Scanning Potential Range Research Articles

Dual-potential ratiometric electrochemiluminescence based on single emitter and single coreactant for the sensitive detection of carcinoembryonic antigen

Dual-potential ratiometric electrochemiluminescence (ECL) is in favor of resistance to environmental interference. However, two kinds of emitters or coreactants, and a wide scan potential range (>2 V) are mandatory. This work developed a new dual-potential ratiometric ECL sensor for detection of carcinoembryonic antigen (CEA) using single emitter (luminol) and single coreactant (H2O2) with a mild potential range from −0.1 to 0.6 V. Luminol could produce a strong cathodic ECL (Ec) induced by hydroxyl radicals (HO‧) from the reduction of H2O2, and a relatively weak anodic ECL (Ea). After the ferrocene modified CEA aptamer (Apt-Fc) was attached, Fc could promote Ea by catalyzing the oxidation of H2O2, and reduce Ec by consuming HO‧. With the cycling amplification of the exonuclease I, CEA could substantially reduce the amount of Apt-Fc, resulting in the decrease of Ea and the rise of Ec. So, the ratio of Ec to Ea (Ec/Ea) was used as the detection signal, realizing the sensitive determination of CEA from 0.1 pg mL−1 to 10 ng mL−1 with a LOD of 41.85 fg mL−1 (S/N = 3). The developed sensor demonstrated excellent specificity, stability and reproducibility, with satisfactory results in practical detection.

Electrochemical Polymerization of a Novel Thiophene-Derived Monomer and Its Use as Support Material for Methanol Oxidation

This research, conductive polymer supported modified electrode system which was prepared for usage in direct methanol fuel cells. To test the behavior of these electrode system for methanol oxidation, cyclic voltammetry (CV), chronoamperometry (CHR) and electrochemical impedance spectroscopy (EIS) methods were used as electrochemical methods. As the working electrode, pencil graphite electrode (PGE) was preferred because of its porous structure, good ion conductivity, practicality in application and ease of preparation and obtaining. Thiophene derivative 4,4')-2,2'-(diazen-1,2 diylbis(4,1 phenylene))bis(4 (thiophene-2-ylmethylene) oxazol-5(4H)-one), (DiAzBiPhBiTyOx) monomer was prepared and electrochemically polymerized by CV method in 0.01M TBAP and 0.05 HClO4 containing ACN solution on the surfaces of PGE. The spectroscopic characterization of the synthesized monomer was performed by NMR spectroscopy. Optimum polymerization conditions of monomer was determined according to scanning rate, potential range and acid density. The obtained modified electrode system (PGE/PDiAzBiPhBiTyOx) was doped with chloroplatinic acid hexahydrat-Pt2Cl6.6H2O (Pt) at different densities and the optimum catalyst density was determined as 3.25mM (PGE/3.25mMPt@PDiAzBiPhBiTyOx). The methanol oxidation performances of conductive polymer film, platinum and conductive polymer supported platinum catalyst systems were investigated separately. While the methanol oxidation responses of the conductive polymer film and platinum are almost similar, the methanol oxidation response of the platinum doped conductive polymer film catalyst system is higher. The modified electrode characterization was performed by CV, CHR and EIS methods. Furtheremore obtained modified electrode systems were characterized by FESEM/EDS, XRD to confirm the structures and morphologies. Also, the theoretical values such as electrochemical surface area (ECSA) and specific capacitance (Cs) were calculated in aqueous acidic solution with and without methanol. Cs values of the PGE/3.25mMPt@PDiAzBiPhBiTyOx electrode in aqueous acidic solution with and without methanol were 3.861 and 3x10-4Fg-1 respectively. Also, the electrochemical surface area values of the same electrode in aqueous acidic solution with and without methanol were 196.437 and 21.150m2g-1 respectively.

Preparation and characterization of polydodecyl benzene sulfonic acid/ polyaniline

Poly dodecyl benzene sulfonic acid/polyaniline (PDBSA/PANI) composite was prepared by twice electropolymeization. The effects of experiment conditions such as DBSA concentration, elecrode length, twice scan potential range, scan rate and scan cycles on the charge capacity of PDBSA/PANI composite were investigated. And the optimum twice electropolymerization parameters were achieved. The functuional group and surface micrograph of PDBSA/PANI composite were characterized by FT-IR spectra and field emission scanning electron microscope, respectively. The results showed that the absorption intensities of sulfonic acid group originated from PDBSA/PANI were much more stronger than those of self-adsorbed DBSA/PANI composite. Meanwhile, the surface micrograph of PDBSA/PANI was much more fibrous than that of DBSA/PANI. All the above were advantage to the storage of charge. Thus, PDBSA/PANI was better than DBSA/PANI in charge storage.

Tuning Dimensionality of Benzimidazole Aggregates by Using Tetraoctylammonium Bromide: Enhanced Electrochemiluminescence Studies

Exploring the depolymerization strategy of liposoluble luminophores in the aqueous phase is vital for the development of electrochemiluminescence (ECL). In this work, tetraoctylammonium bromide (TOAB) with four long hydrophobic chains and short hydrophilic ends is used as a template to limit the aggregation of benzimidazole (BIM). By adjusting the loading of BIM on the hydrophobic chains of TOAB, a two-dimensional lamellar BIM/TOAB is formed, the ECL intensity of which is 6.4 times higher than that of the aggregated BIM (H2O2 as the coreactant). In terms of ECL spectroscopies, cyclic voltammetry , ECL transients, and the adjustment of the scanning potential range, the ECL mechanism is thoroughly studied. This work provides a new way to depolymerize organic luminophores and reveals a possible pathway in the annihilation ECL mechanism.

A dual-emitting immunosensor based on manganese dioxide nanoflowers and zinc sulfide quantum dots with enhanced electrochemiluminescence performance for the ultrasensitive detection of procalcitonin.

A dual-emitting electrochemiluminescence (ECL) immunosensor based on manganese dioxide nanoflowers (MnO2NFs) and zinc sulfide quantum dots (ZnSQDs) was constructed for the first time to sensitively detect procalcitonin (PCT) in human serum. rGO@Ag functioned not only to adsorb primary antibodies (Ab1) but also to improve the electrical conductivity of the immunosensor. The MnO2NFs and ZnSQDs in the nanocomposite, synergistically with silver nanoparticles, simultaneously functioned as cathodic ECL emitters to enhance the detection sensitivity of PCT by shortening the electron-transfer path, thereby reducing energy loss. Under the optimized experimental conditions, the ECL immunosensor was capable of quantitatively detecting PCT in the linear range of 0.1 pg mL-1 to 100 ng mL-1 and over the scanning potential range of -2.0-0 V, with a detection limit of 0.033 pg mL-1. Furthermore, the ECL immunosensor demonstrated high specificity for PCT in the presence of other competing antigens, excellent stability over 10 cycles, and excellent reproducibility, corroborating its potential for measuring PCT concentrations in clinical samples.

Information Detection and Data Denoising Method Using Nano Electrode Array Sensor

Computer technology and sensor technology can be combined. The technology set can be used to monitor the concentration of heavy metals in soil, which can help to prevent the occurrence of heavy metal pollution in time. First, nanotechnology, electrode polarization and the advantages of gold nanoparticles modified electrode are studied, and the design method of the nano electrode array is further analyzed. Also, the internal parameters of the three-electrode equivalent circuit are studied, and the model of the three-electrode equivalent circuit is derived. On this basis, a heavy metal monitoring circuit based on the nano electrode array sensor is designed. While the information monitoring based on this circuit is performed, wavelet domain denoising technology is studied in data processing. In view of the defects of the general hard threshold in practical application, the threshold is improved to recognize the depth of denoising. In the experiment, gold nanoparticles modified mercury electrode is used as working electrode. According to the principle that the precipitation time is inversely proportional to the detection current, 0.01 mol/L HCl is selected as the solution environment; moreover, it is set that pH=4 and the precipitation time is 4 min. The results show that for the same kind of ions, with the increase of the concentration of ions to be measured, the scanning potential range remains unchanged, while the peak current increases significantly. Metal ions can be effectively identified based on the potential corresponding to peak value. In the data processing of the detection circuit, the improved signal denoising method is compared with the default threshold wavelet domain denoising technology. The results show that the improved wavelet domain denoising method has less signal error, and the denoising effect of heavy metal detection is obvious.

Postsynthesis Ligand Exchange Induced Porphyrin Hybrid Crystalloid Reconstruction for Self-Enhanced Electrochemiluminescence.

In traditional coreactant electrochemiluminescence (ECL), the efficiency of the coreactant catalyzed into an active intermediate is one of the dominant factors restricting the luminous intensity. In this work, Co-2-MI-ZnTCPP is designed as a composite material integrating coreaction accelerator (Co-N) and luminophore. Through the catalytic effect of Co-N structures on hydrogen peroxide, the in situ generation and accumulation of active intermediates are achieved, which will react with porphyrin anion radical, thereby bringing out self-enhanced ECL. By adjusting the scanning potential range, the ECL mechanism is thoroughly studied and the contribution of each potential window to the luminescence is obtained. This work provides inspiration for the design of integrated ECL emitters with a coreaction accelerator and luminophore, providing a new way for the construction of a self-enhanced ECL emitter.

Perylene Diimide and Luminol as Potential-Resolved Electrochemiluminescence Nanoprobes for Dual Targets Immunoassay at Low Potential

In the field of clinical diagnosis, it is important to construct a potential-resolved multiplex electrochemiluminescence (ECL) biosensor for decreasing the false-positive rate and improving the diagnostic accuracy. However, the shortage of low-potential cathodic luminophores between -1 and 0 V (vs Ag/AgCl) severely limited the development of the biosensor. Herein, we synthesized a novel luminophore N,N-bis-(3-dimethyl aminopropyl)-3,4,9,10-perylene tetracarboxylic acid diimide (PDI), which gave dual emissions at -0.25/-0.26 V with K2S2O8 as a co-reactant in aqueous solution. The ECL was assigned to excited J-type PDI dimers. Then, PDI and luminol were used as luminophores to respectively combine with graphite oxide and gold nanoparticles and form potential-resolved ECL nanoprobes. Also, this potential-resolved ECL nanoprobes were respectively functionalized by secondary antibodies (Ab2) to construct a low-potential sandwiched ECL immunosensor for tumor markers carcinoembryonic antigen (CEA) and α-fetoprotein (AFP) simultaneous determination during linear scanning potential range from -0.6 to 0.6 V. The prepared multiplex immunosensor exhibited sensitive ECL response for CEA at -0.6 V due to PDI and that for AFP at 0.6 V due to luminol, and both linear semilogarithmical ranges were from 0.1 pg to 1 ng mL-1. In addition, PDI with dual ECL peaks showed enticing prospect of built-in self-calibration for a precise quantitative and bioimaging analysis.

ELECTRODEPOSITION AND CHARACTERIZATION OF HYDROXYAPATITE/CARBON NANOTUBES (HAp/CNTs) NANOCOMPOSITE ON 316L STAINLESS STEEL

Hydroxyapatite/carbon nanotubes (HAp/CNTs) nanocomposite was successfully synthesized as a coating on 316L stainless steel (316L SS) by electrodeposition technique. The effects of scanning potential range, scanning rate, number of scans, and synthesis temperature were investigated. Fourier Transform Infrared Spectroscopy (FT-IR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and mechanical test were performed to characterise of the coatings. Suitable condition to synthesize HAp/CNTs/316L SS coatings is a scanning potential range from 0 to -1.65 V/SCE, a scanning rate of 5 mV/s, 5 scans, an electrolyte temperature of 45 oC and a CNTs concentration of 0.5 g/L in the electrolyte solution. At the condition, obtained nanocomposite coatings are composed of HAp and CNTs with the coating thickness is equal to 6.9 µm. The presence of 0.5 g/L of CNTs in the electrolyte solution, the solubility of obtained coatings is lower than that of pure HAp coating. In addition, the hardness of the HAp/CNTs coatings reaches 5.6 GPa, which was nearly 25 % higher than that of pure HAp.

Novel Low Symmetric Alkyne Terminated Metallophthalocyanine Modified Electrode Via Click Chemistry for Electrochemical Determination of Mercury (II)

An electrochemical method for the determination of trace levels of mercury(II) ions using metallophthalocyanine (MPc) modified glassy carbon electrode (GCE) via click chemistry by differential pulse stripping voltammetry (DPSV) is described for the first time. In this report, the novel synthesized low symmetry alkyne terminated cobolt Phthalocyanine (CoPc) derivative was prepared and characterized using FTIR, MS, UV-Vis, Elemental Analysis and cyclic voltammetry. Operational parameters such as number of scan for grafting step, concentration of CoPc derivative for clicking solution, and scanning potential range were optimized. Under the optimum experimental conditions, the anodic peak current is proportional to the concentrations of mercury over a wide range of 0.1 to 0.8 mM with the lowest detectable concentration of 440 nM. The selectivity of the CoPc modified GCE via click chemistry towards mercury in the presence of potential interferents such as copper, lead, cadmium and zinc was well studied. The fabricated electrochemical sensor exhibited very good electrocatalytic properties such as good reproducibility, stability and is suitable for the detection of mercury in tap water and seawater. Figure 1

From banana stem to conductive paper: A capacitive electrode and gas sensor

A capacitive, conductive and methanol sensor composite have been prepared by a simple process of acid hydrolysis, using potential cellulose source extracted from a residue of banana stem. The material was hydrolyzed with sulphuric acid in the presence of carboxylated multiwalled carbon nanotubes (MWCNTs) to promoted chemical interaction among cellulose and carbon surface. With these material was prepared a paper film used to design an electrode. The cellulose/MWCNT composite was investigated using x-ray diffraction, nuclear magnetic resonance, infrared spectroscopy, transmission electron microscopy and size measurement. The electrical properties were evaluated by cyclic voltammetry, impedance spectroscopy, charge/discharge testing and simulation in an equivalent circuit. The gas sensor property was evaluated by an experimental apparatus, measuring the electric current front exposure the electrode to different concentrations of methanol in different temperatures. The cellulose/MWCNT electrode displays a strong dependence of a scan rate and potential range in capacitive properties. The chemical interaction archived between MWCNT and cellulose is relevant to develop a flexible cellulose composite, with specific capacitance of 3,08mF/cm2 as functional nanotube integration. The flexible electrode developed in this study would be the ideal matrix to anchorage sensitive molecules and particles on specific applications like biosensor or electronic device.

Polyaniline/Gold Composites for Electrochemical and Optical Biosensing

Development of robust biosensors for on-line/in-line detection would enable continuous monitoring and control of process parameters in pharmaceutical manufacturing and new approaches for medical diagnostics and bioterrorism security. Key attributes of such biosensors are facile fabrication, reproducibility, high sensitivity and selectivity. Electrochemical (EC) detection provides a simple transduction mechanism, converting oxidation and reduction of the target analyte or electrochemical tag into an electrical signal. The equipment necessary for EC detection can be made small, portable and also combined with the electrode array on a single chip using lithographic techniques. Important additional information regarding the identity of an analyte can be obtained from optical techniques, specifically, surface enhanced Raman spectroscopy (SERS). Therefore, we have worked to develop a bi-modal approach, utilizing simultaneous EC and SERS techniques, to enhance a sensor’s figures of merit and its reliability in critical applications. When used in tandem, this bi-modal EC-SERS approach can provide information about electrochemical activity and molecule-specific vibrational signatures.It is also interesting to note that while EC methods measure an averaged property of the entire surface, SERS can measure the vibrational modes of molecules on a small segment on the surface. Thus, together these methods can provide site-specific and averaged information simultaneously and in real-time. In biosensing applications, the ability to uncouple the behavior of a few molecules, or even a single molecule, from the ensemble average can provide much needed insight into fundamental biochemical processes.An EC-SERS surface must have sufficient conductivity to act as an electrode, selectively bind the target analyte and have the hot-spots required for enhancement of the Raman signal. Our surface is based on electrochemically deposited polyaniline (PANI) which is subsequently used as a template for controlled gold nanoparticle (Au-NP) growth leading to PANI/Au-NP composites with tunable electrochemical and SERS properties. PANI was chosen because of its rich EC behavior and its ability to spontaneously bind and reduce potassium chloroaurate to metallic gold. The facile deposition procedure is well-suited for applications in biosensing via the EC-SERS bi-modal technique.The film deposition and ongoing optimization of EC-SERS responses are carried out with an in-house fabricated electrode array and flow-cell for precise control over solution composition and electrical potential. The electrode array consists of 16 individually addressable platinum disc electrodes with diameter of 1 mm. We discuss the efficient examination of a complex, cross-correlated parameter space for these bi-modal biosensor devices, which includes; film thickness, morphology, and nanoparticle size and density.The fabrication procedure is illustrated in figure 1. First, PANI is grown on platinum electrodes by oxidative electropolymerization of aniline from a diluted HBF4, HCl or a similar acidic solution. The choice of acid, particularly the anion, plays a large role on the morphology and electrochemical properties of the grown film. The electrochemical method used for deposition; i.e. cyclic voltammetry, constant current, or constant potential, as well as scan rate, potential range, and total charge, are also important for tuning the characteristics of the grown film. Most importantly, these parameters affect the subsequent growth of Au-NPs in the film.The growth of Au-NPs (step 2) is initiated spontaneously by exposing the PANI electrode to chloroaurate while controlling the electrode potential. In addition to the previously mentioned deposition parameters, the immersion time in the Au salt solution and its concentration are key to controlling the size and density of the NPs. In addition to electrochemical measurements the PANI/Au-NPs are analyzed using optical microscopy, SEM and XPS. The Au-NPs are distributed mostly on the surface of the polymer where they are open to solution and available for further functionalization, for instance by thiol groups, to be used for biomolecule immobilization in step 3.

Electrochemical fabrication of a novel polycarbazole coating for the headspace solid‐phase microextraction and GC determination of some chlorobenzenes

A novel polycarbazole coating was prepared by cyclic voltammetry on a platinum wire. The solution for electropolymerization contained N,N-dimethylformamide, propylene carbonate (v/v = 1:9), 0.10 M carbazole and 0.10 M tetrabutylammonium perchlorate; the cyclic scan potential range was 0.8-2.0 V (versus Ag/AgCl). The resulting polycarbazole coating showed a porous structure and had a large specific surface area. When it was used for the headspace solid-phase microextraction of chlorobenzenes (i.e. chlorobenzene, 2-chlorotoluene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,2,4-trichlorobenzene) followed by GC analysis, it presented excellent analytical performance. Under the optimized conditions the linear ranges were 0.25-250 μg/L with correlation coefficients >0.985, and the low detection limits were 15-61 ng/L (S/N = 3) for different chlorobenzenes. The RSDs were 2.4-4.9% for five successive measurements with a single fiber, and for fiber-to-fiber they were 6.3-13.1% (n = 5). Furthermore, the polycarbazole coating displayed good thermal stability (>350°C) and durability (more than 250 times). The proposed method was successfully applied to the extraction and determination of chlorobenzenes in waste water and lake water, and the recoveries for standards added were 86-114% for different analytes.

Electrodeposited Pd–MoOx catalysts with enhanced catalytic activity for formic acid electrooxidation

Pd–MoOx catalysts supported on glassy carbon electrode were co-deposited using cyclic voltammetry. The influence of two key deposition parameters (i.e. scanning potential range and concentration of sodium molybdate in the electrolyte) on the catalysts was investigated by X-ray diffraction, energy dispersive X-ray spectroscopy, element analysis mapping, scanning electron microscopy, X-ray photoelectron spectroscopy and typical electrochemical measurements, respectively. It was found both of the parameters had great effect on the morphology, chemical states, composition and electrochemical performance of the catalysts. By tuning the electrodeposition parameters, we found the optimal condition to prepare the catalysts. The as-prepared catalysts showed much improved catalytic activity and stability for formic acid electrooxidation. The enhanced performance can be attributed to the fine porous structure composed of small particles, hydrogen spillover effect and unique element distribution (different composition between surface and bulk).

Evaluation of solid-phase microextraction using a polythiophene film and liquid chromatography with spectrophotometric detection for the determination of antidepressants in plasma samples

Polythiophene (PTh) phase electropolymerized on the stainless steel wire was evaluated as solid-phase microextraction (SPME), and analysis by liquid chromatography with spectrophotometric detection (LC-UV) for determination of new-generation antidepressants, selective serotonin reuptake inhibitors (SSRIs) (citalopram, paroxetine, fluoxetine and sertraline), in plasma samples. The influence of electropolymerization variables (scan rate, potential range and scan cycles) was evaluated on SPME performance. The SPME variables (extraction time, temperature, matrix pH, ionic strength and desorption procedure), as well as the influence of plasma proteins on sorption mechanisms were also evaluated. The SPME/LC-UV method developed for determination of antidepressants in plasma sample presented a linear range between the limit of quantification (LOQ, 200-250 ng mL-1) to 4000 ng mL-1, and interday precision with coefficient of variation (CV) ranged from 11 to 15%. The proposed method can be a useful tool for the determination of antidepressants in human plasma samples in urgent toxicological analysis after the accidental or suicidal intake of higher doses of medications.

Electrocatalytic Oxidation of Ascorbic Acid Using a Poly(aniline-co-m-ferrocenylaniline) Modified Glassy Carbon Electrode

A poly(aniline-co-m-ferrocenylaniline) was successfully synthesized on a glassy carbon electrode (GCE) by electrochemical copolymerization using a scan potential range from −0.3 to +0.9 V (vs. Ag/AgCl) in 0.5 M H2SO4 containing 30% acetonitrile (ACN), 0.1 M aniline (Ani) and 0.005 M m-ferrocenyaniline (m-FcAni). The field emission scanning electron microscope (FESEM) and electrochemical methods were used to characterize the poly(Ani-co-m-FcAni) modified electrode. The poly(Ani-co-m-FcAni)/GCE exhibited excellent electrocatalytic oxidation of ascorbic acid (AA) in citrate buffer solution (CBS, pH 5.0). The anodic peak potential of AA was shifted from +0.55 V at the bare GCE to +0.25 V at the poly(Ani-co-m-FcAni)/GCE with higher current responses than those seen on the bare GCE. The scan number at the 10th cycle was selected as the maximum scan cycle in electrochemical polymerization. The limit of detection (LOD) was estimated to be 2.0 μM based on the signal-to-noise ratio (S/N = 3). The amperometric responses demonstrated an excellent selectivity for AA determination over glucose (Glu) and dopamine (DA).

Almost completely dedoped electrochemically deposited luminescent films exhibiting excellent LED performance

An improved method for electrochemical deposition (ED) of a novel precursor (peripheral carbazole substituted 9,9′-spirobifluorene (TCPC)) for fabricating highly efficient luminescent films and devices has been developed. Electrochemical deposition often leaves residual charged ion species within the film. These species can negatively impact the performance of these films in OLED applications. The amount of residual charged species in the films can be reduced by controlling the oxidation and reduction potentials, by using electrolytes with different counter anions, and by washing with solvents. An optimized ED process showed a significant decrease in the doping level; up to 0.07% in ED film. The films prepared under a scan potential range from 0.85 to −0.8 V, using TBAAsF 6 as the supporting electrolyte, and washed with solvent mixtures of acetonitrile and CH 2Cl 2 ( V/ V = 2/3) demonstrated excellent device performance. Light-emitting devices fabricated by electrochemical deposition achieved deep blue emission ( x, y) = (0.16, 0.06) in CIE coordinates. High luminance efficiencies of 2.3 cd A −1 were achieved for single-layer device; luminescence efficiencies of 4.4 cd A −1 were achieved for a double-layer device. Finally, the problem that ED films usually exhibit low electroluminescent efficiency is solved.

Electrochemical studies on the interaction of heparin with crystal violet and its analytical application

In this paper, crystal violet (CV) was used to determine heparin concentration by linear sweep voltammetry on a dropping mercury electrode (DME). In Britton-Robinson (B-R) buffer solution, pH 3.0, CV had a well-defined second-order derivative linear sweep voltammetric reductive wave at −0.74 V (vs. SCE). After the addition of heparin to the CV solution, the reductive peak current decreased greatly with the positive movement of the peak potential and without appearance of new peaks in the scanning potential range. Based on the decrease in the reductive peak current, a new voltammetric method for the determination of heparin was established. The conditions for the interaction and the electrochemical detection were optimized, and interfering substances were investigated. Under the optimal conditions, the decrease in reductive peak currents of CV was proportional to heparin concentration in the range 0.1–8.0 mg/L with the linear regression equation Δip″(nA) = 400.42 + 1563.11c (mg/L), (n = 14, γ = 0.993). The detection limit was 0.092 mg/L. This new method was further successfully applied to the determination of heparin content in heparin sodium injection samples with satisfactory results. The binding ratio and binding mechanism were also studied by the electrochemical method.

Electrochemical copolymerization of aniline with m-aminophenol and novel electrical properties of the copolymer in the wide pH range

A copolymer, poly(aniline- co-m-aminophenol), has been synthesized using repeated potential cycling. The monomer concentration ratio, acid concentration and applied potential strongly affect the copolymerization rate and the properties of the copolymer. The optimum conditions for the copolymerization are that the scan potential range is controlled between −0.10 and 0.95 V (vs.SCE), and a solution consists of 0.34 M aniline, 0.012 M m-aminophenol and 2 M H 2SO 4. The IR spectra of the copolymers demonstrate that the m-aminophenol units are included in the copolymer chains. The cyclic voltammograms of the copolymers in 0.3 M Na 2SO 4 solution with various pH values were performed at the potential ranges from −0.20 to 0.80 V and at a scan rate of 60 mV s −1. The results indicate that the copolymer still hold 41.7% of the electrochemical activity when the copolymer electrode was transferred from a solution of pH 5.0 to a solution of pH 11.0 in the potential range of −0.20 to 0.80 V. An impedance plot of the copolymer in a solution with pH 12.0 and at 0.40 V is constructed of a semicircle and a Warburg line with a slope of 1. This means that the electrode reaction of the copolymer at pH 12.0 is also under mass transfer control. The conductivity of the copolymer prepared under the optimum conditions is 1.42 S cm −1, and slightly depends on the pH value. Thus, the pH dependence of the electrical properties of the copolymer is improved compared with poly(aniline- co-o-aminophenol), and is much better than that of the parent polyaniline.

Linear Sweep Voltammetric Determination of Heparin Based on Its Interaction with Neutral Red

In this article the interaction of neutral red with heparin was characterized by linear sweep voltammetry on the hanging mercury drop electrode (HMDE) and further used for the determination of heparin. In pH 1.5 Britton‐Robinson (B‐R) buffer solution, neutral red (NR) has a well‐defined second‐order derivative linear sweep voltammetric reductive wave at −0.24 V (vs. SCE). After the addition of heparin into the NR solution, the reductive peak current decreases without the movement of the peak potential and the appearances of new peaks in the scanning potential range. Based on the decrease of the reductive peak current, a new voltammetric method for the determination of heparin is established. The conditions for the interaction and the electrochemical detection are optimized, and the interference substances for detection are investigated. Under the optimal conditions, the decrease of reductive peak current of NR is proportional to heparin concentration in the range of 2.0–10.0 mg/L with the linear regression equation as Δip″(nA)=−172.03+71.49C (mg/L), (n=9, γ=0.997) and the detection limit is 1.34 mg/L. This new method is further successfully applied to the determination of heparin in heparin injection samples with satisfactory results. The binding ratio and binding mechanism of NR with heparin are also discussed. Supported by Natural Science Foundation of Qingdao City (04‐2‐JZ‐114), China Postdoctoral Science Foundation (No. 2003033492), and the National Natural Science Foundation of China (No. 20375020).