CATALYTIC KINETIC SPECTROPHOTOMETRIC DETERMINATION OF SODIUM DODECYL SULPHONATE

A novel catalytic kinetic spectrophotometric method for the determination of trace sodium dodecyl sulphonate (SDS) is proposed using the principle that trace SDS catalyses the oxidation fading reaction of rhodamine B by potassium periodate. Under the optimum reaction conditions, a good linear relationship is presented between the reaction rate and the mass concentration of SDS over the range of 0.30–1.0 μg/mL at its maximum absorption wavelength of 552 nm. The detection limit of the method was 0.152 μg/mL. The method has been successfully used to determine SDS in scour and water samples.     

CATALYTIC KINETIC SPECTROPHOTOMETRIC DETERMINATION OF TRACE AMOUNTS OF ETHYLENEDIAMINETETRAACETIC ACID BASED ON ITS CATALYTIC EFFECT ON THE REACTION OF RHODAMINE B AND POTASSIUM DICHROMATE

A new method for the determination of trace ethylenediaminetetraacetic acid (EDTA) was developed using catalytic kinetic spectrophotometry based on the principle that in the medium of 0.10 mol/L sulfuric acid, trace EDTA has a catalytic effect on the oxidation of rhodamine B by potassium dichromate, and a suitable amount of 6.0 mol/L NaOH solution can inhibit the catalytic reaction. At the maximum absorption wavelength of 546 nm, the linear range for the determination of EDTA was shown over the concentration range 5.0 × 10^?5–7.0 × 10^?4 mol/L and the detection limit of this method for EDTA was 0.0501 mmol/L. The linear regression equation for the determination of EDTA and regression coefficient were ΔA = 512C (C: mol/L) + 0.0966, γ = 0.9993, respectively. The apparent activation energy of the catalytic reaction was 81.57 KJ/mol. The proposed method has been successfully applied to the determination of trace ethylenediaminetetraacetic acid in water and apple tinned foodstuff samples with satisfactory results. The relative standard deviation of 13 replicate determinations of EDTA was 1.15–2.37% and the recovery of the method was 99.90–102.7%, respectively. The determined results were in good agreement with that of established method Fe(III)-H₂O₂-bromothymol blue system inhibitory-kinetic spectrophotometry.     

INHIBITIVE KINETIC SPECTROPHOTOMETRIC DETERMINATION OF PROTEIN

A novel inhibitive kinetic spectrophotometric method for the determination of protein is proposed based on the principle that serum albumin (SA) has an inhibitive effect on the oxidation discoloring of p-acetylchlorophosphonazo (CPApA) by potassium periodate in the medium of 4.0 × 10^?4 mol/L H₂SO₄ at 100°C. The maximum absorption peak of SA – CPApA – KIO₄ system is located at 550 nm. The absorbance difference (ΔA) is linearly related with the concentration of SA over the range of 0.80–7.50 µg/mL at the wavelength and fitted the equation: ΔA = 0.064C (C: µg/mL) – 0.0173, with a correlation coefficient γ = 0.9973. The detection limit of the method was 0.30 μg/mL. The method was successfully used to determine protein content in milk and milk powder samples and the determined results were in good agreement with those of tribromoarsenazo spectrophotometry. The relative standard deviation for 13 replicate determinations of the method was 3.64–3.76%. The standard addition recovery of the method was 99.50–101.6%.     

Characterization and application of lornoxicam,europium(III), and lysozyme fluorescence

A novel and sensitive spectrofluorimetric method was developed for the determination of lornoxicam. The method was based on the fluorescence enhancement of europium(III) by formation of a ternary complex with lornoxicam in the presence of lysozyme as the co-ligand. The fluorescence signal for the lornoxicam-europium (III)-lysozyme system was monitored at an excitation wavelength of 620 nm and an emission wavelength of 390 nm. The parameters affecting the fluorescence intensity were optimized systematically and under these conditions the signal was directly proportional to the concentration of lornoxicam from 9.0 × 10^?5 to 1.0 × 10^?2 µg · mL^?1. The detection limit was 2.7 × 10^?5 µg · mL^?1. The relative standard deviation for thirteen replicate measurements of 1.0 × 10^?3 µg · mL^?1 lornoxicam was 1.8%. This method was employed for the determination of lornoxicam in pharmaceutical formulations and biological fluids. The mechanism of fluorescence for the lornoxicam-europium(III)-lysozyme system was discussed.     

荧光光度法选择性测定水样中痕量镉的研究

本文研究了镉 (Ⅱ ) 8 羟基喹啉 5 磺酸 溴代十六烷基三甲胺体系测定痕量镉的荧光分析方法。Cd(Ⅱ )与 8 羟基喹啉 5 磺酸 (HQS)在强碱性条件下能选择性地形成稳定的配合物 ,发射较强的荧光 ,激发波长和发射波长分别位于 394nm和 5 2 0nm。在溴代十六烷基三甲胺 (CTMAB)表面活性剂存在时 ,络合物的荧光强度显著地增强。在碱性条件下 ,CTMAB浓度为 3× 1 0 3mol/L时 ,镉 (Ⅱ )的浓度在 4 3× 1 0 9～ 6 0× 1 0 6 mol/L范围内线性关系良好 ,检出限为 4 3nmol/L。应用本方法测定生活及环境水样后 ,共加标回收率为1 1 7 1 %～ 1 2 1 8%。本方法操作简便、选择性好、准确度高 ,可直接应用于水样品中镉含量的测定 ,结果令人满意     

Kinetic Spectrophotometric Determination of Traces of Iron by its Catalytic Effect on the Oxidation of m-Acetylchlorophosphonazo by Hydrogen Peroxide

Abstract

In the buffer medium of KHC₈H₄O₄–HCl at pH 3.2, a catalytic kinetic spectrophotometric method for the determination of iron was developed by use of the catalytic effect of iron(III) on the oxidation of m-acetylchlorophosphonazo by hydrogen peroxide. At the wavelength of 544 nm, the difference of absorbance(?A) is well linearly related with the concentration of iron(III) in the range of 0–2.5 µg/25 mL and fitted the equation: ?A = 0.1469 C(µg/25 mL) + 0.0037, with a regression coefficient of 0.9979.The detection limit of the method is 1.34 ng/mL. The present method was successfully applied to determine iron in rice samples.     

Resonance Rayleigh Scattering of K2Zn3[Fe(CN)6]2 Nanoparticles and its Application for the Determination of Vitamin C

Abstract

In Britton-Robinson buffer medium, (pH 4.43), potassium ferricyanide (K₃[Fe(CN)₆]) could react with vitamin C (VC) to produce potassium ferrocyanide (K₄[Fe(CN)₆]), which further reacted with Zn²⁺ to form potassium zinc hexacyanoferate K₂Zn₃[Fe(CN)₆]₂ nanoparticles. The shapes and diameters of the K₂Zn₃[Fe(CN)₆]₂ nanoparticles have been observed with transmission electron microscopy, which showed the shapes of these nanoparticles was cubic and their average sizes were about 50 nm in the presence of 2.0 × 10^?5 mol L^?1 VC. The characteristics of resonance Rayleigh scattering (RRS) spectra of this reaction have been studied. The optimum reaction condition for the determination of VC has been investigated. It was found that the RRS intensity of the system at the RRS peak of 363.4 nm was proportional to the VC concentration in the range of 4.0?80.0 µmol L^?1, and the detection limit (3σ) for VC was 0.075 µmol L^?1. A novel and simple RRS method for the determination of VC based on the formation of K₂Zn₃[Fe(CN)₆]₂ nanoparticles has been established.     

Effect on Particle Size to Emitted X-Ray Intensity in Pellet Cement Sample Analyzed with WDXRF Spectrometer

Abstract

The particle size and heterogeneity effects on the analyte line were investigated for the analysis of powdered samples by X-ray fluorescence technique. In the analysis of samples utilizing the powder method, these effects caused serious errors with variations in particle size for the emitted intensity. The fluorescence intensities of some elements in pellet samples of cement (the range of particle sizes, < 32 µm, 32–38 µm, 38–45 µm, 45–63 µm, 45–75 µm, 75–106 µm, and 106–150 µm and, at press pressure 3.50 and 1.41 × 10⁷ kg/m²), are measured using a wavelength dispersive X-ray fluorescence (WDXRF) spectrometer for 14 pellets prepared according to the powder method. The results show that the K _α X-ray fluorescence intensities from samples can effect about 17% maximum differences in normalized intensities within selected particle sizes. These experimental results were interpreted by comparing with the other experimental results in the literature.     

SENSITIVE L-CYSTEINE AMPEROMETRIC SENSOR BASED ON A GLASSY CARBON ELECTRODE MODIFIED BY MnO2 NANOPARTICLES

A sensitive amperometric sensor for the determination of L-cysteine was fabricated by electrodeposition of modified MnO₂ nanoparticles on a glassy carbon electrode. The morphology of the nanoparticles was characterized by scanning electron microscopy. Cyclic voltammetry was applied to investigate the mechanism of film formation and the electrochemical properties of the MnO₂ nanoparticle-modified electrode. The results of electrochemical experiments showed that the modified electrode had a favorable catalytic ability for the electrochemical oxidation of L-cysteine. Under optimized conditions, the MnO₂ nanoparticle-modified electrode exhibited a linear dependence on the concentration of L-cysteine from 1.0 × 10^?6 to 6.4 × 10^?4 M, and a detection limit of 8.0 × 10^?7 M (signal/noise = 3). The modified electrode was highly resistant towards typical inorganic salts and some biomolecules. In addition, the sensor was applied for the determination of L-cysteine in human serum with high accuracy, demonstrating its potential for practical applications.     

KINETIC SPECTROPHOTOMETRIC DETERMINATION OF TRACE AMOUNT OF EUROPIUM BASED ON ITS INHIBITORY EFFECT OF THE OXIDATION OF SWITZERLAND PIGMENT BY POTASSIUM BROMATE

In 4.0 × 10^?3 mol/L of hydrogen chloride medium, a trace of europium(III) plays a good inhibitory role in the fading reaction of Switzerland pigment oxidized by potassium bromate. Based on this principle, an inhibitory kinetic spectrophotometric method for the determination of trace europium was developed. A maximum absorption wavelength locates at 600 nm and a good linear range is presented over 0 – 0.18 µg/mL of europium(III) under the optimum conditions. The regression equation for the determination of europium(III) is ΔA = 4.495C(C:μg/mL) + 0.0278 with a correlation coefficient of 0.9965. The detection limit of the method was 19 ng/mL. The apparent activation energy of the inhibitory reaction and the reaction half-life period were 5.76 KJ/mol and 15.61 min, respectively. This method has been successfully used in the determination of europium in molecular sieve samples.     

Determination of phenolic acids and rutin in Heliotropium thermophilum by high-performance liquid chromatography with photodiode array detection

A novel and rapid method was validated for the determination of phenolics in plants by high-performance liquid chromatography coupled to photodiode array detection. The optimized method was employed for the quantification of phenolic acids and rutin present in Heliotropium thermophilum. Eight samples collected from two locations were analyzed. Additionally, temperature dependent changes in the phenolic composition of H. thermophilum samples was evaluated. A series of standards were used for identification that included gallic acid, protocatechuic acid, 4-hydroxybenzoic acid, chlorogenic acid, vanillic acid, caffeic acid, syringic acid, p-coumaric acid, rutin, ferulic acid, benzoic acid, 2-hydroxycinnamic acid, abscisic acid, and trans-cinnamic acid. Chromatographic separation was performed on C₈ column at 40°C with gradient elution. A phosphate buffer (20 mM, pH: 2.5) and acetonitrile mixture was used as the mobile phase with detection at 280 nm wavelength and a flow rate of 1.5 mL/min. The developed method was shown to be sensitive, accurate, and reproducible for the determination of phenolic acids and rutin in plants.     

DETERMINATION OF LEAD(II) BY FLOW-INJECTION ANALYSIS USING LUMINOL-POTASSIUM PERIODATE POST-CHEMILUMINESCENCE REACTION

The post-chemiluminescence (PCL) phenomenon arising from the potassium periodate–luminol reaction induced by lead(II) was investigated. A strong PCL signal was observed when lead(II) was injected into the mixture of potassium periodate and luminol in a flow-cell. The influencing factors on the PCL intensity of the system were investigated. Under the optimum experimental conditions, the present method allowed the determination of lead(II) in the concentration range of 1.0 × 10^?8 to 1.0 × 10^?5 mol/L and the detection limit for lead(II) was 2.3 × 10^?10 mol/L. The relative standard deviation was 3.2% for 11 replicate analyses of 1.0 × 10^?6 mol/L lead(II). Combined with cotton cellulose xanthate for separation, the proposed method was applied to the determination of lead(II) in real water samples with satisfactory results.     

SURFACTANT MEDIATED EXTRACTION OF TRITERPENES AND THEIR DIRECT HPLC ANALYSIS FROM THE MICELLAR SYSTEM

The pentacyclic triterpenes oleanolic acid (OA) and ursolic acid (UA) in Salvia triloba are attractive ingredients for cosmetic and pharmaceutical formulations. These triterpenoids are constitution isomers and differ only in the position of one methyl group in their chemical structures. Therefore it is difficult to achieve a baseline separation by standard RP-HPLC systems. Another challenge is that the complex plant contains a large variety of similar compounds. To achieve precise results for the target molecules, these compounds should be removed prior to analysis. Due to the large application of these two triterpenes, a fast quantification method is favored. If the triterpenes are extracted with aqueous two-phase systems, the target substances are enriched in a surfactant-rich phase. For this application, it is desirable to develop a method that is capable of quantifying both triterpenes directly by RP-HPLC without additional purification steps.

The optimal chromatographic conditions for pure substances as well as for crude surfactant-containing extracts were accomplished on a Nucleodur C18 ISIS column by isocratic elution with methanol/water/acetic acid/triethanolamine (90:10:0.04:0.02 v/v) as the mobile phase and a column temperature of 10°C. The flow rate was 0.6 mL/min, and the detection wavelength was 210 nm. With these parameters, a baseline separation was achieved and the calibration curve showed a very good linearity (R² > 0.999 for OA and UA) within the test range. The method is simple, rapid, and reliable for the quantification of crude extracts from plant material.     

Controlled Synthesis and Optical Properties of Pure Gold Nanoparticles

Abstract

Gold nanoparticles were synthesized by laser ablation of a gold metallic disc at wavelengths of 532 nm and 355 nm with 7 ns pulse duration in the pure water. The colloidal gold nanoparticles were characterized by ultraviolet-visible absorption spectroscopy, transmission electron microscopy, and fluorescence spectrometry. The presence of a surface plasmon resonance peak around ～ 524 nm indicates the formation of gold nanoparticles. The formation efficiencies of gold nanoparticles in colloids were found to increase when ablating the gold metallic disc with a laser having a longer wavelength. The size distributions of the gold nanoparticles thus produced were measured by transmission electron microscopy. A reduction in mean diameter of the particles was observed with a decrease in the laser wavelength under the irradiation at a high fluence of 25 mJ/pulse. The fluorescence spectroscopy demonstrated that these gold nanoparticles are fluorescent, showing a strong blue emission intensity at 458 nm.     

Spectrophotometric Determination of Silicon in Rice and Alloy Steel Samples

Abstract

In the medium of 0.128 mol/L nitric acid and 0.450 mol/L sulfuric acid, silicon(IV) and ammonium molybdate form molybdosilicate blue blue complex in the presence of ascorbic acid. The maximum absorption wavelength of the complex locates at 810 nm. The apparent molar absorptivity is ε_810 nm = 3.18 × 10⁴ L · mol^?1 · cm^?1. Beer's law is followed over the range of 0 ～ 1.0 µg/mLof silicon(IV). The present method has been successfully applied to the determination of silicon in rice and alloy steel samples.     

二氧化硅包覆对纳米多孔金增强荧光特性的调制

为了减弱金属基底对表面增强荧光的淬灭效应,设计了增强效果更好的荧光增强基底。采用化学生长二氧化硅的方法对纳米多孔金(NPG)表面进行修饰,避免荧光分子和NPG表面直接接触引起的淬灭效应,在SiO_2@NPG表面分别组装上罗丹明6G(R6G)和辐射中心波长为700 nm的量子点(QD 700)。通过探测分析荧光光谱,可以得出:二氧化硅包覆的基底可以使表面增强荧光得到显著的增强,并且二氧化硅厚度对荧光强度有调节作用;在基底增强量子点荧光信号的同时,量子点和NPG之间还出现非辐射的能量转移现象,二氧化硅的厚度对能量转移同样有调节作用,厚度约为5 nm时能量转移现象最显著。本实验为基于荧光能量转移的检测以及设计更好的荧光增强基底提供了参考。     

Investigation of Annealing Temperature on Structural and Morphological Properties of Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanoparticles for Humidity Sensor Application

Cr₂O₃ nanoparticles have been prepared for precipitation technique at reaction temperature 50 °C. The prepared samples were annealed different temperatures at 500,700 and 1000 °C. Synthesized powders were characterized as X-ray diffraction, optical, transmission electron microscope, SEM with EDAX, humidity sensor, FTIR. The annealing temperature has been found to be playing a crucial role in the controlling particle size. XRD study shows the rhombohedral crystal structure of highly preferential orientation along (1 0 4) direction. FTIR reveals that the presence Cr–O bonds in the structure. The TEM images show that the size of NPs of Cr₂O₃ varied from 26 to 60 nm with average crystalline size 43 nm. UV–visible spectrum shows the absorption band of Cr₂O₃ nanoparticles at 400 nm. The humidity sensor of the Cr₂O₃ nanoparticles was studied by two temperature method. 1000 °C annealed Cr₂O₃ nanoparticles show better sensing properties and exhibits good linearity in response than 500 °C. SEM images show the clusters and agglomeration of nanoparticles. EDAX spectrum confirms the presence of Cr₂O₃ nanoparticles. Each samples have been characterized as sensing materials to determine relative humidity in the range of 20–90%. The humidity sensing property increased with increasing of annealing temperature and the resistance was decreased.     

A MINIATURE SURFACE PLASMON RESONANCE BIOANALYTICAL SYSTEM FOR FIELD DETECTION OF MICROCYSTIN-LR IN SURFACE WATER

A miniature surface plasmon resonance (SPR)–based immunoassay system for analyzing microcystin-LR (MC-LR) in surface water has been developed. A Spreeta biosensor was adopted in the SPR flow injection analysis (FIA) system. An optional biofilm immobilization method was exploited using covalent-coupling between a bioconjugate of microcystin-LR and bovine serum albumin [(MC-LR)-BSA] and the golden surface. An acceptable relative standard deviation of repeatability, 1.29% (n = 20), was achieved. An analysis of the calibration curve showed that this method has a detection limit of 0.55 ng/mL, a half-maximal inhibitory concentration (IC₅₀) of 5.6 ng/mL, and a quantitative range of 1.56–25.00 ng/mL. The recovery from water samples containing varying concentrations of MC-LR ranged from 90% to 112%. After samples of tap water and pool water were assayed, it was concluded that tap water did not contain a measurable amount of the analyte, whereas pool water contained 2.39 ng/mL. Compared to other methods of analysis, SPR immunoassay has the advantage of being label-free, rapid, and cost-effective and can easily detect levels of MC-LR within the World Health Organization (WHO) drinking water guidelines. The SPR FIA system with reusable biosensor is compact and convenient for instant in situ determination of MC-LR levels in environmental water.     

PVC MATRIX MEMBRANE SENSORS FOR POTENTIOMETRIC DETERMINATION OF ARECOLINE

The construction and electrochemical response characteristics of Poly (vinyl chloride) (PVC) membrane sensors for arecoline HBr (AR) are described. The sensing membranes incorporate ion association complexes of (AR) cation and sodium tetraphenyl borate (NaTPB) (sensor 1) or phosphomolybdic acid (PMA) (sensor 2) or phosphotungstic acid (PTA) (sensor 3) as electroactive materials. The sensors display a fast, stable and near-Nernstian response over a relative wide AR concentration range (1 × 10^?2 – 4 × 10^?5 M) and (1 × 10^?2 to 5 × 10^?6 M), with cationic slopes of 52.5, 50.5 and 51.5 mV per concentration decade for sensor 1, 2, and 3, respectively over a pH range of 3.0–6.0. The sensors show good discrimination of AR from several inorganic and organic compounds. The direct determination of 1.5–2360.0 μg/ml of AR show an average recovery of 99.0, 98.5 and 99.5% and a mean relative standard deviation of 1.7, 1.6 and 1.5% at 200.0 μg/ml for sensor 1, 2 and 3 respectively. The proposed sensors have been applied for direct determination of AR in human saliva. The results obtained for determination of AR in saliva using the proposed method comparable favorably with those obtained using HPLC method.     

Tribochemical Transformation of Nano TiO2 to Ilmenite on the Surface of Wearing Steel Parts: Antiwear Action of Nano TiO2 as an Additive in Engine Oil

TiO₂ nanoparticles of average size about 20–30 nm were hydrothermally synthesized from TiCl₄ under mild acidic conditions. The nanoparticles were mixed with dispersant and base oil to give a partially transparent concentrate with 1.5 wt% of Ti content. The concentrate was dispersed in hexane and base oil to characterize, respectively, by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The concentrate was diluted with base oil to a parts per million level of Ti containing dispersion blends that were evaluated for wear and friction control performance. Nano TiO₂ containing fully formulated oil blend showed excellent load-bearing capability in Swingung, Reibung, Verschleiβ (SRV; oscillation, friction, wear) tests. Four-ball test results show that the wear scar diameter was considerably reduced to 0.30 mm for TiO₂-added blend compared to neat base oil (0.60 mm). The performance of TiO₂-added blend was comparable to secondary zinc dialkyl dithiophospate (ZDDP)-added blend under identical condition. Raman spectra of the worn surface on the tested ball revealed the presence of ilmenite (FeTiO₃) and no deposits of pure TiO₂.