Standard addition method applied to solid-state stripping voltammetry: determination of zirconium in minerals and ceramic materials

An application of the standard addition method to stripping voltammetry of solid materials immobilized in inert electrodes is described. The method allows the determination of the mass fraction of a depositable metal M in a material on addition of known amounts of a standard material containing M to a mixture of that material and a reference compound of a second depositable metal, R. After a reductive deposition step, voltammograms recorded for those modified electrodes immersed in a suitable electrolyte produce stripping peaks for the oxidation of the deposits of M and R. If no intermetallic effects appear the quotients between the peak areas and the peak currents for the stripping oxidation of M and R vary linearly with the mass ratio of the added standard and the reference compound, thus providing an electrochemical method for determining the amount of M in the sample. The method has been applied to the determination of Zr in minerals, ceramic frits, and pigments, using ZnO as reference material and ZrO₂ as the standard.     

H-point standard addition method applied to solid-state stripping voltammetry: quantitation of lead and tin in archaeological glazes

A solid-state electrochemical application of the H-point standard addition method to the quantification of two depositable metals A and B, which produce strongly overlapped stripping peaks, is described. The method is based on the mechanical transference of mixtures of the solid sample plus a selected compound, of a reference depositable metal R, and of known amounts of a reference material containing A or B, to paraffin-impregnated graphite electrodes. After a reductive deposition step, voltammograms recorded for those modified electrodes immersed into a suitable electrolyte produce stripping peaks for the oxidation of all of the metals deposited. Measurement of the currents at selected potentials in overlapping peaks corresponding to the stripping of A and B permits the quantitation of these metals in the solid sample, while avoiding matrix effects. The method was applied to the simultaneous determination of Pb and Sn in archaeological glazes using PbCO₃ and SnO₂ as standards and ZnO as a reference material.      

Voltammetric Studies on Chromotrope 2B‐Protein Interaction and Its Analytical Application

In this paper the interaction of chromotrope 2B (Ch2B) with proteins was studied by the electrochemical method. Ch2B is an azo dye and shows irreversible electrochemical responses on the mercury electrode in a pH 3.0 Britton‐Robinson (B‐R) buffer solution. After the addition of human serum albumin (HSA) into the Ch2B solution, an interaction took place, and a supramolecular complex was formed in the mixed solution. The electrochemical parameters of the Ch2B‐HSA interaction system were calculated and compared. The results showed that in the absence and presence of HSA in Ch2B solution, the electrochemical parameters such as the formal potential E⁰, the electrode reaction standard rate constant k_s, etc. showed no significant changes, which indicated that an electro‐inactive supramolecular biocomplex was formed. The free concentration of Ch2B in reaction solution was decreased, and this resulted in the decrease of the peak current. The binding constant and the binding ratio were calculated as 7.85 × 10⁹ and 1:2, respectively, and the interaction mechanism was discussed. Based on the decrease of the peak current, this new electrochemical method was proposed for the determination of HSA in the concentration range of 2.0?25.0 mg/L with the linear regression equation as ΔIp′ (nA) = 50.56C (mg/L) — 6.72 (γ = 0.995). This method was further used to determine other different kinds of proteins, such as bovine serum albumin (BSA), oval albumin, etc‥ The new method was successfully applied to detect the content of albumin in healthy human serum samples with the results in good agreement with the traditional Coomassie Brilliant Blue G‐250 spectrophotometric method.     

Simultaneous Spectrophotometric Determination of Aluminum and Iron in Micellar Media by Using the H‐Point Standard Addition Method

A very simple spectrophotometric method for simultaneous determination of aluminum(III) and iron(III) based on formation of their complexes with pyrocatechol violet (PCV) in micellar media, using the H‐point standard addition method (HPSAM), is described. In micellar media, the metal complexes of Al‐PCV and Fe‐PCV are formed very fast. Formation of both of the complexes was complete within 5 min at pH 8.5. The linear ranges for aluminum and iron were 0.05‐2.50 and 0.10‐4.00 μg mL^?1, respectively. The relative standard deviation (R.S.D.) for the simultaneous determination 0.40 μg mL^?1 of Al(III) and 0.20 μg mL^?1 of Fe(III) were 3.24% and 4.22%, respectively. Interference effects of common anions and cations were studied. The method was applied to simultaneous determination of Al(III) and Fe(III) in standard reference material and alloy samples.     

Constant Current Chronopotentiometric Stripping Analysis of ‘N‐Catalyst’ in Sodium Chloride Solution and Seawater

Catalytic properties and surface activity of nitrogen containing polymeric organic material (N‐POM) were analyzed by constant current chronopotentiometric stripping analysis (CPSA) and alternating current (AC) voltammetry in sodium chloride solution (pH 8) and seawater. CPSA proved to be a suitable method for determination of low concentrations of N‐POM in seawater by measuring its ‘presodium’ catalytic peak H. A protein human serum albumin (HSA) (15% of N) was used as a model compound and the concentration of N‐POM from natural seawater samples was expressed in HSA concentration equivalents. Peak H represents an additional parameter for characterization of natural organic matter.     

A New Electrochemical Method for the Determination of Proteins with Cupferron‐Cadmium(II) Complex

A new electrochemical method was proposed for the determination of trace amounts of proteins based on the cupferron (Cup) and cadmium(II) complex [Cup‐Cd(II)] as the voltammetric probe. In the selected pH 6.5 Britton–Robinson (B–R) buffer solution, Cup can interact with Cd(II) to form a stable complex of [Cup‐Cd(II)], which had a sensitive linear sweep voltammetric reductive peak at ?0.654 V (vs. SCE). The addition of human serum albumin (HSA) into [Cup‐Cd(II)] complex solution could greatly decrease the reductive peak current without the change of the reductive peak potential, which indicated that HSA could interact with [Cup‐Cd(II)] complex to form a supramolecular biocomplex. The interaction mechanism was discussed and the decrease of reductive peak current was proportional to the concentration of HSA, which could be further used for the proteins determination. The optimal conditions of the binding reaction and the electrochemical detection were carefully investigated. Under the optimal conditions a new quantitative determination method for different kinds of proteins such as HSA, bovine serum albumin (BSA) and bovine hemoglobin (BHb) etc. was developed. The proposed method was simple, practical and relatively free from the interferences of coexisting substances, and it was further applied to the samples determination with satisfactory results. The binding constant (β_s) and the binding number (m) of HSA with [Cup‐Cd(II)] complex were calculated by the voltammetric data with the results as β_s=1.12×10⁶ and m=1.     

Electrochemical Studies of the Neuraminidase Inhibitor Zanamivir and its Voltammetric Determination in Spiked Urine

Zanamivir is a member of a new class of antiviral agents that selectively inhibit the enzyme neuraminidase of influenza A H5N1 and H1N1 viruses. Although zanamivir is the compound of biological interest, so far it has not been a subject of any electrochemical studies. It was stated, that zanamivir can act as an electrocatalyst at HMDE. The electrode mechanism is connected with the hydrogen evolution reaction catalyzed by zanamivir as the guanidine compound. A new adsorptive catalytic method for its voltammetric (SW AdSV) determination was developed. The dependence of the peak current on pH, buffer concentration, nature of the buffer and instrumental parameters were studied. The best results were received in citrate‐phosphate buffer at pH 2.2. This electroanalytical procedure enabled to determine zanamivir in the concentration range 4.8×10^?7–1.2×10^?5 mol L^?1 in supporting electrolyte and diluted urine. Precision, repeatability and accuracy of the method were checked in both media. The detection and quantification limits were found to be 1.5×10^?7 and 4.8×10^?7 mol L^?1 respectively. A standard addition method was used to determine zanamivir in spiked urine.     

Electrochemical Studies on the Interaction of Heparin with Phenosafranine and Its Analytical Application

The interaction of phenosafranine (PSF) with a glycosaminoglycan of heparin (Hep) in aqueous solution was characterized by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) in this paper and further used for Hep detection. In pH 1.5 Britton‐Robinson (B‐R) buffer solution PSF had a well‐defined voltammetric reductive peak at ?0.256 V (vs SCE), and the electrochemical response was faded by the addition of Hep. Cyclic voltammetric experiments indicated that the electrochemical behaviors of free PSF didn't change no matter whether Hep was presented in PSF solution or not. Based on the decrease of the peak current, a second order derivative linear sweep voltammetry was used to establish a sensitive electroanalytical method for Hep. The peak current was proportional to the concentration of Hep in the range of 0.7～20.0 mg L^?1, demonstrating that this method was suitable for routine Hep detection. Under optimal conditions, the linear regression equation for the Hep determination was ΔIp”(nA) = 46.30 C (mg L^?1) + 343.31 (n = 11, γ = 0.991) with a detection limit of 0.08 mg L^?1 (3σ). The established method was further successfully applied to heparin sodium injection samples determination. The interaction mechanism was discussed based on the electrostatic attraction of the negatively charged Hep with the positively charged PSF, and the stoichiometry of Hep‐PSF was calculated by the voltammetric method.     

Voltammetric Detection of the DNA Interaction with Toluidine Blue

Binding reactions of toluidine blue (TB) with herring fish DNA in pH 6.0 Britton–Robinson (B–R) buffer solution have been investigated by cyclic voltammetry and linear‐sweep voltammetry at a glassy carbon electrode. TB has a couple of well‐defined redox peaks. The addition of DNA into the TB solution resulted in the decrease of the redox‐peak currents and the shift negatively of the anodic peak potential. The values of the electrochemical parameters such as the electron number of the electrochemical reaction, the electron transfer coefficient and the electrochemical reaction standard rate constant in the absence and presence of DNA, as well as the values of binding constant and binding ratio of DNA with TB were obtained. Almost unchanged values of the electrochemical parameters in the absence and presence of DNA show that nonelectroactive complexes were formed when TB interacted with DNA. DNA concentration can be determined by the decrease of the peak current of TB. The binding mode of TB with DNA was discussed.     

Novel Thiazolo[5,4‐d]thiazole‐Based Organic Dyes for Quasi‐Solid‐State Dye‐Sensitized Solar Cells

A series of novel metal‐free organic dyes containing the thiazolo[5,4‐d]thiazole moiety were designed and synthesized for quasi‐solid‐state dye‐sensitized solar cells (DSSCs). Different alkoxy chains were introduced into the electron donor part of the dye molecules for comparison. The optical, electrochemical, and photovoltaic properties for all sensitizers were systematically investigated. It was found that the sensitizers with the different alkoxy groups have similar photophysical and electrochemical properties, such as absorbance and energy levels, owing to their close chemical structures. However, the quasi‐solid‐state DSSCs based on the resulting sensitizers exhibit different performance parameters. The quasi‐solid‐state DSSC based on sensitizer FNE74 with two octyloxy chains possessed the highest solar energy conversion efficiency of 5.10 % under standard AM 1.5G sunlight illumination without the use of coadsorbant agents.     

Simple and Feasible Simultaneous Determination of Three Phenolic Pollutants on Boron‐Doped Diamond Film Electrode

A simple, rapid and feasible method is developed for direct and simultaneous determination of phenol (Ph), hydroquinone (HQ) and 4‐nitrophenol (4‐NP) on unmodified boron‐doped diamond (BDD) electrode. Results showed that the oxidative peaks of these three phenolic compounds can be completely separated on BDD electrode in acidic conditions by using electrochemical cyclic voltammetry technique. The peak potential separations are all higher than 0.35 V. Moreover, BDD electrode is extremely easy to be refreshed to obtain current values with good reproducibility, even if it is passivated by phenolic compounds with different adsorption characteristics. All the above features are on account of the outstanding electrochemical characteristics of BDD electrode, and lead to the advantage and feasibility for simultaneous determination of three phenolic compounds without any other separation operation. For each tested phenolic compound, the concentration range with linearity is in two or three orders of magnitude in the presence of other coexisting phenolic compounds with the concentrations more than 1000 times higher than that of the tested component. The present method is also shown to be promising for the determination of phenolic contaminants in the real wastewater samples.     

普鲁士蓝/氧化锆复合材料的电化学行为及对H2O2的电催化

通过一步电沉积技术制备了普鲁士蓝/氧化锆修饰玻碳电极。采用电化学阻抗技术表征修饰电极。采用循环伏安法研究了pH值和扫描速率对该修饰电极的电化学行为的影响。结果表明:普鲁士蓝的峰电流与其扫描速率的一次方在一定范围内呈良好的线性关系。此外,该修饰电极在含有KCl(1.0mol/L)的磷酸盐缓冲溶液(0.1mol/L,pH=7.0)中,对H2O2具有明显的电催化作用,在无酶检测H2O2领域具有潜在的应用价值。     

Novel Approach for Rapid and Efficient Synthesis of 2‐(3‐(4‐Aryl)‐1‐isonicotinoyl‐4,5‐dihydro‐1H‐pyrazol‐4‐yl)‐3‐phenylthiazolidin‐4‐one Derivatives and Screened Their Antimicrobial Activity

A series of compounds, viz. 2‐(3‐(4‐aryl)‐1‐isonicotinoyl‐4,5‐dihydro‐1H‐pyrazol‐4‐yl)‐3‐phenylthiazolidin‐4‐one 4 ( a – n ), have been synthesized by reaction of 3 ( a – n ) with thioglycolic acid in the presence of zinc chloride. Compounds 3 ( a – n ) have been synthesized by amination of formylated pyrazoles 2 ( A – B ), which were synthesized by formylation of 1 ( A – B ) by Vilsmeier–Haack reagent (POCl₃/DMF). Compounds 1 ( A – B ) were synthesized by condensation of hydrazide and substituted acetophenones under conventional method and microwave irradiation method. These compounds were identified on the basis of melting point range, Rf values, infrared, ¹H NMR, and mass spectral analysis. These compounds were evaluated for their in vitro antimicrobial activity, and their minimum inhibitory concentration was determined. Among them, compound 4b and compound 4l possess appreciable antimicrobial and antifungal activities. Antibacterial activity results showed that compounds containing electron‐withdrawing groups were more active than compounds containing electron‐releasing groups.     

Quantitative analysis of an oligomeric hindered amine light stabilizer in polypropylene by matrix-assisted laser desorption/ionization mass spectrometry using a solid sampling technique

A small amount of an oligomeric hindered amine light stabilizer (HALS) (Adekastab LA-68LD) in polypropylene (PP) materials was directly determined by solid sampling matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) using an internal standard method. First the matrix reagent (dithranol), 20 mg, and the empirically selected internal standard, angiotensin I (MW = 1296.5), 5 microg, were premixed in the solid state. The matrix mixture was then co-ground with the PP sample containing the HALS in liquid nitrogen using a freezer mill. The powdered sample mixture was spotted on the sample plate, suspended in ion-exchanged water, dried to adhere on the plate, and subjected to MALDI-MS. Three series of the HALS components accompanied by the oxidized species were clearly observed as their molecular ions (M*+)) along with that of the internal standard in the mass spectra. A fairly good linear relationship (R2 = 0.9991) with a relative standard deviation of ca. 11% was observed between the relative peak intensities of the HALS components and the HALS contents ranging from 0.1-2.5 wt%, which could be used as the calibration line to determine the HALS content in PP composites directly by MALDI-MS. The UV-exposed PP composite samples were evaluated by this method to interpret the photostabilizing action of HALS in the PP materials based on the observed change in the relative abundances of the original and oxidized HALS components as a function of UV-exposure time.     

Electron‐Deficient Tetrabenzo‐Fused Pyracylene and Conversions into Curved and Planar π‐Systems Having Distinct Emission Behaviors

Polycyclic aromatic compounds containing fully unsaturated five‐membered ring(s) have been intensively studied because of their unique properties, which include high electron affinity and reactivity. Reported herein is an efficient route for the synthesis of tetrabenzo‐fused pyracylene, which comprises pyracylene and tetracene segments, using intramolecular oxidative C? H coupling. It was shown to possess high electron affinity and was found to undergo addition reactions with n‐butyllithium or benzyne. These reactions led to either a 1,4‐addition compound or triptycene‐type adduct with a curved or planar π‐system, respectively. Although these compounds exhibited similar sky‐blue emissions in a dilute solution, the emission band of the 1,4‐addition compound was significantly red‐shifted in the solid state and exhibited intense yellow emission attributable to the excimer, while the triptycene‐type adduct retained the intense blue color emission in the solid state.     

Simultaneous Determination of Copper and Bismuth by Anodic Stripping Voltammetry Using H‐Point Standard Addition Method with Simultaneous Addition of Analytes

Simultaneous determination of bismuth and copper by anodic stripping voltammetry using H‐point standard addition method (HPSAM) with simultaneous addition of analytes is described. The effect of various parameters including acid concentration, accumulation time, accumulation potential and concentration ratio of analytes in the standard solution on the sensitivity and accuracy of method were investigated. The results of applying the H‐point standard addition method showed that Cu²⁺ and Bi³⁺ could be determined simultaneously with the concentration ratios of Cu²⁺ to Bi³⁺ varying from 1 : 15 to 16 : 1 in the mixed sample. The method was successfully applied to the simultaneous determination of copper and bismuth in some synthetic mixtures.     

Voltammetric Determination of Boric Acid Using the Ternary Complexation System with Salicylaldehyde and H‐Acid

A square‐wave voltammetric method for the determination of boric acid in water has been described based on the new understanding of the electrochemical behavior of boric acid‐Azomethine H complexation. Salicylaldehyde and H‐acid were used as the starting materials of boric acid‐Azomethine H complex and their concentrations were optimized for boric acid determination in water. A glassy carbon electrode, instead of a conventional mercury electrode, was used in the measurement. The detection limit of the proposed method was 0.10 mg B dm^?3. The proposed method was successfully used for boric acid determination in the water from a seawater desalination RO plant.     

Simultaneous Determination of Ultra Trace of Uranium and Cadmium by Adsorptive Cathodic Stripping Voltammetry Using H‐Point Standard Addition Method

A sensitive adsorptive cathodic stripping voltammetry with H‐point standard addition method for simultaneous determination of uranium and cadmium has been developed. The trace amounts of these metal ions can be simultaneously determined using the Levodpa as complexing agent. Optimal conditions were: accumulation time 50 s, accumulation potential 0.0 mV, scan rate 40 mV s^?1, supporting electrolyte 0.1 M ammonium buffer pH 9.6, and 1×10^?5 M of Levodopa. The results revealed that the cadmium and uranium could be simultaneously determined by H‐point standard addition method with different concentration ratios of uranium to cadmium. The method was successfully applied in a several of real samples.     

Three-phase interlines electrochemically driven into insulator compounds: a penetration model and its verification by electroreduction of solid AgCl

A dynamic three-phase interline model has been developed for the reduction of a solid insulating metal compound to the metal in a suitable electrolyte, focusing on the electrochemically driven penetration of the process (or the three-phase interlines) into the insulator. Consideration is given to the effects of electrochemical, concentration and ohmic polarizations in the reduction-generated porous metal layer on top of the solid compound. Under potentiostatic conditions, reduction in the depth direction (penetration) becomes progressively slower as a result of the rising ohmic and concentration polarizations, whilst the electrochemical polarization exerts a declining effect. The quantitative equations established here also provide simple methods for the determination of some kinetic parameters of the reduction process, including rho (total resistivity) and D(R) (diffusion coefficient). The model has been experimentally verified by electrochemical reduction of solid AgCl with two novel metal|AgCl cylinder electrodes in aqueous solutions.     

Calibration of solid sampling Zeeman atomic absorption spectrophotometry by extrapolation to zero matrix

Summary A new method is described for the calibration of solid sampling Zeeman atomic absorption spectrophotometry, which can be applied independently of the use of certified reference materials. The specific signal (peak height divided by analyte mass or peak height divided by sample mass, for standard and sample, resp.) is plotted as a function of the analyte or the sample mass, and the line is extrapolated to zero mass. It is believed that this gives a specific signal not influenced by deviations from linearity of the calibration curve and free from matrix effects. The method yielded good results for Zn, Cd and Pb in several certified reference materials.Presented at the 5th International Colloquium on Solid Sampling with Atomic Spectroscopy, May 18–20, 1992; Geel, Belgium. Papers edited by R. F. M. Herber, Amsterdam