Chemiluminescence determination of tetracycline based on radical production in a basic acetonitrile–hydrogen peroxide reaction

A Selective Fluorescent Nanoprobe Based on Graphene Quantum Dots and Hg2+ for the Determination of Tetracycline in Biological Samples

A simple, sensitive, and selective fluorometric method based on graphene quantum dots and Hg²⁺ is presented for the determination of tetracycline. The fluorescence emission of graphene quantum dots at 463 nm decreased in the presence of Hg²⁺ ions due to its electrostatic interaction with the negatively charged surface of quantum dots at pH = 8.0. The addition of tetracycline to this system resulted in the retrieval of the fluorescence emission of the graphene quantum dots proportional to the tetracycline concentration. This is because of the interaction between tetracycline and Hg²⁺ that results in the release of the quantum dots' surface. Under the optimized conditions, the calibration curve indicated good linearity in the range of 2.0-44.0 nmol L^-1 with a detection limit of 0.52 nmol L^-1 for tetracycline. The designed nanoprobe was capable of the determination of tetracycline in serum and urine samples.

Rational Design of a Highly Dispersed Fe-N-C Nanosheet with 1,10-Phenanthroline-2,9-Dicarboxylic Acid as a Preorganized Ligand: Boosted Electrochemiluminescence Detection of Tetracycline

In view of the shortcomings of the current coreactant electrochemiluminescence (ECL) and inspired by natural oxygen (O₂) reduction metalloenzymes, a novel ECL amplification strategy was established. A pyrolytic iron- and nitrogen-doped (Fe-N-C) nanosheet rich in singly ionized oxygen vacancy (V_O^•) defects was rationally designed by destroying the highly saturated coordination with a preorganized ligand 1,10-phenanthroline-2,9-dicarboxylic acid (PDA). Extraordinary catalytic activity for O₂ activation was obtained via screening a special pyrolysis temperature using spectroscopic and electrochemical methods. The high-spin ferric centers of highly dispersed FeC nanoclusters and abundant carbon and oxygen vacancy defects fully contributed to the inherent catalytic activity. ECL amplification was achieved by integrating the material with luminol to generate redox-active radicals in situ from dissolved O₂ and simultaneously shorten the transferring distance of radicals. Tetracycline (TC), which posed a growing threat to aquatic biodiversity and environmental safety, as a model antibiotic was successfully detected with a detection limit of 3.88 nM (S/N = 3), clarifying a promising application prospect of this new effective ECL amplification strategy in biological analysis and environmental monitoring.

A Simple and Novel Sensor for the Determination of Acetamiprid Based on Its Reducing Effect on the Chemiluminescence of S, N-CQDs in CH3CN-H2O2 System

A simple and novel method for the determination of acetamiprid in water samples is suggested. The method is based on the reducing effect of acetamiprid on the chemiluminescence intensity of new sulfur and nitrogen co-doped carbon dots (S, N-CQDs) in an acetonitrile-hydrogen peroxide (CH₃CN-H₂O₂) system. The possible mechanism was investigated, and it was found that S, N-CQDs react with (¹O₂)₂*, produced from the CH₃CN-H₂O₂ reaction, leading to excited state S, N-CQDs, which deactivate to the ground state by photon emission. Acetamiprid diminishes the chemiluminescence (CL) intensity by competing with S, N-CQDs. The CL intensity reduction is proportional to the concentration of acetamiprid. S, N-CQDs were easily prepared by a hydrothermal method. Under the optimal conditions, a linear range of 2.5 - 25.0 μg L^-1 with a detection limit (3σ) of 0.4 μg L^-1 was obtained. This method was successfully applied to the determination of trace amounts of residual pesticides in water samples.

Europium Doped Silicon Quantum Dot As a Novel FRET Based Dual Detection Probe: Sensitive Detection of Tetracycline, Zinc, and Cadmium

The imbalance of Zn²⁺ /Cd²⁺ in the human body can lead to many serious diseases due to the overuse of antibiotics and deposition in animal products. Developing a functional material for detecting is challenging and in demand. Herein, silicon quantum dots (SiQDs) are designed as a functional platform for the detection of tetracycline and Zn²⁺ /Cd²⁺ . The COOH functionalized SiQDs with the emission wavelength of 450 nm are chelated with Eu(NO₃ )₃ to form SiQDs-Eu³⁺ ratio fluorescent probes, which can be used to detect tetracycline (TCs) and Zn²⁺ /Cd²⁺ by fluorescence resonance energy transfer (FRET) principle sequentially. The fluorescent probe showed good linearity between ion concentration and fluorescence enhancement. The detection limit of TCs and Zn²⁺ /Cd²⁺ are 0.2 × 10^-6  m and 3 × 10^-6  m, respectively, when the pH of the solution is 7.4. In addition, the synthesized SiQDs-Eu³⁺ exhibited good stability (from 94.9% to 103.1%). The relative standard deviations (RSD, n = 10) of human serum and urine were both less than 3%. Therefore, the SiQDs-Eu³⁺ ratio fluorescence probe will provide a good application prospect in actual sample detection.

A nanofluidic device for ultrasensitive and label-free detection of tetracycline in association with γ-cyclodextrin and GO

Herein, an ultrasensitive and selective nanofluidic device for tetracycline (TC) was developed in association with γ-cyclodextrin and graphene oxide (GO). The assay was designed based on the change of the nanochannel surface charge due to the selective recognition ability of GO between aptamers and TC-aptamer complexes. And γ-cyclodextrin was utilized to eliminate the excess TC since the amine group molecules were inclined to be adsorbed onto the nanochannel surface and affected the adsorption efficiency of the nanochannel. In the presence of TC, TC specifically binded to the aptamer to form TC-aptamer and was separated from GO. The TC-aptamer complexes could be quantitated with conical nanochannels coated with polyethyleneimine (PEI)/Zr4+. The redundant TC was removed by γ-cyclodextrin. The detection limit of the nanofluidic device was as low as 2 ng L-1 (S/N = 3) and the linear range was 10 ng L-1 to 10 μg L-1. Moreover, the nanofluidic device provided high specificity and good recovery rates of 94.8-109.3% in natural river, tapwater and wastewater samples. The results revealed that our study provided a new rapid detection method for trace contaminant analysis.

A dual-response ratiometric fluorescent sensor by europium-doped CdTe quantum dots for visual and colorimetric detection of tetracycline

Residues in animal food and drinking water caused by the abuse of antibiotics lead to cell resistance and many chronic diseases in the human body. Therefore, it has become an inevitable trend to develop a fast, easy-to-use, on-site/real-time visualization method for the detection of antibiotics. Herein, we report a dual-response ratiometric fluorescence sensor which is fabricated by chelating europium ions (Eu³⁺) onto cadmium telluride quantum dots (CdTe QDs) for real-time and visible detection of tetracycline (TC). With the TC addition, the fluorescence of probe can be seen by the naked eye, from green to yellow and finally to red, exhibiting a dosage-sensitive and broad-chromatic detection strategy for TC. The fluorescence intensity ratio of I₆₁₆/I₅₁₂ of Eu/CdTe QDs sensor displays a good linear relation to TC concentrations in the range of 0-80 μM with a limit of detection (LOD) of 2.2 nM. In addition, the sensor can visually detect 200 nM TC in actual samples, which is lower than the maximum residue limit (MRL) of the safety standard. The methodology reported here opens a window toward the real applications of fluorescent and shows the wide applicability in pursuing the concepts simple, rapid, visual, and real-time for food safety and environmental protection.

Just Add Luminol to Turn the Spotlight on Radziszewski Amidation

Radziszewski amidation, namely the peroxide-mediated conversion of nitriles into amides, is a chemiluminescent reaction involving singlet oxygen. Its increasing relevance in green chemistry and analytical chemistry makes it an important subject to be discussed in advanced chemistry courses. To turn the attention of lecturers, teachers, and students toward this reaction, the history of its discovery as well as its practical applications is discussed. Moreover, a simple and effective experiment to demonstrate the chemiluminescent properties of Radziszewski amidation is provided.

Facile one-pot synthesis of visible light-responsive BiPO4/nitrogen doped graphene hydrogel for fabricating label-free photoelectrochemical tetracycline aptasensor

It is fundamental to develop highly efficient visible light-responsive photoelectrochemical (PEC) performance material for fabricating PEC biosensor. Herein, BiPO₄/three-dimensional nitrogen doped graphene hydrogel (3DNGH) nanocomposites were prepared for the first time via a facile one-pot hydrothermal route. In this nanoarchitecture, the BiPO₄ nanorods were anchored onto the porous structure of 3DNGH. Compared with pristine BiPO₄, the absorption of BiPO₄/3DNGH has been extend to visible-light region, and the energy band gap of BiPO₄/3DNGH was calculated to be 2.10 eV, which was greatly narrower than that of pristine BiPO₄ with a band gap of 3.85 eV. Under visible light irradiation, the photocurrent signal of the as-prepared BiPO₄/3DNGH was 847.2-fold, 4.1-fold and 2.3-fold enhanced comparing to pristine BiPO₄, BiPO₄ functionalized reduced graphene oxide and BiPO₄/nitrogen doped graphene. The enhancement of such photocurrent signal was attributed to the introduction of 3DNGH, which was capable to improve the charge transfer rate and also the efficiency of visible-light utilization of BiPO₄. Based on the excellent PEC properties of BiPO₄/3DNGH, a label-free PEC aptasensor for selectivity and sensitivity detection of tetracycline (Tc) was successfully established by using Tc aptamer as a biorecognition element. Under optimized conditions, the proposed PEC aptasensor exhibited a wide linear in the range from 0.1 nmol L^-1 to 1 μmol L^-1 as well as a low detection limit of 0.033 nmol L^-1 (S/N = 3). The prepared BiPO₄/3DNGH nanocomposites would serve as a promising visible light-responsive photoactive material for fabrication of PEC biosensors with high performance.

Graphitic Carbon Nitride Sensitized with CdS Quantum Dots for Visible-Light-Driven Photoelectrochemical Aptasensing of Tetracycline

Graphitic carbon nitride (g-C₃N₄) is a new type of metal-free semiconducting material with promising applications in photocatalytic and photoelectrochemical (PEC) devices. In the present work, g-C₃N₄ coupled with CdS quantum dots (QDs) was synthesized and served as highly efficient photoactive species in a PEC sensor. The surface morphological analysis showed that CdS QDs with a size of ca. 4 nm were grafted on the surface of g-C₃N₄ with closely contacted interfaces. The UV-visible diffuse reflection spectra (DRS) indicated that the absorption of g-C₃N₄ in the visible region was enhanced by CdS QDs. As a result, g-C₃N₄-CdS nanocomposites demonstrated higher PEC activity as compared with either pristine g-C₃N₄ or CdS QDs. When g-C₃N₄-CdS nanocomposites were utilized as transducer and tetracycline (TET)-binding aptamer was immobilized as biorecognition element, a visible light-driven PEC aptasensing platform for TET determination was readily fabricated. The sensor showed a linear PEC response to TET in the concentration range from 10 to 250 nM with a detection limit (3S/N) of 5.3 nM. Thus, g-C₃N₄ sensitized with CdS QDs was successfully demonstrated as useful photoactive nanomaterials for developing a highly sensitive and selective PEC aptasensor.

A combination of β-cyclodextrin functionalized magnetic graphene oxide nanoparticles with β-cyclodextrin-based sensor for highly sensitive and selective voltammetric determination of tetracycline and doxycycline in milk samples

Highly sensitive and selective determination of tetracycline and doxycycline in milk samples using solid phase extraction followed by differential pulse voltammetric determination on a β-cyclodextrin modified carbon paste sensor.

Peroxide induced ultra-weak chemiluminescence and its application in analytical chemistry

Chemiluminescence (CL), as a sensitive, rapid, and facile analytical method, has been widely applied in environmental monitoring, clinical diagnosis and food safety. Recently, the main challenge and research interest in the CL study have been focused on exploring new CL systems and obtaining new insight into the interaction between CL reagents. The peroxide induced ultra-weak CL reactions are some new arising systems that have received great attention and have been successfully applied in many fields. The peroxide includes hydrogen peroxide, peroxynitrite, peroxymonocarbonate, peroxomonosulphate and so on. This review paper covers the mechanism of the peroxide induced ultra-weak CL and the analytical applications of the CL have also been summarized. The future prospects for the peroxide induced ultra-weak CL are discussed.

Enhancement of chemiluminescence of the KIO4-luminol system by gallic acid, acetaldehyde and Mn2+: application for the determination of catecholamines

Chemiluminescence (CL) from the oxidation of luminol with potassium periodate in strong alkaline solutions was greatly enhanced by the combined effect of gallic acid, acetaldehyde and Mn(2+). The CL spectra exhibited only one emission band at 425 nm, indicating 3-aminophthalate as the emitting species. Various scavengers for superoxide anion, hydroxyl radical and singlet oxygen quenched the CL emission very efficiently (74-100%), suggesting the possible involvement of these reactive oxygen species (ROS) in the CL reactions. It is postulated that oxidation of gallic acid and acetaldehyde by periodate catalyzed by Mn(2+) generates these ROS, which then react with luminol to enhance the CL emission. We also found that the enhanced CL emission was strongly inhibited by catecholamines, probably because of their effective scavenging of ROS. Based on this observation, a simple, rapid and sensitive new CL method was developed for the determination of catecholamines. The detection limits (3sigma) for dopamine, l-dopa, norepinephrine and epinephrine were 0.63, 1.37, 0.56 and 14.3 nmol/L, respectively. The linear range was 1-10 nmol/L; relative standard deviations were 0.71-1.34% for 0.1 micromol/mL catecholamines. This CL method was applied to the determination of catecholamines in pharmaceutical injections with satisfactory results.

Determination of photoirradiated tetracyclines in water by high-performance liquid chromatography with chemiluminescence detection based reaction of rhodamine B with cerium (IV)

A simple, selective and sensitive method has been developed for the simultaneous determination of tetracycline, oxytetracycline, chlorotetracycline, demeclocycline, doxycycline and meclocycline based on reversed-phase high-performance liquid chromatography with chemiluminescence detection. The procedure was based on the chemiluminescent enhancement by photoirradiated tetracyclines of the cerium (IV)-rhodamine B system in sulphuric acid medium. The six tetracyclines were separated on an Aquasil-C18 column with a gradient elution using a mixture of acetonitrile and 0.1 mol L(-1) phosphate buffer as mobile phase, photoderivatized using a photoreactor consisting of a tube reactor coil of PFA and a 8W Xenon lamp. Under the optimized conditions, the method was validated with respect to linearity, precision, limits of detection and quantification and accuracy. The relative standard deviation (RSD) on intra-day precision was below 10% and detection limits ranged between 0.12 and 0.34 microg L(-1). The proposed method has been successfully applied to the determination of tetracyclines in surface water samples. A possible mechanism of the chemiluminescence in the system is discussed.

Direct screening of tetracyclines in water and bovine milk using room temperature phosphorescence detection

A fast and simple flow-through optosensor was designed and characterized for the direct screening of four tetracycline (TCC) antibiotics (tetracycline, oxytetracycline, chlortetracycline and doxycycline) in water and bovine milk samples. The proposed optosensor provides rapid binary yes/no overall responses, being appropriate for the screening of this family of antibiotics above or below a pre-set concentration threshold. The experimental set-up is based on a flow-injection manifold coupled on-line to a phosphorescence detector. Aliquots of the samples are pretreated with Eu(III) to form room temperature phosphorescent metal chelates and injected in the flow manifold. Those chelates are then on-line retained on a conventional flow-cell (packed with polymeric Amberlite XAD-4 particles) which is placed inside the cell holder of the phosphorimeter. After the emission is registered, the antibiotic-metal complexes are eluted from the packed resin with 1M HCl (for milk samples a second regeneration step, using methanol, should be performed). A sample throughput of about 20 samples per hour was obtained. Optimum experimental conditions include a pH 9, a Eu(III) concentration of 2 x 10(-4) M and 8 mM sodium sulphite as chemical deoxygenant. The phosphorescence emitted by the europium-TCC complexes was measured at 394 and 617 nm for excitation and emission wavelengths, respectively. The unreliability region, given by the probability of false positives and false negatives, respectively (set at 5% in both cases) was in the range between 0.2 and 11.6 nM for detection of tetracyclines in water samples (at a cut-off level of 4 nM) and in the range between 165 and 238 nM for detection of tetracyclines in milk (cut-off level fixed at the normative EU level of 200 nM). Finally, the applicability of the proposed screening optosensor was tested for the reliable control of tetracyclines in contaminated and uncontaminated water and milk samples.

New method for the photo-chemiluminometric determination of benzoylurea insecticides based on acetonitrile chemiluminescence

The viability of tandem photochemical reaction-chemiluminescence detection has been studied for the determination of five benzoylurea insecticides, namely, diflubenzuron, triflumuron, hexaflumuron, lufenuron and flufenoxuron. The 'on-line' photochemical reaction of benzoylurea pesticides provides an enhanced chemiluminescence response of the pesticides during their oxidation by potassium hexacyanoferrate(III) and sodium hydroxide, whose signal increases with the percentage of acetonitrile in the reaction medium. The determination was performed using a photoreactor consisting of a PFA (perfluoroalkoxy) tube reactor coil (5 mx1.6-mm O.D. and 0.8-mm I.D.) and an 8-W xenon lamp. As the yield of the photoderivatization process and the chemiluminescent signals depend on the percentage of acetonitrile, the chromatographic column (a Gemini C18, Phenomenex 150 mmx4.6 mm, 5-microm particle size) was chosen with the aim of using high percentages of this organic solvent in the mobile phase. Previous studies showed that the rate of the chemiluminescent reaction was very fast. Therefore, a modification was carried out in the detector in order to mix the analytes and reactants as near as possible to the measure cell. The optimised method was validated with respect to linearity, precision, limits of detection and quantification accuracy. Under the optimised conditions, linear working range extends three orders of magnitude with the relative standard deviation of intra-day precision below 10% and detection limits between 0.012 and 0.18 microg mL-1, according to the compound. The proposed method has been successfully applied to the determination of benzoylureas in cucumber with good results.

Flow Injection Chemiluminescence Determination of Imipramine in Tablets, Human Plasma and Urine Samples Based upon Oxidation with Singlet Oxygen Generated in N-Bromosuccinimide-Hydrogen Peroxide Reaction

Singlet oxygen generated in a reaction between N-bromosuccinimide and hydrogen peroxide was used for the chemiluminescence oxidation of imipramine. A strong chemiluminescence signal was observed when imipramine was mixed with N-bromosuccinimide and hydrogen peroxide under an alkaline condition. The chemiluminescence signal was linearly dependent on the concentration of imipramine in the range of 0.01 - 1.0 mg/L. The detection limit was 0.005 mg/L imipramine and the relative standard deviation was 1.5% for a 0.4 mg/L imipramine solution in 11 repeated measurements. The proposed method was successfully applied to the determination of imipramine in tablets, human plasma and urine samples.

Direct chemiluminescence determination of ibuprofen by the enhancement of the KMnO4–sulphite reaction

A simple, rapid, flow-injection chemiluminescence (CL) method is described for the determination of ibuprofen. A strong CL signal was detected when a mixture of the analyte and sulphite was injected into acidic KMnO(4). The CL signal is proportional to the concentration of ibuprofen in the range 0.1-10.0 mg/L. The detection limit is 0.02 mg/L ibuprofen, the relative standard deviation is 1.8% (0.5 mg/L ibuprofen; n = 11) and the sample measurement frequency is 120/h. The proposed method was successfully applied to the determination of ibuprofen in pharmaceutical preparations and in spiked urine samples. The mechanism of the CL reaction is also discussed.

Flow injection chemiluminescence determination of nitrofurazone in pharmaceutical preparations and biological fluids based on oxidation by singlet oxygen generated in N-bromosuccinimide–hydrogen peroxide reaction

A simple flow injection chemiluminescence (FI-CL) method was proposed for the determination of nitrofurazone. Strong CL signal was generated during the reaction of nitrofurazone with H(2)O(2) and N-bromosuccinimide (NBS) in alkaline condition. The CL signal was proportional to the nitrofurazone concentration in the range 1.0 x 10(-7) to 1.0 x 10(-5) g mL(-1). The detection limit was 2 x 10(-8) g mL(-1) nitrofurazone and the relative standard deviation was less than 4% (6.0 x 10(-6) g mL(-1) nitrofurazone, n=11). The proposed method was successfully applied to the determination of nitrofurazone in compound furacillin nasal drops, human plasma and urine samples. The CL reaction mechanism was also discussed briefly. Singlet oxygen generated in the reaction between H(2)O(2) and NBS was suggested to be participated in the CL reaction.

Reduction in Antimicrobial Substantivity of MTAD After Initial Sodium Hypochlorite Irrigation

Potential intrinsic tetracycline staining of intraradicular dentin has been observed when BioPure MTAD was employed as the final irrigant after initial rinsing with NaOCl. This study examined the effect of NaOCl-MTAD interaction on the antimicrobial substantivity of MTAD in dentin. Dentin cores previously irrigated with either MTAD, or in conjunction with 1.3% NaOCl as an initial irrigant were placed on blood agar plates inoculated with Escherichia faecalis at 10(5) cfu/ml. Dentin cores irrigated with 1.3% NaOCl only, and autoclaved dentin disks were used as the respective positive and negative controls. After anaerobic incubation, the mean diameter of bacterial inhibition zones formed around the MTAD group was significantly larger than the NaOCl/MTAD group, which, in turn, was not significantly different from the NaOCl positive control. Oxidation of MTAD by NaOCl resulted in the partial loss of antimicrobial substantivity in a manner similar to the peroxidation of tetracycline by reactive oxygen species.

Molecularly imprinted on-line solid-phase extraction combined with flow-injection chemiluminescence for the determination of tetracycline

A molecularly imprinted polymer solid phase extraction (MISPE) method combined with flow-injection chemiluminescence (FI-CL) for the determination of residual tetracycline (TC) in fish samples is presented. The molecularly imprinted polymer (MIP) of TC was synthesized and particles of this MIP were packed into a polytetrafluoroethylene (PTFE) tube, which was connected into the sampling loop of an eight-way injection valve and served as the MISPE column for on-line selective adsorption of TC. The eluent (CH3CN : HNO3 (0.01 mol L(-1)) = 4 ratio 1, v ratio v) was used for extracting the adsorbed TC, which could be detected by its good enhancing effect on the CL reaction between Ce(iv) and rhodamine B. The CL intensity is linear to TC concentration in the range from 4 x 10(-9) to 4 x 10(-7) g mL(-1). The detection limit is 1 x 10(-9) g mL(-1) (3 sigma) and the relative standard deviation is 2.4% (n = 9). The conditions of preconcentration, extraction and CL reaction were carefully studied. The selectivity experiment shows that the selectivity and sensitivity of the CL method could be improved greatly when MIP was used as a recognition material in SPE. However, the MISPE column interacted indiscriminately with oxytetracycline (OTC) with a 49 +/- 2% binding. An intermediate differential pulsed elution (DPE) step using 3% acetic acid as eluent was employed to remove OTC and other interfering substances. The proposed MISPE-CL method has been applied successfully to the determination of TC in fish samples. At the same time, the binding characteristics of the polymer to tetracycline were evaluated by batch and dynamic methods.

Determination of nine pyrethroid insecticides by high-performance liquid chromatography with post-column photoderivatization and detection based on acetonitrile chemiluminescence

An HPLC method was developed to determine pyrethroids, including fenpropathrin, beta-cyfluthrin, lambda-cyhalothrin, deltamethrin, fenvalerate, permethrin, acrinathrin, tau-fluvalinate, and bifenthrin, by coupling HPLC, post-column irradiation with UV light and chemiluminescence detection of the resulting photoproducts. It is based on the observation that photolyzed pyrethroids take part in a chemiluminescent reaction in presence of K3Fe(CN)6 and NaOH, whose signal increases with the percentage of acetonitrile in the reaction medium. As the yield of the photoderivatization process and the chemiluminescent signals depend on the percentage of acetonitrile, the chromatographic column (a Gemini C18, Phenomenex 150 mm x 4.6 mm, 5 microm particle size) was chosen with the aim of using high percentages of this organic solvent in the mobile phase. Previous studies showed that the rate of the chemiluminescent reaction was very fast. Therefore, a modification was carried out in the detector in order to mix the analytes and reactives as near as possible to the measure cell. The optimised method was validated with respect to linearity, precision, limits of detection and quantification accuracy. Under the optimised conditions, linear working range extends three orders of magnitude with the relative standard deviation on intra-day precision below 10% and detection limits between 0.013 and 0.049 microg mL(-1), according to the compound. The proposed method has been successfully applied to the determination of pyrethroids in tomato with good results.

Determination of tetracycline, chlortetracycline and oxytetracycline by flow injection with inhibitory chemiluminescence detection using copper(II) as a probe ion

This paper reports an indirect flow-injection (FI) method for the determination of the tetracycline drugs (TCs), tetracycline (TC), chlortetracycline (CTC) and oxytetracycline (OTC), using copper(II) as a probe ion. The method was based on the inhibition caused by these TCs to the copper(II)-catalysed chemiluminescence (CL) reaction between luminol and H(2)O(2). The CL reaction was induced on-line and injection of the sample produced negative peaks as a result of the copper(II) complexation or displacement by the analytes. The height of the peaks was proportional to the drug concentration in the sample. The choice of the catalyst ion, the concentration of luminol, H(2)O(2) and copper(II) are discussed. The linear range was 3.6 x 10(-8)-1.0 x 10(-5), 1.1 x 10(-7)-1.0 x 10(-5) and 1.9 x 10(-7)-1.0 x 10(-5) mol/L for TC, CTC and OTC, respectively. The detection limit was 5.0 x 10(-9) mol/L for TC, 1.0 x 10(-8) mol/L for CTC and 2.0 x 10(-8) mol/L for OTC (3sigma), respectively. The method was applied to the determination of TCs in pharmaceutical preparations and human urine with recoveries in the range 95-105%.

Investigation on the interaction between dihydroxybenzene and Fe3+–H2O2–Rh6G system based on enhancing chemiluminescence

A highly sensitive flow-injection chemiluminescence (FI-CL) method has been developed for the determination of dihydroxybenzene, based on the hydroxyl radical reaction. Hydroxyl radical (.OH) produced by the reaction of Fe(3+) and H(2)O(2) oxidize rhodamine 6G to produce weak CL. It was observed that catechol and hydroquinone greatly enhanced the weak CL reaction. However, the proposed CL system is not suitable for determination of resorcinol because the enhancement reaction is very slow. The proposed procedure has a linear range of 0.01-2 mg/L for catechol, with a detection limit of 0.006 mg/L, and 0.008-1 mg/L for hydroquinone, with a detection limit of 0.004 mg/L. The possible mechanism of the CL system is discussed.

Hairy roots of Helianthus annuus: a model system to study phytoremediation of tetracycline and oxytetracycline

The release of antibiotics to the environment has to be controlled because of serious threats to human health. Hairy root cultures of Helianthus annuus (sunflower), along with their inherent rhizospheric activity, provide a fast growing, microbe-free environment for understanding plant-pollutant interactions. The root system catalyzes rapid disappearance of tetracycline (TC) and oxytetracycline (OTC) from aqueous media, which suggests roots have potential for phytoremediation of the two antibiotics in vivo. In addition, in vitro modifications of the two antibiotics by filtered, cell- and microbe-free root exudates suggest involvement of root-secreted compounds. The modification is confirmed from changes observed in UV spectra of exudate-treated OTC. Modification appears to be more dominant at the BCD chromophore of the antibiotic molecule. Kinetic analyses dismiss direct enzyme catalysis; the modification rates decrease with increasing OTC concentrations. The rates increase with increasing age of cultures from which root exudates are prepared. The decrease in modification rates upon addition of the antioxidant ascorbic acid (AA) suggests involvement of reactive oxygen species (ROS) in the antibiotic modification process.

Determination of tetracyclines residues in honey using high-performance liquid chromatography with potassium permanganate–sodium sulfite–β-cyclodextrin chemiluminescence detection

A novel method was developed for the simultaneous determination of tetracycline antibiotic (TCA) residues such as oxytetracycline (OTC), tetracycline (TC), and metacycline (MTC) by high-performance liquid chromatography (HPLC) coupled with chemiluminescence (CL) detection. The procedure was based on the chemiluminescent enhancement by TCAs of the potassium permanganate-sodium sulfite-beta-cyclodextrin system in a phosphoric acid medium. The separation was carried out with an isocratic elution using a mixture of acetonitrile and 0.001 M phosphoric acid. For the three TCAs, the detection limits at a signal-to-noise of 3 ranged from 0.9 to 5.0 ng/ml. The relative standard deviations for the determination of TCAs ranged from 3.1 to 7.4% within a day (n=11) and ranged from 2.2 to 8.6% in 3 days (n=9), respectively. The method was successfully applied to the determination of TCA residues in honey samples. The possible mechanism of the CL reaction was also discussed.

Flow injection analysis of tetracyclines using inhibited Ru(bpy)32+/tripropylamine electrochemiluminescence system

Tetracyclines (TCs) were found to strongly inhibit the electrochemiluminescence (ECL) from the Ru(bpy)3(2+)-tripropylamine system when a working Pt electrode was maintained at 1.05 V (vs. Ag/AgCl) in pH 8.0 carbonate buffer solution. On this basis, a flow injection (FI) procedure with inhibited electrochemiluminescence detection has been developed for the determination of tetracycline (TC) and oxytetracycline (OTC). Under the optimized condition, the linear ranges of 2.0 x 10(-8)-1.0 x 10(-5) and 1.0 x 10(-8)-1.0 x 10(-5) g/mL and the detection limits of 4.0 x 10(-9) and 3.8 x 10(-9) g/mL were obtained for TC and OTC, respectively. The relative standard deviations (RSD) were 0.68% and 1.18% for 5.0 x 10(-7) g/mL TC and OTC (n = 13), respectively. The method showed higher sensitivity than most of the reported methods. It was successfully applied to the determination of tetracycline in a Chinese proprietary medicine, Tetracyclini and Cortisone Eye Ointment, and the residues of tetracycline in honey products. The inhibition mechanism has been proposed due to an energy transfer between electrogenerated Ru(bpy)3(2+)* and benzoquinone derivatives at the electrode surface.

Electroanalysis of Tetracycline Using Nickel-implanted Boron-doped Diamond Thin Film Electrode Applied to Flow Injection System

The electrochemical analysis of tetracycline was investigated using nickel-implanted boron-doped diamond thin film electrode by cyclic voltammetry and amperometry with a flow injection system. Cyclic voltammetry was used to study the electrochemical oxidation of tetracycline. Comparison experiments were carried out using as-deposited boron-doped diamond thin film electrode (BDD). Nickel-implanted boron-doped diamond thin film electrode (Ni-DIA) provided well-resolved oxidation irreversible cyclic voltammograms. The current signals were higher than those obtained using the as-deposited BDD electrode. Results using nickel-implanted boron-doped diamond thin film electrode in flow injection system coupled with amperometric detection are presented. The optimum potential for tetracycline was 1.55 V versus Ag/AgCl. The linear range of 1.0 to 100 microM and the detection limit of 10 nM were obtained. In addition, the application for drug formulation was also investigated.

Oxytetracycline inactivation by putative reactive oxygen species released to nutrient medium ofHelianthus annuus hairy root cultures

When subjected to stress, plants produce reactive oxygen species (ROS) as a part of the defense response. The oxidative response is also used to degrade organic pollutants. Hairy roots of Helianthus annuus (sunflower) are shown to oxidize oxytetracycline (OTC) through the action of the ROS released to the nutrient medium by the hairy root cultures. Methyl jasmonate (MeJA) elicits ROS formation in the hairy root cultures. The activities of the antioxidant enzymes, ascorbate peroxidase (APX), catalase (CAT), and guaiacol peroxidase (GPX), are reported for hairy root cultures treated with increasing concentrations of MeJA. A bioassay using Enterococcus hirae as the test microorganism demonstrates the root-catalyzed oxidation process results in conversion of OTC into product(s) devoid of antibiotic activity. Direct evidence for putative ROS oxidation of OTC is obtained by mass spectrometry (MS) and HPLC/MS showing first quinone formation followed possibly by ring cleavage, which disrupts UV absorption and destroys antibiotic activity.