Flow injection determination of hydrogen peroxide using diperiodatoargentate- and diperiodatonickelate-luminol chemiluminescence

A novel chemiluminescence (CL) method for the determination of hydrogen peroxide is described. Method is based on the transition metals in highest oxidation state complex, which include diperiodatoargentate (DPA) and diperiodatonickelate (DPN) and show excellent sensitisation on the luminol-H₂O₂ CL reaction with low luminol concentration in alkaline medium. In particular, the sensitiser which was previously reported (such as Co²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Fe³⁺, Cr³⁺, KIO₄, K₃Fe(CN)₆ etc.) to be unobserved CL due to poor sensitisation with such low concentration of luminol which makes the method hold high selectivity. Based on this observation, the detection limits were 6.5?×?10^?9?mol?L^?1 and 1.1?×?10^?8?mol?L^?1 hydrogen peroxide for the DPN- and DPA-luminol CL systems, respectively. The relative CL intensity was linear with the hydrogen peroxide concentration in the range of 2.0?×?10^?8–6.0?×?10^?6?mol?L^?1 and 4.0?×?10^?8–4.0?×?10^?6?mol?L^?1 for the DPN- and DPA-luminol CL systems, respectively. The proposed method had good reproducibility with a relative standard deviation of 3.4% (8.0?×?10^?7?mol?L^?1, n?=?7) and 1.0% (2.0?×?10^?6?mol?L^?1, n?=?7) for the DPN- and DPA-luminol CL systems, respectively. A satisfactory result has been gained for the determination of H₂O₂ in rainwater and artificial lake water by use of the proposed method.     

Determination of Cr(VI) in the Presence of Complexing Agents and Humic Substances by Catalytic Stripping Voltammetry

The voltammetric method of Cr(VI) determination in a flow system is proposed. Determinations can be carried out in the simultaneous presence of an excess of Cr(III), complexing agents, humic substances and surfactants. The method is based on the combination of a selective accumulation of the product of Cr(VI) reduction to the metallic state and a very sensitive voltammetric method of chromium determination in the presence of DTPA and nitrates. The calibration graph is linear from 1×10^?9 to 5×10^?8 mol L^?1 for accumulation time of 30 s. The relative standard deviation is 5.2% (n=5) for Cr(VI) concentration 1×10^?8 mol L^?1. The influence of humic and fulvic acids, complexing agents and surfactants on Cr(VI) and the interfering Cr(III) signal is presented. The method was applied to Cr(VI) determination in certified reference material, soil sample, natural water sample and EDTA extracts from soil certified reference material.     

Direct chemiluminescence determination of fenbufen by the enhancement of the {\text{Ru}}\left( {{\text{phen}}} \right)_3^{2 + } –cerium(IV) system

A method is described for determination of fenbufen that is based on the chemiluminescence (CL) reaction of the ${\text{Ru}}\left( {{\text{phen}}} \right)_3^{2 + } $ –cerium(IV)–fenbufen system. An enhanced CL reaction was developed, and optimum conditions for CL were investigated. The CL was linearly dependent on fenbufen concentration in the range 4.0?×?10^?8–9.0?×?10^?6 mol L^?1. The detection limit was 2.0?×?10^?8 mol L^?1. The relative standard deviation (RSD) was 2.8% for eleven measurements of 6.0?×?10^?7 mol L^?1 fenbufen standard solution. The new method enables simple, sensitive, and rapid determination of fenbufen and has been used for determination of fenbufen in pharmaceutical preparations in capsule, spiked serum and urine samples.     

Speciation Analysis of Chromium by Adsorptive Stripping Voltammetry in Tap and River Water Samples

An adsorptive stripping voltammetric method for speciation analysis of chromium in natural water samples has been developed. Ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) were used as complexing agents for Cr(III) present in the sample and formed as products of Cr(VI) reduction, respectively. Under optimum experimental conditions linear relations in the range from 1×10^?6 to 3×10^?5 mol L^?1 without accumulation and from 1×10^?9 to 1×10^?7 at 30 s accumulation time were obtained for Cr(III) and Cr(VI), respectively. For samples in which Cr(III) concentration is higher than 1×10^?6 mol L^?1 the Cr(III) and Cr(VI) were determined simultaneously in one voltammetric cell. For samples in which Cr(III) concentration is below 1×10^?6 mol L^?1 only Cr(VI) was selectively determined in the presence of Cr(III), which did not influence the Cr(VI) signal. The determination of Cr(III) and Cr(VI) was successful with the application of the proposed procedure in the presence of common foreign ions. The presented method was applied for the speciation of chromium in spiked tap and river water samples with satisfactory results.     

Determination of Baicalin by High Performance Liquid Chromatography Coupling with Flow Injection Chemiluminescence Detection

A new method for the determination of baicalin in Scutellariae Radix extract and its preparations by high performance liquid chromatography (HPLC) coupling with flow injection chemiluminescence detection (FIA‐CL) has been developed. The method was based on the chemiluminescence reaction of potassium permanganate with baicalin in nitric acid medium; the CL intensity can be enhanced by formaldehyde. In this study, the conditions of chemiluminescence and chromatography were examined, and the schematic diagram of the HPLC‐FIA‐CL analyzer was optimized. The analytes were separated on Hypersil RP‐C18 columns (100 × 4.6 mm, I.D., 5 μm) by equality elution with 47:53 (v/v) methanol‐0.3% phosphoric acid as a mobile phase at a flow rate of 0.8 mL·min^?1 and a column temperature of 40 °C. Under the optimum condition, the CL intensity was proportional to the concentration of baicalin over the range of 4.10 × 10^?7 ? 6.15 × 10^?5mol·L^?1. The limit of detection (S/N = 3) was 2.79 × 10^?7mol·L^?1 with the relative standard deviation 2.5% (Cs = 6.15 × 10^?6 mol·L^?1, n = 5). The method has been applied to the determination of baicalin in Scutellariae Radix extract and its preparations, and satisfactory results were obtained.     

Catalytic Adsorptive Stripping Voltammetric Procedure for Determination of Total Chromium in Environmental Materials

A sensitive catalytic adsorptive stripping voltammetric procedure for determination of traces of total chromium in environmental samples is reported. The method is based on the preconcentration of a Cr(III)? H₂DTPA complex by adsorption at the HMDE from an acetate buffer solution at the potential ?1.0 V vs. Ag/AgCl. Total chromium was determined as Cr(III) after reduction of Cr(VI) to Cr(III) by NaHSO₃. In order to stabilize the signal of Cr(III) the measurements were performed at 5 °C. The calibration graph for chromium for an accumulation time of 60 s was linear in the range from 5×10^?10 to 5×10^?8 mol L^?1. The relative standard deviation for a chromium concentration of 1×10^?8 mol L^?1 was 3.9% (n=5). The detection limit for accumulation time of 60 s was about 8×10^?11 mol L^?1. The validation of the procedure was performed by the analysis of the certified reference materials.     

银（III）配合物-鲁米诺流动注射化学发光新体系测定肾上腺素

儿茶酚胺是一类非常重要的神经递质,在人体的心血管系统、神经系统、内分泌腺、肾脏、平滑肌等组织系统的生理活动中起着广泛的调节作用。肾上腺素为儿茶酚胺的一种,建立灵敏、高效的肾上腺素检测技术具有重要的临床意义。本文将银（Ⅲ）配合物与鲁米诺组成新的流动注射化学发光体系,利用碱性介质中肾上腺素对三价银配合物－鲁米诺化学发光体系有明显的增强效应来测定肾上腺素的含量,并据此建立了高效测定肾上腺素的流动注射化学发光新方法。在优化的条件下,该方法测定肾上腺素的线型范围为1.0×10－9～1.0×10－7 mol L-1,检出限为8.0×10－10 mol L-1,对1.5×10－8 mol L-1肾上腺素11次平行测定,其相对标偏差为2.9％。利用建立的分析方法测定了药物肾上腺素,并对三价银－鲁米诺化学发光新体系测定肾上腺素的反应机理进行了讨论。     

Determination of Total Chromium in Biological Samples by Automated Reagent Injection Chemiluminescence Analysis

A sensitive method for the determination of total chromium in real samples by flow injection–chemiluminescence (FI–CL) analysis was proposed. It was found that the CL intensity from luminol–lysozyme reaction could be markedly quenched, and the decrease of CL intensity was linear with the logarithm of Cr(III) concentrations over the range of 5.0 to 4000 pg mL^?1 with a detection limit of 2.0 pg mL^?1 (3σ) and relative standard deviations (RSDs) of 3.0, 2.6, and 2.0% for 10, 100, and 1000 pg mL^?1 Cr(III) (n = 7), respectively. At a flow rate of 2.0 mL min^?1, the whole process including sampling and washing could be accomplished within 36 s. The proposed CL method was successfully applied to the determination of total chromium in pharmaceutical capsules, a dietary supplement, and spiked human serum samples, with recoveries from 92.2 to 108.4% and RSDs of less than 4.0%. Using the homemade FI–CL model, the binding constant (K = 4.38 × 10⁶ L mol^?1) and the binding sites (n ≈ 1) of Cr(III) to lysozyme were given.     

Determination of Cr(VI) by Catalytic Adsorptive Stripping Voltammetry with Application of Nitrilotriacetic Acid as a Masking Agent

A selective and sensitive method for determination of traces of Cr(VI) in the presence of a large excess of Cr(III) by differential pulse catalytic adsorptive stripping voltammetry is presented. For minimization of Cr(III) interference nitrilotriacetic acid was used as a masking agent. The determinations were performed in a flow system. The calibration plot was linear from 1×10⁻¹⁰ to 1×10⁻⁸ mol L⁻¹ for accumulation time 60 s. The relative standard deviation for 3×10⁻⁹ mol L⁻¹ Cr(VI) was 4.1% (n=5). The detection limit for an accumulation time of 60 s was 4×10⁻¹¹ mol L⁻¹. The influence of common foreign ions is also presented. The performance of the method was verified by analysis of certified reference material for Cr(VI) and comparing the results of analyses of natural water samples with those obtained by another accepted electrochemical method.     

Automated Sequential‐injection Chemiluminescence Determination of Glucosamine Sulphate via Luminol‐Hydrogen Peroxide System

A highly sensitive automated sequential‐injection chemiluminescence (SIA‐CL) method for determination of glucosamine sulphate (GLS) was developed. The goal of the present work is the evaluation of the enhancement effect of the investigated drug glucosamine sulphate on the chemiluminescence reaction between luminol and H₂O₂ in alkaline medium of 1.0 × 10^?2 mol L^?1 sodium hydroxide at pH 11. The experimental conditions affecting the CL reaction such as the sequence of the reagents, concentrations, flow rate and aspirated volumes of reactants were systematically investigated and optimized. Under optimum conditions 50 μL of 1.0 × 10^?3 mol L^?1 luminol, 30 μL of a GLS test solution and 50 μL of 1.0 × 10^?2 mol L^?1 H₂O₂ were used and the luminescing zone was pushed into the detector at a flow rate 100 μL s^?1. The proposed method recorded high sensitivity, accuracy and simplicity that could be clarified as linear concentration range 1.0‐2000 ng mL^?1 with rectilinear part (r = 0.9992, n = 9) and limit of detection 0.3 ng mL^?1, along with relative standard deviation 1.3%. It was found that the developed method can be used directly to determine the investigated drug GLS in its pharmaceutical dosage forms and in spiked serum and urine by diluting the samples for a 1000 fold. The obtained results were statistically analyzed and compared with those obtained by the reported method.     

Spectrophotometric determination of Chromium(VI) using cyclam as a reagent

A simple, rapid, sensitive, and inexpensive method for spectrophotometric determination of chromium(VI), based on the absorbance of its complex with 1,4,8,11-tetraazacyclotetradecane (cyclam) is presented. The complex showed a molar absorbtivity of 1.5?×?10⁴?L?mol^?1?cm^?1 at 379?nm. Under optimum experimental conditions, a pH of 4.5 and 1.960?×?10³?mg?L^?1 cyclam were selected, and all measurements were performed 10?min after mixing. Major cations and anions did not show any interference; Beer's law was applicable in the concentration range 0.2–20?mg?L^?1 with a detection limit of 0.001?mg?L^?1. The standard deviation in the determination is ±0.5?mg?L^?1 for a 15.0?mg?L^?1 solution (n?=?7). The described method provides a simple and reliable means for determination of Cr(VI) in real samples.     

Flow Injection Chemiluminescence Determination of Puerarin in Pharmaceutical Preparations Using Eosin Y‐Fenton System

A novel chemiluminescence (CL) system was established for the determination of puerarin in pharmaceutical preparations. It was shown that a strong CL signal was observed when Eosin Y reacted with the hydroxyl radicals which were generated from Fenton reagent in acidic medium. The CL intensity was decreased significantly when puerarin was added to the reaction system and partially scavenged the hydroxyl radicals in the solution. The extent of decrease in the CL intensity had a good stoichiometrical relationship with puerarin concentration. Based on this, a new method for the determination of puerarin using a flow injection chemiluminescence technique was developed. The experimental parameters that affected the CL intensity were optimized. Under the optimal conditions, the linear range for puerarin concentration was 8.0×10^?8?2.0×10^?6 mol/L (R=0.9982) with a detection limit of 7.5×10^?9 mol/L (S/N=3) and the relative standard deviation was 1.7% for 4.0×10^?7 mol/L puerarin (n=11). The proposed method was applied to the determination of puerarin in a puerarin injection with satisfactory results.     

Determination of Melatonin in Rat Pineal Gland and Drug with Flow-Injection Chemiluminescence

A flow-injection chemiluminescence （CL） method for the determination of melatonin based on the CL reaction of melatonin with hydrogen peroxide and sodium hypochlorite （NaOCl） in a basic alkaline solution was developed. The possible CL mechanism has been discussed, and a proposal for the reaction pathway was given that singlet oxygen was clarified to be produced in this reaction system and was responsible for the CL emission. Under the optimized conditions, the linear concentration range of application was 1.0×10^-7-2.5 × 10^-4 moloL-I with a de- tection limit of 5.0 ×10^-8 moloL-1 （S/N= 3）. The relative standard deviation for eight repeated measurements of 1.0×10^-6 mol·L^-1 melatonin was 2.8%. The interferences of several important biological substances, some indole compound, cations and anions were studied. No interference was found for the anions, glucose, starch, most of cations and low concentration （less than 3.0 × 10^-6 mol·L^-1） of some biological substances and indole compound. The method was applied to the determination of melatonin in rat pineal gland and drug with satisfactory results. The sample throughput was 90 injections per hour.     

Ultraselective and Sensitive Determination of Cr(VI) in the Presence of a High Excess of Cr(III) in Natural Waters with a Complicated Matrix

In the present work, the catalytic adsorptive stripping voltammetric procedure for trace determination of Cr(VI) in the presence of a high excess of Cr(III) in natural waters with a complicated matrix has been developed. The influence from potentially interfering substances such as organic matter was successfully eliminated by exploiting adsorptive properties of polymeric resin. The detection limit estimated from 3 times the standard deviation for a low Cr(VI) concentration in the simultaneous presence of a 2×10³ fold excess of Cr(III), 50 mg L^?1 surfactants, 50 mg L^?1 humic substances and the accumulation time of 30 s was about 5.3×10^?10 mol L^?1.     

Determination of Diammonium Glycyrrhizinate and Its Antioxidant Activity Using a Novel Chemiluminescence System

A novel chemiluminescence (CL) system was established for the determination of diammonium glycyrrhizinate (DG) in pharmaceutical preparations and its ability of scavenging hydroxyl radical. It was shown that a strong CL signal was observed when Eosin Y mixed with Fenton reagent. The CL intensity was decreased significantly when DG was added to the reaction system and partially scavenged the hydroxyl radicals in the solution. The extent of decrease in the CL intensity had a good stoichiometrical relationship with DG concentration. Based on this, we developed a new method for the determination of DG using a flow injection chemiluminescence (FI-CL) technique. Under the optimal conditions, the linear range of DG concentration was 6.0 × 10^?8–5.0 × 10^?6 mol/L (R = 0.9982) with a detection limit of 8.0 × 10^?9 mol/L (SN = 3), and the RSD was 3.8% for 2.0 × 10^?7 mol/L DG (n = 11). This method was successfully used in the determination of DG in tablets and the evaluation of hydroxyl radical scavenging capacity of DG. The possible reaction mechanism of the CL system is discussed.     

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.     

Determination of Genistein by Flow‐injection Chemiluminescence Method Based on Ferricyanide Oxidation Sensitized by Rhodamine 6G

A novel flow injection chemiluminescence (FI‐CL) method for the determination of genistein was described. The method was based on the reaction between genistein and potassium ferricyanide in alkaline solution to give weak CL signal, which was dramatically enhanced by rhodamine 6G (Rh G). The CL emission allowed quantitation of genistein concentration in the range 1.0 × 10^?7–4.0 × 10^?5 mol/L with a detection limit (3σ) of 4.2 × 10^?8 mol/L. The relative standard deviation for 11 parallel measurements of 5.0 × 10^?7 mol/L, 4.0 × 10^?6 mol/L and 1.0 × 10^?5 mol/L genistein were 2.59%, 2.40% and 1.48%, respectively. The experimental conditions for the CL reaction were optimized and the possible reaction mechanism was discussed. The method was applied to the determination of genistein in biological fluids.     

Voltammetry of Dissolved Iron(III)–Nitrilotriacetate–Hydroxide System in Water Solution

The investigation of the dissolved iron(III)–nitrilotriacetate–hydroxide system in the water solution (I=0.1 mol L^?1 in NaClO₄; pH 8.0±0.1) using differential pulse cathodic voltammetry, cyclic voltammetry, and sampled direct current (DC) polarography, was carried out on a static mercury drop electrode (SMDE). The dissolved iron(III) ion concentrations varied from 2.68×10^?6 to 6×10^?4 mol L^?1 and nitrilotriacetate concentrations were 1×10^?4 and 5×10^?4 mol L^?1. By deconvoluting of the overlapped reduction voltammetric peaks using Fourier transformation, four relatively stable, dissolved iron(III) complex species were characterized, as follows: [Fe(NTA)₂]^3?, mixed ligand complexes [FeOHNTA]^? and [Fe(OH)₂NTA]^2?, showing a one‐electron quasireversible reduction, and binuclear diiron(III) complex [NTAFeOFeNTA]^2?, detected above 4×10^?4 mol L^?1 of the added iron(III) ions, showing a one‐electron irreversible reduction character. The calculations with the constants from the literature were done and compared with the potential shifts of the voltammetric peaks. Fitting was obtained by changing the following literature constants: log β₂([Fe(NTA)₂]^3?) from 24 to 27.2, log β₁([FeNTA]^?) from 8.9 to 9.2, log β₂([Fe(NTA)₂]^4?) from 11.89 to 15.7 and log β₂([Fe(OH)₂NTA]^3?) from 15.63 to 19. The determination of the electrochemical parameters of the mixed ligand complex [FeOHNTA]^?, such as: transfer coefficient (α), rate constant (k_s) and formal potential (E°') was done using a sampled DC polarography, and found to be 0.46±0.05, 1.0±0.3×10^?3 cm s^?1, and ?0.154±0.010 V, respectively. Although known previously in the literature, these four species have now for the first time been recorded simultaneously, i.e. proved to exist simultaneously under the given conditions.     

Development and application of the tartrazine voltammetric sensors based on molecularly imprinted polymers

A modified glassy carbon electrode was prepared as an electrochemical voltammetric sensor based on molecularly imprinted polymer film for tartrazine (TT) detection. The sensitive film was prepared by copolymerization of tartrazine and acrylamide on the carbon nanotube-modified glassy carbon electrode. The performance of the imprinted sensor was investigated by cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy in detail. Under the optimum conditions, two dynamic linear ranges of 8?×?10^?8 to 1?×?10^?6?mol?L^?1 and 1?×?10^?6 to 1?×?10^?5?mol?L^?1 were obtained, with a detection limit of 2.74?×?10^?8?mol?L^?1(S/N?=?3). This sensor was used successfully for tartrazine determination in beverages.     

Separation and spectrophotometric determination of very low levels of Cr(VI) in water samples by novel pyridine-functionalized mesoporous silica

A modified SBA-15 mesoporous silica was developed, as an adsorbent, for the removal of Cr(VI) ions from natural-water samples. The effects of experimental parameters, including pH of solution, sample and eluent flow rate, the eluent composition, the eluent volume, and the effect of coexisting ions on the separation and determination of Cr(VI), were investigated. It was shown that Cr(VI) was selectively adsorbed from aqueous solution at pH 3, but Cr(III) could be adsorbed from solution at alkaline pH range. The retained Cr(VI) was eluted with 0.5?mol?L^?1 KCl solution in 0.1?mol?L^?1 Na₂CO₃ subsequently. Under the optimum conditions, the modified mesoporous silica (py-SBA-15) with a high pore diameter exhibited an adsorption capacity of 136?mg?g^?1 and a lower limit of detection than 2.3?µg?L^?1 by using diphenylcarbazide as a chromophorous reagent for the determination of Cr(VI) ions. A preconcentration factor as high as 200 was calculated for Cr(VI). The loaded py-SBA-15 can be reactivated with recovery of more than 98.5% over at least eight cycles. The relative standard deviation (RSD) for Cr(VI) ion recovery was less than 1.8%. Validation of the outlined method was performed by analysing a certified reference material (BCR 544). The proposed method was applied to determine Cr(VI) value in natural and waste water samples successfully.