Determination of Nickel in Fuel Ethanol Using a Carbon Paste Modified Electrode Containing Dimethylglyoxime

A mercury-free electrode chemically modified with carbon paste containing dimethylglyoxime was used for determination of nickel in fuel ethanol. The instrumental parameters and composition of the modified paste were optimized. The analytical curve for nickel determination from 5.0 × 10⁻⁹ to 5.0 × 10⁻⁷ mol L⁻¹ was obtained using 25 min of accumulation time. The detection limit and amperometric sensitivity obtained for this method were 2.7 × 10⁻⁹ mol L⁻¹ and 5.2 × 10⁸ μA mol⁻¹ L, respectively. The values for nickel concentration in four commercial samples of fuel ethanol were obtained in the range of 1.1 × 10⁻⁸ to 6.9 × 10⁻⁸ mol L⁻¹. A comparison to graphite furnace atomic absorption spectrometry (GFAAS) was performed for nickel determination in commercial samples of ethanol.     

[Cr(III)(SSA)(en)2]•2H2O配合物的合成、表征及性质研究

有机铬(III)配合物具有较高的生物利用率. 本文合成了一种新型磺基水杨酸铬(III)混配配合物[Cr(SSA)(en)₂]•2H₂O (SSA＝5-磺基水杨酸, en＝乙二胺), 通过红外、紫外、荧光光谱以及元素分析、电导率测定和X晶体衍射等方法对其结构进行了表征. 在pH 7.4, 0.05 mol•L^－1 Tris-HCl缓冲液中, 利用荧光光谱研究了配合物与人血清白蛋白的结合. 结果表明配合物可与人血清白蛋白以较强的分子间作用力结合, 条件结合常数为(2.7±0.1)×10⁴ mol•L^－1, 结合位点数为3.87. 在pH 7.4, 0.05 mol•L^－1 Tris-HCl缓冲液中, 观察了不同温度下EDTA和脱铁伴清蛋白为竞争剂的配体取代反应动力学行为, 其中37 ℃时反应速率常数分别为0.0142和0.0225 h^－1.     

Rapid, sensitive and selective spectrophotometric determination of phosphate as an ion associate of 12-molybdophosphate with Astra Phloxine

A highly sensitive and selective reaction of 12-molybdophosphate with the polymethine dye Astra Phloxine has been used for the spectrophotometric determination of phosphate. If the concentration of phosphate is less than 1 μmol L⁻¹, supersaturated solutions of ion associate (IA) are stable without the use of a surfactant. Under these conditions, a new band appears in the absorption spectrum at 574 nm. The color of the IA develops immediately after mixing of reagents and remains constant over several hours. The molar absorptivity of the IA is 1.54 × 10⁵ L mol⁻¹ cm⁻¹. The calibration graph is linear between 0.02 and 0.8 μmol L⁻¹ of phosphate. The limit of detection is 7 nmol L⁻¹. Phosphate was determined in pure chemicals and water samples, including Dead Sea water.     

Immobilization of Hexacyanoferrate on a Gold Self-Assembled Monolayer, and its Application as a Sensor for Ascorbic Acid

Hexacyanoferrate (II/III) (HCF) was immobilized on a gold electrode modified with cysteamine (CSTE). The Au/CSTE/HCF/PLL electrode was prepared with layer-by-layer (LBL) technique with HCF and poly-d-lysine (PLL). The Au/CSTE/HCF/PLL electrode presented the electrocatalytic activity for ascorbic acid oxidation. The maximum electrocatalytic current was reached at 0.28 V vs SCE in 0.01 mol L⁻¹ TRIS buffer, at pH 7.0. The Au/CSTE/HCF/PLL electrode response was stable under various oxidation–reduction cycles in TRIS medium, showing that the system is very stable. The solution pH has no effect on the anodic peak potential and anodic peak current in the range from 4 up to 10. The intensity of the anodic peak current varied with the concentration of ascorbic acid from 1 up to 910 μmol L⁻¹, with a sensitivity of 62.9 nA cm⁻² L μmol⁻¹, a detection limit of 0.65 μmol L⁻¹ and a quantification limit of 2.2 μmol L⁻¹. The developed sensor was successfully applied for ascorbic acid determination in pharmaceutical samples. The results compared to those obtained with a reference method were statistically the same with 95% of confidence level.     

A novel kinetic determination of nitrite based on the perphenazine-bromate redox reaction

An extremely sensitive and selective kinetic method was developed for the determination of trace levels of nitrite based on its catalytic effect on the oxidation of perphenazine (PPZ) with bromate in a phosphoric acid medium. The reaction rate was monitored spectrophotometrically by tracing the formation of the red-colored oxidized product of PPZ at 525 nm within 30 sec of mixing. The optimum reaction conditions were 4.0 μmol L⁻¹ PPZ, 0.4 mol L⁻¹ H₃PO₄ and 30 mmol L⁻¹ bromate at 25 °C. Using the recommended procedure, nitrite could be determined with a linear calibration graph up to 4.50 ng mL⁻¹ and a detection limit of 0.07 ng mL⁻¹. The method was conveniently applied to the determination of nitrite in samples of rain, polluted well and formulated waste waters. Moreover, the published kinetic spectrophotometric methods for nitrite determination are reviewed.     

Electrochemical determination of malachite green using a multi-wall carbon nanotube modified glassy carbon electrode

A multi-wall carbon nanotube (MWNT) film-modified electrode is described for the determination of malachite green (MG). The electrochemical profile of MG was examined using cyclic voltammetry (CV) and differential pulse voltammetry (DPV), suggesting that the MWNT film facilitates the electron transfer of MG in terms of a potential shift and then significantly enhances the oxidation peak current of MG. The experimental parameters, such as supporting electrolyte, thickness of MWNT film, scan rate and accumulation time, were optimized. Consequently, a sensitive and convenient electrochemical method is proposed for the determination of MG. The oxidation peak current is proportional to the concentration of MG over the range from 5.0 × 10⁻⁸ to 8.0 × 10⁻⁶ mol L⁻¹ obeying the following equation: i_p = 0.09 + 1.19 × 10⁷ C (r = 0.995, i_p in μA, C in mol L⁻¹). The detection limit is 6.0 × 10⁻⁹ mol L⁻¹ (signal to noise = 3) after 5 min of accumulation. Moreover, this method possesses good reproducibility (RSD is 5.6%, n = 8) as well as long-term stability. Finally, the new method was employed to determine MG in fish samples. Correspondence: W. Huang, Department of Chemistry, Hubei Institute for Nationalities, Enshi 445000, P.R. China     

Chemiluminescence method for the determination of mitoxantrone by the enhancement of the tris-(4,7-diphenyl-1,10-phenanthrolinedisulfonic acid)ruthenium(II)–cerium(IV) system

2,5-Dimercapto-1,3,4-thiadiazole (DMTD) self-assembled monolayer on gold electrode was prepared and investigated by electrochemical measurement. The DMTD/Au electrode exhibited a significantly increased sensitivity and selectivity for Pb(II) in acetate buffer (pH 5.5) at a potential of −1.0 V (vs Ag/AgCl) for 4 min by anodic stripping voltammetry. The influence of various experimental parameters on the voltammetric response was studied. Under the optimized working conditions, the dependence of the stripping peak current response on concentration of Pb(II) was linear in the range of 1–45 μmol L⁻¹ with a correlation coefficient of 0.9988, and the detection limit was 0.10 μmol L⁻¹. The relative standard deviation of the results was 3.4% for six successive determinations of a 20 μmol L⁻¹ Pb(II) solution. A study of interfering substances was also performed. The method was applied to the determination of Pb(II) in water samples with satisfactory results. Correspondence: Hong Qun Luo, School of Chemistry and Chemical Engineering, Southwest University, 400715 Chongqing, China     

Fluorometric determination of DNA using nano-SiO2 particles as an effective dispersant and stabilizer for acridine orange

A sensitive fluorometric method for the determination of ctDNA (calf thymus DNA) is presented. It has good selectivity and sensitivity and uses nano-SiO₂ particles as an effective dispersant and stabilizer for acridine orange (AO). Compared to resonance light scattering (RLS) and the conventional method that uses organic dyes as fluorescence probe, the new method is more tolerant towards coexisting foreign substances and also more stable. With 20 mg nano-SiO₂ particles, 10 μmol L⁻¹ AO, at pH 8.01 and an ionic strength of 0.02 mol L⁻¹, the interaction of AO with nano-SiO₂ and ctDNA results in fluorescent signal enhancement. The extent of enhancement was in good proportion to the concentration of ctDNA at excitation/emission wavelengths of 490/523 nm, respectively. The calibration curve was linear over 0.66–55.60 μg mL⁻¹. The determination limit (3σ) was 15 μg mL⁻¹. The method was applied to the determination of ctDNA in synthetic samples with satisfactory results.     

Cloud point extraction procedure for flame atomic absorption spectrometric determination of lead(II) in sediment and water samples

The conditions for cloud point extraction of lead(II) from aqueous solutions were investigated and optimized. The procedure is based on the separation of Pb(II) – brillant cresyl blue (BCB) complexes into the micellar media by adding the surfactant Triton X-114. After phase separation, the surfactant-rich phase was dissolved with 1 mol L⁻¹ HNO₃ in ethanol and diluted with 1 mol L⁻¹ HNO₃ solution before lead was determined by flame atomic absorption spectrometry. Optimization of the pH, ligand and surfactant quantities, incubation time, temperature, viscosity, sample volume, and interfering ions was performed. The effects of the matrix ions were also examined. The detection limits for three times the standard deviations of the blank for lead were 7.5 μg L⁻¹ for water samples and 0.33 μg g⁻¹ for sediment samples. The validity of cloud point extraction was checked by employing certified reference samples of Lake Sediment IAEA-SL-1 and Sewage Sludge BCR-CRM 144R. The procedure was applied to natural waters and sediment samples with satisfactory results (recoveries >95%, relative standard deviations <6.4%).     

Indirect determination of free cyanide in water and industrial waste water by flow injection-atomic absorption spectrometry

A simple and rapid flow injection system is proposed for indirect determination of cyanide by flame atomic absorption spectrometry. It consists of a microcolumn of immobilized salen (N,N′-bis(salicylidene)ethylenediamine) on sodium dodecyl sulfate (SDS)-coated alumina saturated with silver ion and a carrier of dilute solution of sodium hydroxide (10⁻⁵ mol L⁻¹). The micro-column was located between the injection valve and nebulizer of atomic absorption spectrometry. Injection of 250 μL of aqueous cyanide standard or sample solution at pH range of 9–11 cause elution of silver as silver cyanide complexes, which was then measured by flame atomic absorption spectrometry. The absorbance was proportional to the concentration of cyanide in the sample. The graph of absorbance (as peak height) vs. cyanide concentration was linear over the concentration range of 0.1–10 mg L⁻¹ of cyanide, and the detection limit was 0.06 mg L⁻¹. The relative standard deviation at 1 and 3 mg L⁻¹ of cyanide concentration were 4.1 and 4.7%, respectively. The method was successfully applied to determination of cyanide in water and industrial waste waters, and the accuracy was examined through independent analysis by accepted method of pyridine-barbituric acid.     

Online preconcentration system for determining ultratrace amounts of Cd in vegetal samples using thermospray flame furnace atomic absorption spectrometry

A system has been developed for online preconcentration and determination of Cd using thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS). It is based on the solid-phase extraction of Cd in an Amberlite XAD-2 minicolumn loaded with 2-(2-thiazolylazo)-5-dimethylaminophenol (TAM), and the metal ion is eluted with 1 mol L⁻¹ hydrochloridric acid, followed by its determination. The online system allows determining Cd with a detection limit of 8.0 ng L⁻¹ and a quantification limit of 25.0 ng L⁻¹. The precision (repeatability), calculated as the relative standard deviation (% RSD) in sample solutions containing 0.5 and 3.0 μg L⁻¹ of Cd, was 6.1 and 4.5%, respectively. The preconcentration factor obtained was 24. The system’s accuracy was confirmed by analyzing the following certified reference materials (CRMs): Rice flour NIES 10b, Apple leaves NIST 1515 and Orchard leaves NBS 1571. This procedure was applied to the determination of Cd in cabbage and powdered guarana samples.     

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     

H2O2-鲁米诺-荧光素钠-K2CO3高灵敏化学发光法测定二氧化碳

在碱性介质中, CO₃^2－对H₂O₂氧化鲁米诺化学发光反应具有重要作用, 荧光素钠对该反应具有很强的增敏作用. 据此, 建立了化学发光法测定二氧化碳的新方法. 方法的线性范围为1.0×10^－10～5.0×10^－6 mol•L^－1 CO₃^2－, 检出限为 1.2×10^－11 mol•L^－1 CO₃^2－ (相当于5.3×10^－10 g•L^－1 CO₂). 该方法用于室内外空气中二氧化碳含量的测定, 相对标准偏差1.8%～2.1% (n＝11), 加标实验回收率97.6%～101.4%. 论文还探讨了反应的发光机理, 发光反应很可能是由溶液中的CO₃^2－与H₂O₂作用而产生的活性自由基引发, 荧光素钠对发光的增敏作用为化学能量转移过程.     

Application of Nb2O5–SiO2 in Pre-Concentration and Determination of Copper and Cadmium by Flow System with Flame Atomic Absorption Spectrometry

 The use of niobium (V) oxide, chemically adsorbed on silica gel surface (Nb₂O₅–SiO₂), as an adsorbent in a pre-concentration system for copper (II) and cadmium (II) determination was proposed. The procedure is based on the large ion-exchange capacity for the adsorption of copper (II) and cadmium (II) ions on the mini-column packed with Nb₂O₅–SiO₂, followed by elution with 2.0 mol L⁻¹ nitric acid and determination by flame atomic absorption spectrometry. Chemical and flow variables were optimized. The results demonstrated that the sample solutions containing copper (II) or cadmium (II) in a concentration range of 3.0 to 600.0 μg L⁻¹ and 3.1 to 100.0 μg L⁻¹ respectively, in a solution of pH 5.0 could be determined using a pre-concentration time of 2 min. The enrichment factor when using a sample volume of 10.2 mL and 2 min of pre-concentration was 17.5 and 20.3 for copper (II) and cadmium (II), respectively. The limit of detection for copper (II) and cadmium (II) was 0.5 μg L⁻¹ and 1.0 μg L⁻¹, respectively. The relative standard deviation (RSD) was lower than 1.4% for copper (II) and cadmium (II) when using a concentration of 25.0 μg L⁻¹ for both metals. The method was tolerant to other ions usually present in water samples. Good accuracy was obtained by the analysis of water reference material and environment samples. Correspondence: Universidade Federal de Santa Catarina, Departamento de Química, Florianópolis SC, Brazil. e-mail: carasek@qmc.ufsc.br Received July 16, 2002; accepted October 25, 2002     

一种基于壳聚糖固定葡萄糖氧化酶的葡萄糖生物传感器的研究

本文选用生物相容性好的壳聚糖作为基体材料，使其与戊二醛交联成网状结构包埋葡萄糖氧化酶制成电化学传感器。这种壳聚糖膜不仅可以减小葡萄糖氧化酶的流失，而且能为酶提供了适宜的微环境。用红外光谱、紫外光谱及透射电镜对膜的形态和性质进行了表征。实验结果表明该传感器具有很快的响应速度，很好的稳定性和重现性，能选择性地催化葡萄糖并测定其浓度。该传感器的制备方法简单，成本低，于冰箱中放置两周信号保持在90％以上，对葡萄糖测量的线性范围为1×10^-5 - 3.4×10^-3mol•L^-1，当信噪比为3:1时检测限为5×10^-6mol•L^-1。     

Microdialysis sampling and chemiluminescence detection for in vivo and real-time study of the lead metabolism in rabbit blood

The chemiluminescence (CL) system K₂MnO₄-luminol is shown to be useful for the determination of lead(II). The method is based on the catalytic effect of Pb(II) on the CL reaction. The linear range was 3 × 10⁻³–9 × 10⁻¹ mg L⁻¹ (r = 0.9971) and the relative standard deviation (R.S.D.) for 5 × 10⁻² mg L⁻¹ Pb(II) measurement was 0.7% (n = 11). The detection limit was 3 × 10⁻⁴ mg L⁻¹ (3σ) Pb(II). Based on this, an in vivo, on-line, real-time analytical system for monitoring the metabolism of free lead(II) in rabbit blood was developed. A microdialysis probe, implanted in the vein of a rabbit, was perfused with perfusate at a flow rate of 5 μL min⁻¹. The concentration of free lead(II) in the dialysate was determined on-line with a flow-injection CL system. This system included microdialysis sampling, on-line separation and chemiluminescence detection. The concentration-time curve of lead(II) was in accordance with the one-compartmental open model, T_1/2 (elimination half-life), T_max (peak time) and C_max (peak concentration) were 37.77 min, 85.20 min and 0.137 mg L⁻¹, respectively.     

Spectrofluorimetric Determination of Cu2＋ Using New Fluorogenic Reagent

A new synthesized fluorogenic reagent,8-[(2-pyridine)methylideneamino] quinoline (PMAQ), was utilized for spectrofluorimetric determination of Cu(II) at trace levels. PMAQ, a good fluorogenic reagent, though insoluble in water, but is soluble in ethanol and 20% ethanol-water. The excitation and the fluorescence wavelengths of PMAQ were 310 and 434 nm respectively. When the reagent was complexed with Cu(II), the fluorescence intensity decreased proportionally with the concentration of Cu(II) at pH 4.5 by a static quenching effect. The highest sensitivity to Cu^2＋ determination was shown to be at PMAQ concentration of 1.0×10^－5mol•L^－1. In order to enhance the quenching effect, the Cu(II)-PMAQ complex solution was kept at 22 ℃ for 20 min. Though the interferences by Co(II) and Fe(III) were very serious, they were however, completely eliminated by being masked with oxalate and ascorbate ions respectively. The linear dynamic range for Cu(II) determination was between 25—441 µg•L^－1 with the detection limit of 18 µg•L^－1 (RSD＝3.7%, n＝6). The proposed method was successfully applied to the determination of Cu(II) in real samples including human blood serum, commercial tea and wheat flour.     

Studies on the Efficiency of Hydrogen Selenide Generation with Different Acid Media by Continuous Flow Hydride Generation Atomic Absorption Spectrometry

The efficiency of hydrogen selenide generation by HCl, HBr, H₂SO₄, HClO₄ and HNO₃ was studied with varying NaBH₄ concentrations by continuous flow hydride generation AAS. HBr showed higher efficiency (≈20%) than the conventionally used HCl. The optimum concentration of reagents were 5 M HBr, with 0.5% NaBH₄ and 6 M HCl with 1% NaBH₄. The efficiency followed the order HBr>HCl>HClO₄>H₂SO₄>HNO₃. The sensitivity and detection limits were 0.16 μg L⁻¹ and 0.15 μg L⁻¹ with HBr, and, 0.19 μg L⁻¹ and 0.17 μg L⁻¹ with HCl. The calibration graphs were linear in the range of 2–25 μg L⁻¹ for both the acids. Se⁶⁺ was reduced to Se⁴⁺ in 1 M HCl with the addition of solid KBr (4% final solution) with 60 minutes heating at 70 °C and compared to the commonly used 6 M HCl with 15 minutes boiling. Pre-reduction with KBr showed signal enhancement by 5 to 10% in the range 2–25 μg L⁻¹ of Se⁴⁺. The application of the method to SRM 1640 demonstrated that results were in good agreement with the certified values. Groundwater samples from a suburban area were analyzed and reported.     

基于Ru(bpy)32+-SiO2纳米颗粒的核酸适配体传感器对凝血酶的电致化学发光检测

本文应用核酸适配体构建了一种新型的电致化学发光检测蛋白体系。两个核酸适配体结合凝血酶的两个不同位点,利用这两核酸适配体与凝血酶的高亲和力构建三明治传感体系检测凝血酶。一个核酸适配体固定在金电极上用来捕获凝血酶,另一个标记有包裹电致化学发光活性物Ru(bpy)₃²⁺的二氧化硅纳米颗粒,用来检测电致化学发光信号。此核酸适配体传感器对凝血酶具有特异识别性,电致化学发光信号与凝血酶的浓度直接相关,非特异性识别的牛血红蛋白、牛血清白蛋白不干扰测定。由于在检测的核酸适配体上标记的纳米颗粒包裹有多个发光活性物,因此大大提高了发光效率和灵敏度,此法对凝血酶的线性响应范围为2.0 fmol•L^-1～2.0 pmol•L^-1,检测限可达1.0 fmol•L^-1。     

ApoCopC与汞（II）结合性质的光谱研究

在室温, pH 7.4, 10 mmol•L^-1Hepes（N-2-hydroxyethylpiperazine-N’-2-ethane-sulfonic acid）缓冲溶液条件下，通过紫外光谱法研究了apoCopC与汞（II）的结合性质。结果表明apoCopC的N，C- 端均可结合汞（II），且测得条件结合常数分别为K_n=(6.79 ± 1.12)´10⁶ mol^-1•L和K_c= (3.06±0.05)´10⁵ mol^-1•L。在pH 7.4，50 mmol·L^-1Hepes缓冲溶液条件下，用荧光光谱法研究了apoCopC的脲变性性质。结果表明汞（II）的结合对蛋白结构的维系具有稳定作用，并测得Hg_N²⁺-CoC-Hg_c²⁺ 和apoCopC的稳定吉布斯自由能（ΔG_D^H2O）分别为14.69±0.85 kJ•mol^-1和 16.66±0.55 kJ•mol^-1。