Determination of water in ethanol and acetone by direct injection enthalpimetry based on the heat of dilution

Two analytical procedures based on the magnitude of the heat of dilution and direct injection enthalpimetry have been developed for determination of water in ethanol and acetone. The results obtained by means of the heat of dilution were compared with the values given by pycnometry, and gave a relative difference in the range 0.2-3%. The precision depends on the slope of the calibration curve, which varies with the procedure and the concentration of the sample.     

Determination of dye precursors in hair coloring products by liquid chromatography with electrochemical detection

The simultaneous determination of seven aminophenols, resorcinol and p-phenylenediamine in hair coloring products was performed by liquid chromatography (HPLC) with amperometric detection (ED). The aminophenols were separated on a ODS C18 reversed-phase column by isocratic elution with a mobile phase based on 0.1 M acetate buffer pH 4.5-methanol (90:10%, v/v) at a flow rate 0.8 mL min⁻¹. The limit of detection (S/N = 3) for the aminophenols was in the 15-40 pg (injected mass) range at an applied potential of 0.950 V versus Ag/AgCl. Peak heights for the aminophenols and the two others compounds were found to be linearly related to the amount injected, from 0.3 to 300 ng (r > 0.994-0.999).The relative standard deviation (R.S.D., n = 10) for 1 ng injected was comprised in the range from 2.5 to 6.2%, depending on the aminophenol tested. The present method minimizes troublesome and time-consuming pretreatment procedures and it was applied to the determination of aminophenols, resorcinol and phenylenediamine in hair coloring formulations.     

石墨烯基电化学传感器检测盐酸洛美沙星

利用滴涂法在玻碳电极表面修饰Nafion–石墨烯复合膜,制备电化学传感器,并利用差分脉冲溶出伏安技术间接测定盐酸洛美沙星的含量.对酸化的样品离子缔合物进行沉淀、离心分离,在支持电解质0.7 mol/L HSCN–KSCN中于–3.50 V下搅拌富集3 min,然后进行阳极极化扫描,可获得灵敏的阳极溶出峰,利用此法测定盐...     

High-performance liquid chromatography of gentian violet, its demethylated metabolites, leucogentian violet and methylene blue with electrochemical detection

High-performance liquid chromatographic conditions are reported for the electrochemical detection (ED) of Gentian Violet, its demethylated metabolites, Leucogentian Violet and Methylene Blue. Gentian Violet, its demethylated metabolites and Leucogentian Violet were separated within 14 min on a cyano column eluted isocratically with methanol-buffer (60:40) as the mobile phase. ED responses for Gentian Violet, Leucogentian Violet and Methylene Blue were linear over the ranges 0.54-6.75, 0.50-25.2, and 5.7-285 ng, respectively. Under these conditions, the compounds were eluted in the following order: Leucogentian Violet, N"-2-tetra-methylparaosaniline chloride, N'-1-tetramethylpararosaniline chloride, pentamethylpararosaniline chloride and Gentian Violet. Methylene Blue and Gentian Violet had essentially the same retention time under these parameters. The detection limit for Gentian Violet, its demethylated metabolites and Leucogentian Violet was determined to be 0.1 pmol. A detection limit of 3 pmol was established for Methylene Blue. Detector response, elution, separation, linearity and sensitivity of detection are discussed.     

Adsorption of ethyl violet dye in aqueous solution by regenerated spent bleaching earth

The adsorption of basic dye (i.e., ethyl violet or basic violet 4) from aqueous solution onto the regenerated spent bleaching earth (RSBE) was carried out by varying the process parameters such as initial concentration, pH, and temperature. As analytical comparisons, activated bleaching earth (ABE) was also used as adsorbent for the adsorption of the basic dye at various initial concentrations. The experimental results showed that the adsorption process can be well described with the pseudo-second-order reaction model and less fitted by the intra-particle diffusion model. The kinetic parameters of both models obtained in the present work are in line with pore properties of the two adsorbents. According to the equilibrium adsorption capacity from the fitting of pseudo-second-order reaction model, it was further found that the both models of Langmuir and Freundlich appeared to fit well the isotherm data. In addition, the thermodynamic parameters were evaluated based on the pseudo-second-order rate constants, showing that the adsorption of ethyl violet onto the RSBE is endothermic in nature.     

Determination of quercetin and its glucosides in onion by electrochemical methods

Quercetin (Q), quercetin-3,4'-diO-beta-glucoside (Q3,4'G), quercetin-3-O-beta-glucoside (Q3G) and quercetin-4'-O-beta-glucoside (Q4'G) were determined in onion bulbs (Allium cepa) by HPLC with amperometric detection after analysis of the hydrodynamic voltammograms of flavonoid standards within the potential range of 50-1000 mV and by cyclic voltammetry (CV) method. The hydrodynamic voltammetric profiles of flavonoids showed that the peak current of Q, Q3G, Q4'G and Q3,4'G increased rapidly when the applied potential exceeded +450 mV (vs. SCE). High sensitivity and low background current were observed at the applied potential of +950 mV (vs. SCE). The lower limits of detection (LOD) were determined at signal-to-noise ratio of 3 and showed the following values: 8.05x10(-8)M (Q), 1.08x10(-7) M (Q3G), 1.22x10(-7) M (Q4'G) and 2.6x10(-7) M (Q3,4'G). The data provided by HPLC-UV-MS confirmed the presence of Q, Q3G, Q4'G and Q3,4'G in 80% methanol extracts of lyophilised onion bulbs. The CV method was applied for the qualitative assessment of onion flavonoids followed by the determination of anodic peak potential (E(a)) of the standards. The qualitative analysis of onion flavonoids was based on the anodic peak current (I(a)) of the extracts after external standards addition. The recorded cyclic voltammograms of the above flavonoid standards showed that all four compounds had well-defined oxidation waves with peak potentials of 310, 390, 482 and 800 mV (vs. Ag/AgCl) for Q, Q3G, Q4'G and Q3,4'G in 50 mM acetate-acetic buffer (pH 5.5) in 80% methanol, respectively. The study proved applicability of the CV method for identifying Q, Q3G, Q4'G and Q3,4'G in onion.     

基于介孔碳的电化学酪氨酸酶生物传感器法测定水体中的苯酚及高效液相色谱法评价

采用新型的介孔碳材料作为固载酪氨酸酶的检测平台构建生物传感器,应用于水体环境中苯酚污染物的检测,并通过高效液相色谱法对电化学酪氨酸酶生物传感器法的准确性进行了评价。研究表明,介孔碳的"空间限制效应"能够防止酪氨酸酶(三维尺寸为6.5 nm×9.8 nm×5.5 nm)体外去折叠失活。基于介孔碳材料构建的电化学酪氨酸酶生物传感器在苯酚污染物检测方面显示了优良的性能,其重现性、灵敏度、稳定性、选择性以及检出限均比较令人满意。基于介孔碳的电化学酪氨酸酶生物传感器对苯酚污染物的检出限达到20 nmol/L,线性范围为0.1~10 μmol/L。采用基于介孔碳的电化学酪氨酸酶生物传感器和高效液相色谱法对实际水样品进行测定结果比对,结果表明该生物传感器方法检测结果准确、有效,适合于苯酚污染物突发污染事件的应急检测。     

克拉霉素的示波极谱测定及其电化学行为

在 0 .0 5mol LNaOH(pH 1 2 .7)介质中 ,克拉霉素在滴汞电极上产生一灵敏的还原峰 ,峰电位Ep=- 1 .35V(vs.SCE)。其一阶导数峰电流ip′与克拉霉素浓度在 8.0× 1 0 -6～ 4.8× 1 0 -5mol L范围内有良好的线性关系 (r=0 .9991 ) ,检出限为 4 .0× 1 0 -6mol L。此法已用于片剂的测定。用线性扫描和循环伏安法研究了体系性质 ,结果表明 ,克拉霉素的电极过程为具有吸附的不可逆过程     

"One-step" simplified electrochemical sensing of TATP based on its acid treatment

A fast, simple and sensitive electrochemical method for sensing peroxide-based explosives based on their acid treatment is reported. The method relies on the high electrocatalytic activity of Prussian-blue (PB)-modified electrodes towards the acid-generated hydrogen peroxide in the harsh acidic medium (down to pH 0.3) used for releasing hydrogen peroxide. Such effective operation of PB electrochemical sensors in strongly acidic media eliminates the need for an additional neutralization step required in analogous peroxidase-based assays (due to acid-induced enzyme deactivation processes). Factors affecting the efficiency of the acid pre-treatment of triacetone triperoxide (TATP) have been examined and optimized to allow its sensitive measurement down to the 50 ng level within 60 s. Chronoamperometric detection of microgram amounts of solid TATP, following a one-minute acid mixing and placing a 20 microL droplet onto a disposable PB-modified screen-printed electrode is illustrated. Similar results were obtained for the peroxide explosive hexamethylene triperoxide diamine (HMTD). By greatly simplifying the analytical procedure, such an acid-operated "artificial peroxidase" electrocatalytic transducer holds great promise for designing "one-step", user-friendly, miniaturized, cost-effective devices for field screening of peroxide explosives.     

Determination of urinary vanillylmandelic acid by direct injection and coupled-column chromatography with electrochemical detection

An automated column-switching system for determination of vanillylmandelic acid in urine is described. The liquid chromatographic system was composed of two separation columns with different selectivity properties, an octadecyl column coated with tributyl phosphate as stationary liquid phase and a silica-based anion exchanger. Urine samples were injected directly onto the first column, where vanillylmandelic acid was separated from the main part of the sample matrix. The internal standard isovanillylmandelic acid was co-eluting with vanillylmandelic acid, and a fraction of the eluate containing both substances was switched to the second column, where separation was performed. To assess peak purity, detection was performed with dual working electrodes in parallel mode. A relative standard deviation of 3.5% was obtained for determination of human urine samples containing 3 microM vanillylmandelic acid, and less than 0.1 microM could be detected.     

Detection of catechin based on its electrochemical autoxidation

Catechins are strong autoxidant to produce steady intermediate in alkali solution. In present work, we, for the first time, developed a electrochemical method based on ruthenium tris (2, 2′) bipyridyl (Ru(bpy)₃³⁺) modified boron-doped diamond (BDD) electrode to investigate the electrochemical reduction of catechin autoxidation intermediate with its existence verified by the electron spin resonance (ESR). The reduction peak potential was observed at −855.5 mV, not appearing either in acid solution (pH 2) containing catechins or in oxidized catechin solution (pH 12). Moreover, the effects of pH, ascorbic acid, Cu²⁺, Fe²⁺ and autoxidation time are investigated, demonstrating the reduction peak being really the reduction of catechin autoxidation intermediate. It is found that the peak current is proportional to scan rate, indicative of a surface confined reduction process. Sensitive amperometric response was obtained covering linear range from 0.3268 μM to 0.1591 mM. The determination of catechin in commercial preparations using this method shows satisfactory results comparable with those of the traditional methods.     

Determination of Violet Covasol as a cosmetic dye in water samples by a CPE-Scanometry method

The trace amounts of Violet Covasol as a cosmetic dye was determined by an efficient cloud point extraction-Scanometry(CPE-Scanometry) method. This method has many advantages such as novelty,facility, high speed, sensitivity, low cost and safety. The method is based on the CPE of an analyte from an aqueous solution, diluting the extracted surfactant-rich phase with ethanol, transferring to Plexiglas~cell and scanning of the cells containing the analyte solution with a scanner and measuring the RGB parameters with software written in visual basic(VB 6) media. Parameters impacting the extraction efficiency such as p H of the system, the concentration of surfactant, equilibration temperature and time were optimized. Detection limit(DL), relative standard deviation(RSD) and linear range for the proposed method are 0.026, 0.71 and 0.16–6.6 μg m L ~(-1)respectively. The method was successfully applied for the determination of Violet Covasol dye in several water samples, including a water sample containing the dye as a tracer(to investigate subsurface water movement).     

溴甲酚紫分光光度法测定水中的阴离子表面活性剂

在pH=2的酸性条件下,十二烷基苯磺酸钠(SDBS)阴离子表面活性剂能与溴甲酚紫直接缔合,生成浅黄色缔合物;据此建立了测定水中SDBS阴离子表面活性剂的分光光度法.结果表明,生成的浅黄色缔合物的最大吸收波长为436nm,SDBS的表观摩尔吸光系数为1.68×104 L·mol-1·cm-1;SDBS的浓度在0²mg·L-1范围内时遵循比尔定律.该方法可方便地用于测定水样中的痕量阴离子表面活性剂,效果良好.     

TNT determination based on its degradation by immobilized HRP with electrochemical sensor

Based on the mechanism of 2,4,6-Trinitrotoluene (TNT) degradation, an amperometric hydrogen peroxide biosensor was constructed for the determination of trace amounts of TNT by immobilization of MWCNTs, HRP and Nafion onto the surface of glassy carbon electrode (GCE). The Nafion/MWCNTs/HRP biosensor was capable of degrading TNT with the consumption of H₂O₂ and HRP in 0.2 mol/L PBS (pH 7.0). Trace TNT was quantitative analyzed by the current decrease of H₂O₂ at the reductive potential of −0.35 V using cyclic voltammetry (CV). Effect of the ratio of MWCNTs/HRP, initial concentration of H₂O₂ and electrolyte’s pH were also optimized by CV. Under the optimal conditions, the current decrease of H₂O₂ that was consumed by TNT degradation was proportional to TNT ranging from 8.8 × 10⁻⁹ mol/L to 2.64 × 10⁻⁷ mol/L with a detection limit of 3.0 × 10⁻⁹ mol/L (S/N = 3). It developed a new way for simple, rapid and sensitive measurement of trace TNT.     

A novel sensing platform based on self-doped TiO2 nanotubes for methylene blue dye electrochemical monitoring during its electro-Fenton degradation

Journal of Solid State Electrochemistry - The synthesis of a self-doped TiO2 nanotubes (SD-TNT) electrode and its potential applicability as a sensing platform electrode for voltammetric...     

Determination of trace metal ions by AAS in natural water samples after preconcentration of pyrocatechol violet complexes on an activated carbon column

A simple preconcentration method is described for the determination of Cu, Mn, Co, Cd, Pb, Ni and Cr in water samples by flame AAS. Trace metal ions in water were sorbed as pyrocatechol violet complexes on activated carbon column at the pH range of 4–8, then eluted with 1 M HNO₃ in acetone. The effect of major cations and anions of the natural water samples on the sorption of metal ions has been also investigated. The concentration of the metal ions detected after preconcentration was in agreement with the added amount. The present method was found to be applicable to the preconcentration of Cu, Mn, Co, Cd, Pb, Ni and Cr in natural water samples with good results such as R.S.D. from 3 to 8% (N=10) and detection limits under 70 ng l⁻¹.     

Removal of organic dye pollutants from wastewater by electrochemical oxidation

The removal of chemical oxygen demand (COD) and color from simulated dye wastewater containing organic dyes, direct yellow 4, C₂₆H₂₀N₄O₈S₂Na₂ and acid yellow 17, C₁₆H₁₀O₇N₄S₂Cl₂Na₂ experimentally investigated using an electrochemical undivided cell reactor with Pt as anode and steel as cathode. Particular attention was paid to probe the effect of supporting electrolyte (NH₄Cl), cell voltage, pH, and treatment time on the electrochemical treatment efficiency. Experiments were also carried out using 0.2?M NH₄Cl as supporting electrolyte under the condition of free pH. The experimental results showed that the process could efficiently remove the color and COD from simulated dye waste water. The overall COD removal reached at 69.9% by using supporting electrolyte and increasing voltage. The process can be described by pseudo first-order kinetics for the removal of COD.     

Determination of tungsten with pyrocatechol violet by first-derivative solid-phase spectrophotometry

Derivative spectrophotometry was applied to solid-phase spectrophotometry in order to enhance its sensitivity and remove the large background caused by the absorbance of the resin layer. Determination of micro-amounts of tungsten with pyrocatechol violet to form a 21 green complex in acid medium which is fixed on a dextran-type anion-exchange resin (Sephadex QAEA-25) is described as an example for the application of this technique. The absorbance of the resin packed in a 1-mm spectrophotometric cell, was measured directly. The characteristic peak amplitude of the signal at 674 nm in the first-derivative spectrum is useful for quantitative determination of tungsten (3–16 g 1^–1; RSD 5.8%) in natural and industrial water samples.     

Determination of aromatic amines in water samples by capillary electrophoresis with electrochemical and fluorescence detection

Two capillary electrophoresis methods have been compared for the determination of aniline derivatives in environmental water samples. With the first method the anilines were separated as cations by free zone electrophoresis at low pH, and detected by amperometry. For this, the separation capillary was connected through a palladium field decoupler to an electrochemical detection cell which had been modified to match the volume scale of the separation. Most anilines tested, except chlorinated compounds, could be detected with full sensitivity at a detection potential of +0.7 V. Detection limits with this detection scheme were on a low microg/l level. The alternative method involved the derivatization of the anilines with fluorescamine, the separation of the derivatives formed by micellar electrokinetic chromatography, and fluorescence detection. For detection a lamp-based, fibre optics instrument was used. Detection limits with fluorimetry were comparable with those obtained with amperometric detection (in the order of 1 microg/l). Still, this method was preferred since it gave a higher separation efficiency and shorter analysis times (approximately 4 min). The most important argument, however, was its higher reliability and ease-of-handling. Preliminary experiments with water samples collected in areas where pollution with anilines may be expected showed that the method is highly specific, with few interferences showing up in the electropherograms.