method for the determination of sulfite has been developed based on the energy transfer ECL process. It was found that a weak ECL signal of sulfite was electrochemically generated on a platinum electrode in neutral aqueous solution. The signal was strongly enhanced by rhodamine B as an energy receptor and further enhanced by the neutral surfactant Tween 80. In 0.10M phosphate buffer solution (pH=7.5) containing 2.0×10^–6gmL^–1 rhodamine B and 0.4% (v/v) Tween 80, the ECL response to the concentration of sulfite at a potential of 0.82V was linear over a range of 1.0×10^–7gmL^–1 to 8.0×10^–6gmL^–1, and the detection limit was 5×10^–8gmL^–1. The relative standard deviation (n=11, 1.0×10^–6gmL^–1) was 3.8%. The proposed method has been successfully applied to the determination of sulfite in pharmaceutical injections and white sugar samples.     

Application of L-Cysteine-Capped ZnS Nanoparticles in the Determination of Nucleic Acids Using the Resonance Light Scattering Method

Nanometer-sized L-cysteine-capped ZnS particles were synthesized by a colloidal aqueous method. The functionalized nanoparticles are water-soluble and suitable for biological applications. In Tris-HCl buffer solution, nucleic acids combine with cysteine-capped nano-ZnS particles by intermolecular forces to form larger nanoparticles. There are two resonance light scattering peaks at 304.5nm and 373.8nm, respectively. The enhanced RLS is related to the concentration of nucleic acids in the range of 0.04 to 1.2µgmL^–1 for calf thymus DNA and 0.2 to 1.0µgmL^–1 for fish sperm DNA. The detection limits (3) are 19ngmL^–1 for calf thymus DNA and 23ngmL^–1 for fish sperm DNA, respectively. Four synthetic samples were analyzed satisfactorily.     

Determination of Picogram-Levels of Acetylspiramycin in Human Urine and Serum by Flow Injection Chemiluminescence

A sensitive chemiluminescence method for the determination of acetylspiramycin is presented. It is based on the greatly enhancive effect of acetylspiramycin on the chemiluminescence reaction between luminol and hydrogen peroxide in the flow system. The increase in chemiluminescence intensity was linearly proportional to the acetylspiramycin concentration in the range from 10pg·mL^–1 to 2.0ng·mL^–1 (r²=0.9979). The detection limit was 3pg·mL^–1 (3). At a flow rate of 2.0mL·min^–1, the process of determination, including sampling and washing, could be performed in 0.5 min, and the relative standard deviations of seven replicates are less than 5.0%. The proposed method was applied successfully to the determination of acetylspiramycin in pharmaceutical preparations, human urine and serum without pre-treatment. It was found that the excretive ratio of acetylspiramycin reached its maximum 2.0 hours after having been administered orally, and the excretive ratio in 12.0 hours was 8.4.     

The Fluorescent Reaction Between Quinaldine Red and Nucleic Acids and its Application to Fluorescent Assay of DNA and RNA

The reaction between quinaldine red (QR) and nucleic acids was studied. The free QR alone has no fluorescence in solution. However, it becomes fluorescent after binding to nucleic acids, giving maximum emission at 607nm with maximum excitation at 557nm. Maximum fluorescence intensity is produced in the pH range of 3.2–3.6. Based on the fluorescent reactions, a novel fluorometric method was developed for rapid determination of nucleic acids using QR as the fluorescent probe. Under optimal conditions, the calibration graphs were linear in the range of 0–30.0µgmL^–1 for CT DNA and 0–20.0µgmL^–1 for yeast RNA. The limits of detection were 38ngmL^–1 for CT DNA and 142ngmL^–1 for yeast RNA. Four synthetic samples were determined with satisfaction.Received December 20, 2002; accepted March 27, 2003 Published online August 8, 2003     

Development of an FI-ICP Method for On-Line Preconcentration and Determination of Platinum

This paper presents a new simple and rapid procedure for the preconcentration and determination of platinum. It is based on the adsorption of the metal ion and preconcentration on a micro-column (3cm×3mm) placed in the injection valve of a flow injection (FI) manifold and packed with 1,5-bis[(2-pyridyl)-3-sulphophenyl-methylene]thiocarbonohydrazide (PSTH) immobilised on an anion-exchange resin (Dowex 1X8-200). The metal was eluted from the column using a solution of 2M HNO₃. Various parameters and chemical variables affecting the preconcentration and determination of this metal by ICP-AES were evaluated. Five variables (sample flow rate, eluent flow rate, nebulizer flow rate, buffer concentration and mixing coil length) were considered as factors in the optimisation process. Interactions between analytical factors, and their optimal levels were investigated using two level factorial and central matrix designs. The optimum conditions established were applied to the determination of platinum by flow injection inductively coupled plasma atomic emission spectrometry (FI-ICP-AES). The method has a linear calibration range of 25 to at least 200ngmL^–1 with a detection limit of 7.4ngmL^–1 (S/N=3) and a throughput of 10 samples h^–1 using 5min. preconcentration time. The precision of the method (RSD) was 3.06% ngmL^–1 at the 50ngmL^–1 level of Pt(IV) and 2.93% at the 150ngmL^–1 level. The accuracy of the method was examined by determining the analyte content in spiked waters and by analysing an automobile catalyst standard reference material. The results show good agreement with the certified value and sufficiently high recoveries.     

Determination of Nucleic Acids Based on their Resonance Light Scattering Enhancement Effect on Metalloporphyrin Derivatives

A new method for the determination of nucleic acids at nanogram per mL level is proposed based on the enhanced resonance light scattering (RLS) signal resulting from the interaction of metalloporphyrins with nucleic acids. Under optimum conditions, the weak RLS signal of metalloporphyrin is enhanced by nucleic acids, and the enhanced RLS intensity is proportional to the concentration of nucleic acids. The detection limits of calf thymus DNA were 3.5ngmL^–1, 2.9ngmL^–1 and 1.0ngmL^–1 for three metalloporphyrins, respectively. Synthetic samples were determined with satisfactory results.     

Application of Functionalized Ag Nanoparticles for the Determination of Proteins at Nanogram Levels Using the Resonance Light Scattering Method

A novel method for the determination of proteins in aqueous solutions has been developed based on the enhancement of resonance light scattering (RLS) of Ag nanoparticles in the presence of proteins. Factors including acidity of the media, concentration of Ag hydrosol, reaction time, temperature, and interference of non-protein substances were investigated. Under the optimal conditions, with the enhanced RLS signals at 452nm, the linear ranges of calibration curves were 0–0.8µgmL^–1 for bovine serum albumin (BSA), 0–1.2µgmL^–1 for human serum albumin (HSA), and 0–2.5µgmL^–1 for human -IgG (-IgG), respectively. The detection limits were 1.3ngmL^–1 for BSA, 10ngmL^–1 for HAS, and 5.7ngmL^–1 for -IgG.This method has been applied to the analysis of synthetic samples and real human serum samples, and the results were in good agreement with those reported by the hospital, indicating that the method presented here is not only sensitive and simple, but also reliable and suitable for practical applications.     

Simple and Sensitive Assay for Nucleic Acids Using their Quenching Effect on the Chemiluminescence Reaction Between Luminol and Hydrogen Peroxide with Manganese-Tetrasulfonatophthalocyanine as a New Catalyst

The manganese-tetrasulfonatophthalo-cyanine (MnTSPc) catalyzed luminol-hydrogen peroxide chemiluminescence (CL) system can be quenched in the presence of nucleic acids. A new and highly sensitive CL quenching method for determining nucleic acids in aqueous solutions has been developed. Under optimum conditions, linear relationships were found between the quenched intensity of CL and the concentration of nucleic acids in the range 0.10–2.0µgmL^–1 for calf thymus DNA and 0–1.6µgmL^–1 for fish sperm DNA. The limits of detection were 14.8ngmL^–1 for calf thymus DNA and 21.7ngmL^–1 for fish sperm DNA. The relative standard deviation (RSD) of nine replicate measurements is 1.4% for 1.0µgmL^–1 calf thymus DNA. The method was applied to the analysis of nucleic acids in synthetic samples and the results are satisfactory.Received December 2, 2002; accepted June 2, 2003 published online September 1, 2003     

Determination of Nucleic Acids Based on Shifting the Association Equilibrium between a Heptamethine Cyanine Dye and Poly-Lysine

A near-infrared (near-IR) fluorescence recovery method for the determination of nucleic acids is presented. This method employs a two-reagent system composed of anionic heptamethines cyanine (HMC) and polycationic poly-lysine. The fluorescence of HMC, with maximum excitation and emission wavelengths at 778 and 804nm, respectively, was quenched by poly-lysine in proper concentration, but recovered by adding nucleic acids. Under optimal conditions, the recovered fluorescence was proportional to the concentration of nucleic acids. The calibration graphs are linear over the range of 5–300ngmL^–1 for herring sperm DNA (FS DNA), 2–100ngmL^–1 for calf thymus DNA (CT DNA) and 5–500ngmL^–1 for snake ovum RNA (SO RNA). The corresponding detection limits are 1.49ngmL^–1 for FS DNA, 0.7ngmL^–1 for CT DNA and 1.61ngmL^–1 for SO RNA, respectively. Four synthetic and three real nucleic acid samples were determined with satisfactory results.     

Solid-Phase Extraction and Spectrophotometric Determination of Trace Amounts of Mercury in Natural Samples

A sensitive and selective solid phase spectrophotometric method for the determination of trace amounts of inorganic mercury is described. Hg²⁺ was sorbed on a silica gel-packed column as an Hg²⁺–N,N-bis(2-mercaptophenyl)ethanediamide (H₂L) complex. The Hg²⁺ complex was eluted from the column using 7mL of acetone. Various parameters including pH, column flow rate, and ligand concentration were optimized. The complex was found to obey Beers law from 2.3 to 73.7µgmL^–1 within the optimum range when the preconcentration factor was two. The effective molar absorption coefficient at 523nm was 1.17×10³Lmol^–1cm^–1 at 523nm. The concentration limits in Beers law dropped from 0.09 to 2.95µgmL^–1 within the optimum range when the preconcentration factor was 50. The relative standard deviation at a concentration level of 5µgmL^–1 Hg²⁺ (9 repetitive determinations) was 1.6%. The detection limits are 0.34µgmL^–1 and 0.015µgmL^–1 when the preconcentration factors are 2 and 50, respectively. The method has been used for routine determination of trace levels of Hg²⁺ in natural waters. The potential application of this method for the removal of Hg²⁺ from natural samples (sea water and lake water) spiked with 100ngmL^–1 of Hg²⁺ was studied. In order to validate the proposed method, LGC 6156 (harbour sediment – extractable metals) was analysed by this method. The results proved that excellent extraction of Hg²⁺ from both natural water samples was obtained by solid phase extraction using N,N-bis(2-mercaptophenyl) ethanediamide.     

Catalytic Determination of Trace Formaldehyde with a Flow Injection System Using the Indicator Reaction between Crystal Violet and Bromate

A sensitive flow injection method is proposed for the determination of formaldehyde based on its catalytic action upon the redox reaction between crystal violet and potassium bromate in phosphoric acid medium. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of crystal violet injected at the maximum absorption wavelength of 600nm. A calibration graph from 0.018 to 1.400µgmL^–1 is obtained, and the detection limit is 0.007µgmL^–1 in a sample volume of 30µL. Up to 15 samples can be analyzed per hour with a relative standard deviation of 1.2 and 2.3%, respectively, for the determination of 1.0 and 0.1µgmL^–1 of formaldehyde. The method is free from most interference. This method has been applied to the determination of formaldehyde in air, decoration boards and paints, and the results compare well with those provided by iodimetry.     

Determination of Proteins at Nanogram Levels Using the Resonance Light Scattering Technique with a Novel PVAK Nanoparticle

A novel functionalized polyvinyl alcohol keto-derivative nanoparticle (PVAK) has been prepared in a one-step method using oxidation and degradation under ultrasonic irradiation. The nanoparticle is water-soluble, chemically stable, non-toxic and biocompatible. The surface of the nanoparticle is covered with abundant hydroxyl, carbonyl and carboxyl. At pH 3.0, the interactions of PVAK with different proteins can result in obviously enhanced RLS signals at 380nm. Under optimal conditions, the calibration graphs are linear over the range of 0.024.0µgmL^–1 for human serum albumin (HSA), 0.023.5µgmL^–1 for bovine serum albumin (BSA), and 0.053.5µgmL^–1 for human -globulin (-G), respectively. Detection limits were 6.4ngmL^–1 for HSA, 9.2ngmL^–1 for BSA, and 12.5ngmL^–1 for -G, respectively. The method was employed for the determination of total proteins in human serum with satisfactory results.     

Preparation and Application of a Novel Core-Shell Organic Nanoparticle as a Fluorescence Probe in the Determination of Nucleic Acids

A novel type of core-shell organic nanoparticles (pyrene/poly-acrylic acid; PAA) has been prepared by precipitation polymerization under ultrasonic irradiation. It was characterized by transmission electron microscopy (TEM) and fluorescence lifetime. The lifetime is about 5µs, which is much longer than conventional organic dyes fluorescence lifetime. As the surface of the core-shell organic nanoparticles is covered with abundant carboxylic groups, the nanoparticles are water-soluble, stable and biocompatible. At pH 6.4, maximum fluorescence is produced, with the maximum excitation and emission wavelengths of 338nm and 397nm, respectively. Under optimum conditions, the calibration graphs are linear over the range of 4.0×10^–51.0×10^–2mgmL^–1 for calf thymus DNA (ct-DNA) and 2.0×10^–41.0×10^–2mgmL^–1 for fish sperm DNA (fs-DNA). The detection limits were 3.6×10^–5mgmL^–1 and 1.4×10^–4mgmL^–1 for ct-DNA and fs-DNA, respectively. The method was applied to the determination of ct-DNA and fs-DNA in synthetic samples and the results were satisfactory. The method is sensitive, stable, rapid and tolerant towards most interfering substances.     

Determination of Na,K, Rb and Cs Distribution in Human Brain Using Neutron Activation Analysis

This study aims to investigate the distribution of Na, K, Rb and Cs in human brains (5 individuals, 12 brain parts, mean age: 75 years). Distribution of the trace metals between lipid fraction and brain tissue was investigated in solvent extraction experiments. Determinations were carried out by instrumental neutron activation analysis. The present results show a rather non-homogeneous distribution for Na and a relatively uniform distribution for K, Rb and Cs. The mean concentrations found are 7440µgNag^–1 dry weight, 12800µgKg^–1, 14µgRbg^–1 and 50ngCsg^–1. A highly significant positive correlation was found between Rb and Cs. Solvent extraction experiments showed that 19% of Rb and 26% of Cs of the total content is located in lipid fraction.     

Application of Lanthanide-Sensitised Chemiluminescence to the Determination of Levofloxacin, Moxifloxacin and Trovafloxacin in Tablets

A flow injection method including chemiluminescence detection has been developed and applied to the determination of fluoroquinolones levofloxacin, moxifloxacin and trovafloxacin in tablets. The proposed method is based on the luminescent properties of the system Ce(IV)–sulphite–fluoroquinolone and the addition of a trivalent lanthanide ion as emission-sensitizer. The optimum conditions for chemiluminescence emission were investigated for each fluoroquinolone. The best results were achieved when employing Eu(III) as lanthanide cation for levofloxacin and moxifloxacin, and Tb(III) for trovafloxacin. These fluoroquinolones were determined over the concentration range of 0.5–3.5µgmL^–1, 0.2–3.0µgmL^–1 and 0.008–0.400µgmL^–1, with detection limits of 0.100, 0.035 and 0.008µgmL^–1, respectively. The relative standard deviations were in the range of 1.0–2.5% for all three cases. The method was applied to the determination of three fluoroquinolones in their respective pharmaceutical preparations and compared with an independent UV-spectrophotometric method. The results were satisfactory.     

Electrochemical Behavior of Epinephrine at a Penicillamine Self-Assembled Gold Electrode,and its Analytical Application

The fabrication and electrochemical characteristics of a penicillamine (PCA) self-assembled monolayer modified gold electrode were investigated. The self-assembled electrode shows obvious electrocatalytic activity for the oxidation of epinephrine (EP). In phosphate buffer (pH 7.73), a sensitive oxidation peak was observed at 0.190V with the PCA modified Au electrode. The peak current is proportional to the concentration of EP in the range of 2.0×10^–56.0×10^–4molL^–1 and 5.0×10^–6 2.0×10^–4molL^–1 for cyclic voltammetry (CV) and differential pulse voltammetry (DPV) with the detection limits of 1.8×10^–7 and 1.3×10^–7molL^–1, respectively. The possible reaction mechanism is also discussed. The PCA self-assembled monolayer modified gold electrode is highly stable and can be applied to the determination of EP in practical injection samples. Application is simple, rapid and produces accurate results.     

Kinetic Spectrophotometric Determination of Total Iron in Natural Water by Flow Injection Analysis Using On-Line Preconcentration

A new flow injection catalytic spectrophotometric method for on-line preconcentration and determination of total iron in natural water is described. The method is based on a combination of iron-catalyzed oxidation of diaminoditolyl by potassium bromate and the use of on-line preconcentration of iron onto 8-hydroxy-quinoline immobilized on silica gel. The corresponding calibration graph is linear over the range of 2.0–110ngmL^–1 for Fe(III) using a time-based technique for 5min preconcentration. The relative standard deviation of 11 measurements of 60ngmL^–1 Fe(III) was 0.67%. The method was applied to the determination of iron in natural water. The results obtained by the proposed method were compared with those obtained by ICP-AES. The t-test showed no significant differences between the two methods at a confidence level of 95%.     

High-Performance Liquid Chromatographic Determination of Quinolizidine Alkaloids in Radix Sophora Flavescens Using Tris(2,2′-Bipyridyl)Ruthenium(II) Electrochemiluminescence

Electrogenerated chemiluminescences (ECLs) of quinolizidine alkaloids including matrine (MT), sophocarpine (SC), and sophoridine (SRI) are studied. The light emission is caused by an electro-oxidation reaction between Ru(bpy)₃²⁺ and the tertiary amino group on the alkaloid compounds. A thin-layer flow cell equipped with a glassy carbon disk electrode (22.1mm²) at the potential of ⁺1.30V (vs. Ag/AgCl) was applied for ECL observation. MT, SC and SRI were separated and quantitatively determined within 25min by an ODS-80 Ts reversed-phase column with a mobile phase containing 80mmolL^–1 NaH₂PO₄–K₂HPO₄ buffer+acetonitrile (7:3)+40mmolL^–1 sodium dodecyl sulfate (pH 6.5). The determination limit at an S/N of 3 ranged from 3×10^–9gmL^–1 for MT, 6×10^–9gmL^–1 for SC and 1×10^–9gmL^–1 for SRI. The recoveries are from 92 to 108%, with repeatability ranging from 1.3 to 4.5% (relative standard deviation). The method was successfully applied to the determination of quinolizidine alkaloids in Sophora flavescens samples.     

Kinetics of formation,dissociation and equilibrium constants of pentacyanoaquoruthenate(II) with heterocycles

The kinetics of formation and dissociation reactions of [Ru(CN)₅L]^3– with a series of heterocyclic ligands were studied in aqueous media. In this presence of an excess of heterocycle, the observed second order rate constants were calculated from the k_obs versus [ligand] plot at =0.100m NaClO₄. Activation parameters for the formation reactions (H=28±7kJmol^–1 and S=140±35JK^–1mol^–1) are comparable for all systems, indicating a common mechanism. The kinetics of exchange of coordinated heterocycles for 1,3,5-triazine yielded a rate saturation typical of a limiting dissociative mechanism. Activation parameters of the limiting first order specific rate of dissociation reactions were H=85±7kJmol^–1 and S=18±4JK^–1mol^–1. Equilibrium constants were calculated from the second order rates of formation and pseudo-first order rates of dissociation reaction.     

2,3-Dihydroxypyridine Loaded Amberlite XAD-2 (AXAD-2-DHP): Preparation, Sorption–Desorption Equilibria with Metal Ions, and Applications in Quantitative Metal Ion Enrichment from Water, Milk and Vitamin Samples

2,3-Dihydroxypyridine loaded (via –N=N–linker) Amberlite XAD-2 (AXAD-2-DHP) was prepared and characterized by elemental analyses, TGA and FT-IR spectra. It (1g packed in a column of 1cm diameter; surface area 135.5m²g^–1) was found to be an effective solid phase sorbent for enriching Zn²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Co²⁺ at pH 3.5 to 7.0 using flow rates between 1.0–5.0mLmin^–1. For desorption (recovery 97.0–99.8%) of the metal ions, 8 to 10mL of 2.0molL^–1 HCl or 1.5molL^–1 HNO₃ at a flow rate of between 2.0 and 4.0mLmin^–1 were found most suitable. The t_1/2 (time for 50% sorption) is between 2 and 10min when a 50mL solution (containing a total amount of metal of 2mg) was equilibrated with 0.5g of resin. Sorption of all metal ions except Pb²⁺ follows the Langmuir model, whereas for Pb the data fits with the Freundlich model. The sorption capacity is between 60.7 (for Cd) and 406.7 (for Cu) µmolg^–1. The resin can withstand an acid concentration of 6molL^–1 and can be reused for thirty cycles of sorption–desorption. The preconcentration factor varies between 100 and 300. For Cd, Ni and Cu the sorption capacity of 2,3-dihydroxypyridine loaded cellulose is lower than that of the present resin. The tolerance limits of electrolytes, humic acid, complexing agents, Ca²⁺ and Mg²⁺ in the enrichment of all metal ions are reported. The limits of detection are 3.88, 5.37, 8.72, 13.88, 4.71, 1.24, 0.59 and 0.30µgL^–1 for Zn²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Co²⁺, respectively. The calibration curves for flame AAS determination were linear in the ranges 0.018–1.0, 0.067–5.0, 0.2–5.0, 0.9–20, 0.028–2.0, 0.077–5.0, 0.19–10 and 0.1–3.5µgmL^–1, respectively. All the eight metal ions in river and synthetic water samples, Co in vitamin tablets and Zn in milk samples have been quantitatively enriched with Amberlite XAD-2-DHP and determined by flame atomic absorption spectrometry.