Stripping voltammetric determination of silver(I) at carbon paste electrode modified with 3-amino-2-mercapto quinazolin-4(3H)-one

A differential pulse anodic stripping voltammetric method was developed for the determination of Ag(I) at a 3-amino-2-mercapto quinazolin-4(3H)-one modified carbon paste electrode. The analysis procedure consisted of an open circuit accumulation step in stirred sample solution for 12 min. This was followed by medium exchange to a clean solution where the accumulated Ag(I) was reduced for 15 s in −0.6 V. Subsequently an anodic potential scan was effected from −0.2 to +0.2 V to obtain the voltammetric peak. The detection limit of silver(I) was 0.4 μg L⁻¹ and R.S.D. for 10, 100 and 200 μg L⁻¹ silver(I) were 2.4, 1.8 and 1.3%, respectively. The calibration curve was linear for 0.9-300 μg L⁻¹ silver(I). Many coexisting ions had little or no effect on the determination of silver(I). The procedure was applied to determination of silver(I) in X-ray photographic films and natural waters. In X-ray photographic film samples, the results have compared to those obtained by atomic absorption spectroscopy.     

A highly selective fluorescent sensor for Cu based on 2-(2′-hydroxyphenyl)benzoxazole in a poly(vinyl chloride) matrix

This paper describes a copper selective optical chemical sensor based on static quenching of the fluorescence of 2-(2′-hydroxyphenyl)benzoxazole entrapped in a poly(vinyl chloride) (PVC) membrane. The effect of the composition of the sensing membrane was studied, and experimental conditions were optimized. The sensors exhibit stable response over the concentration range from 4.0 × 10⁻⁸ M to 5.0 × 10⁻⁵ M Cu²⁺ at pH 4.0-6.5, and a high selectivity. The response time for Cu²⁺ with concentration ≤5 × 10⁻⁶ M is less than 7 min. The optode can be regenerated using 0.1 M HCl and acetate buffer solution. The sensor has been used for direct measurement of copper content in river water samples with a relative error less than 4% with reference to that obtained by atomic absorption spectrometry.     

A new Cu(II)-5-(4-sulphophenylazo)-8-aminoquinoline complex used for copper determination in presence of gold and silver in water and mineral samples

In this work, a characterization of reagent chromophere 5-(4-sulphophenylazo)-8-aminoquinoline [SPA] by IR and ¹H RMN was carried out and a pK_a value of 3.55 ± 0.03 was found as well. An 1:2 stoichiometry for the Cu(II)-SPA complex was determined at pH 9 by Job and molar ratio methods. A value of 1.4 × 10¹⁴ for the stability constant was also found. Based on the formation of this complex a new method for the copper determination in presence of gold and silver was developed by derivative spectrophotometry using a previous preconcentration on solid phase. In this method, the analytical measures were executed directly in the solid phase containing the complex. The Cu(II) reacts with the reagent chromophere SPA previously retained in the anionic exchange DEAE Sephadex A25. In this determination, the first derivative at 605 nm was used. The quantification range was between (3.2 ± 0.3 × 10⁻¹) × 10⁻⁸ and (94.4 ± 0.9) × 10⁻⁸ mol L⁻¹ (3.2 ± 0.3 × 10⁻¹) × 10⁻⁸ , and (94.4 ± 0.9) × 10⁻⁸ mol L⁻¹. The repeatability expressed as RSD was between 1.1 and 2.0%. The method was applied successfully for the copper determination in mineral residuals and natural water samples. The results were consistent with those provided by ICP-mass spectrometry.     

The use of sublimable chlorotricarbonyl bis(phenylimino)acenaphthene rhenium(I) complexes as photosensitizers in bulk-heterojunction photovoltaic devices

A series of sublimable substituted chlorotricarbonyl bis(phenylimino)acenaphthene rhenium(I) complexes was synthesized and used in the fabrication of photovoltaic devices. The hole and electron carrier mobilities of these complexes are in the order of 10⁻³ to 10⁻⁴ cm² V⁻¹ s⁻¹. Heterojunction devices with CuPc/complex/C₆₀ (CuPc = copper phthalocyanine) as the active layer and bulk heterojunction devices with complex:C₆₀ as the active layer were fabricated. The rhenium complexes function as photosensitizer in the devices, and exhibit optical absorption in the region between 500 and 550 nm within which other components in the device do not absorb. Other devices with hole transport materials, exciton blocking materials, and different active layer thickness were also fabricated. Variation of substitution groups in the ligand did not show significant difference in device performance. The best power conversion efficiency of the devices was measured to be 1.29% under illumination of AM1.5 simulated solar light.     

Spectrophotometric determination of iron(III)-dimethyldithiocarbamate (ferbam) using 9-(4-carboxyphenyl)-2,3,7-trihydroxyl-6-fluorone

A spectrophotometric method was developed for the determination of iron(III)-dimethyldithiocarbamate (ferbam) by concerting it into an iron(III)-9-(4-carboxyphenyl)-2,3,7-trihydroxyl-6-fluorone complex. In NH₃-HAc buffer solution (pH 6.5), the reagent reacts with ferbam to form a blue complex with a maximum absorption peak at 640 nm. The reaction can be completed rapidly at room temperature and the absorbance is stable for at least 24 h. The apparent molar absorption coefficient, Sandell’s sensitivity of the complex, the detection limit and the relative standard deviation were found to be 1.06×10⁵ l mol⁻¹ cm⁻¹, 3.9 ng cm⁻², 2.2 ng ml⁻¹ and 1.06%, respectively. From 0 to 75 μg of ferbam in 25 ml solution the absorbance obeyed Beer’s law. The effect of foreign ions and other dithiocarbamates were also studied in detail. The results indicated that all coexisting ions examined can be tolerated in considerable amounts, especially other dithiocarbamates such as ziram and zineb, which always interfere with the determination of ferbam in the literature. The proposed method is very sensitive, selective and simple, it has been applied to determine ferbam in commercial samples.     

p-Dimethylaminobenzaldehyde thiosemicarbazone: a simple novel selective and sensitive fluorescent sensor for mercury(II) in aqueous solution

A novel and simple fluorophore, p-dimethylaminobenzaldehyde thiosemicarbazone (DMABTS), was prepared in order to find available fluorescent chemosensor for mercuric ion in aquesous solution. DMABTS emitted fluorescence at 448 nm in aqueous solution and its fluorescence intensity was completely quenched upon interaction with Hg²⁺ ions, which should be attributed to the 1:1 complex formation between DMABTS and Hg²⁺. The binding constant of the complex was determined as 7.48 × 10⁶ mol l⁻¹. The linear range of quantitative detection of 0 to 5.77 × 10⁻⁶ mol l⁻¹ and the detection limit of 7.7 × 10⁻⁷ mol l⁻¹ for Hg²⁺ in the 6.3 × 10⁻⁶ mol l⁻¹ DMABTS aqueous solution were obtained from a calibration curve. The coexistence of several transition metal ions and anions did interfere the fluorometric titration of Hg²⁺ ion by less than 4% in the emission change.     

Chromium(III) complexes bearing 2-benzoxazolyl-6-arylimino-pyridines: Synthesis and their ethylene reactivity

A series of chromium(III) complexes bearing 2-benzoxazolyl-6-aryliminopyridines was synthesized and characterized by IR spectroscopic and CHN analysis. The X-ray crystallographic analysis of complex Cr3 revealed a distorted octahedral geometry. When activated by Et₂AlCl, MAO or MMAO, these chromium complexes exhibited activities towards ethylene reactivity. High activities of ethylene oligomerization (up to 9.19 × 10⁶ g mol⁻¹ (Cr) h⁻¹) were observed in the catalytic system using MMAO as a cocatalyst, meanwhile good activities of ethylene polymerization were achieved (up to 5.20 × 10⁵ g mol⁻¹ (Cr) h⁻¹) by using MAO as a cocatalyst. Various reaction parameters were investigated in detail, and the steric and electronic effects of ligands were discussed.     

Band gap tunable for near-infrared absorbing chromophores with multi-triphenylamine and tris (thieno)hexaazatriphenylenes acceptors

Two disk-like D-A type chromophores with multi-triphenylamine donors and hexaazatriphenylenes acceptors were synthesized and fully characterized by ¹H and ¹³C NMR, elemental analysis and mass spectrometry. The effects of the hexaazatriphenylene on the optical and electrochemical properties and band gap of the chromophores were investigated. As the hexaazatriphenylene core fused with three thiophene rings, the band gaps of the compounds could be tuned from 1.65 eV to 1.15 eV. The π-π* absorption peak and charge-transfer absorption peak of the hexaazatriphenylene compounds were red shifted from visible spectrum region (393 and 530 nm) to near-infrared spectrum region (542 and 756 nm). In addition, due to an increase in the π electronic coupling between electron donor and electron acceptor, the extinction coefficient (charge-transfer absorption) of the hexaazatriphenylene compound decreases 85% from 3.4 × 10⁴ mol⁻¹ dm⁻³ cm⁻¹ to 0.5 × 10⁴ mol⁻¹ dm⁻³ cm⁻¹.     

Simultaneous determination of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) in food samples using a carbon composite electrode modified with Cu3(PO4)2 immobilized in polyester resin

A simple electrochemical method was developed for the single and simultaneous determination of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) in food samples using square-wave voltammetry (SWV). A carbon composite electrode modified (MCCE) with copper (II) phosphate immobilized in a polyester resin was proposed. The modified electrode allowed the detection of BHA and BHT at potentials lower than those observed at unmodified electrodes. A separation of about 430 mV between the peak oxidation potentials of BHA and BHT in binary mixtures was obtained. The calibration curves for the simultaneous determination of BHA and BHT demonstrated an excellent linear response in the range from 3.4 × 10⁻⁷ to 4.1 × 10⁻⁵ mol L⁻¹ for both compounds. The detection limits for the simultaneous determination of BHA and BHT were 7.2 × 10⁻⁸ and 9.3 × 10⁻⁸ mol L⁻¹, respectively. In addition, the stability and repeatability of the electrode were determined. The proposed method was successfully applied in the simultaneous determination of BHA and BHT in several food samples, and the results obtained were found to be similar to those obtained using the high performance liquid chromatography method with agreement at 95% confidence level.     

Spectrofluorimetric study of the interaction of copper(II) and bis-heterocyclictriazene reagent in the presence of beta-cyclodextrin

A new reagent, 1,3-bis(2-benzothiazolyl-diazoamino)benzene (BBTAB), was first synthesized and characterized by elemental analysis, ¹H NMR and IR spectra. The inclusion complex of BBTAB with β-cyclodextrin (β-CD) was formed. BBTAB in the inclusion complex or alone reacts with copper(II) to form chelate complex in a slight basic medium, which results in drastic or slight fluorescence enhancement, respectively. The spectrofluorimetric method of trace amount of copper(II) based on the enhancement of inclusion complex by binding with copper(II) was established. The excitation and emission wavelengths of the BBTAB/β-CD/Cu system are 389 and 480 nm, respectively. Under optimal conditions, a linear response of BBTAB/β-CD to copper(II) is obtained in the range of 3.0 × 10⁻⁷ to 1.0 × 10⁻⁵ mol L⁻¹, and the detection limit is determined to be 1.2 × 10⁻⁸ mol L⁻¹. The method is selective, sensitive and simple, and has been used for the determination of trace copper(II) in water samples with satisfactory results. The possible response mechanism of BBTAB/β-CD or BBTAB to copper(II) and the role of β-CD in the drastic enhancement of fluorescence of BBTAB/β-CD/Cu system have been discussed.     

Preliminary evaluation of monolithic column high-performance liquid chromatography with tris(2,2′-bipyridyl)ruthenium(II) chemiluminescence detection for the determination of quetiapine in human body fluids

High-performance liquid chromatography (HPLC) with tris(2,2′-bipyridyl)ruthenium(II) chemiluminescence detection methodology is reported for the determination of the atypical antipsychotic drug quetiapine and the observation of its major active and inactive metabolites in human urine and serum. The method uses a monolithic chromatographic column allowing high flow rates of 3 mL min⁻¹ enabling rapid quantification. Flow injection analysis (FIA) with tris(2,2′-bipyridyl)ruthenium(II) chemiluminescence detection and HPLC time of flight mass spectrometry (TOF-MS) were used for the determination of quetiapine in a pharmaceutical preparation to establish its suitability as a calibration standard. The limit of detection achieved with FIA was 2 × 10⁻¹¹ mol L⁻¹ in simple aqueous solution. The limits of detection achieved with HPLC were 7 × 10⁻⁸ and 2 × 10⁻¹⁰ mol L⁻¹ in urine and serum, respectively. The calibration range for FIA was between 5 × 10⁻⁹ and 1 × 10⁻⁶ mol L⁻¹. The calibration ranges for HPLC were between 1 × 10⁻⁷-1 × 10⁻⁴ and 1 × 10⁻⁸-1 × 10⁻⁴ mol L⁻¹ in urine and serum, respectively. The quetiapine concentrations in patient samples were found to be 3 × 10⁻⁶ mol L⁻¹ in urine and 7 × 10⁻⁷ mol L⁻¹ in serum. Without the need for preconcentration, the HPLC detection limits compared favourably with those in previously published methodologies. The metabolites were identified using HPLC-TOF-MS.     

Tris(2,2'-bipyridyl)ruthenium(II)-Zirconia-Nafion composite modified electrode applied as solid-state electrochemiluminescence detector on electrophoretic microchip for detection of pharmaceuticals of tramadol, lidocaine and ofloxacin

Tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺)-Zirconia-Nafion composite modified glassy carbon disk electrode as a solid-state electrochemiluminescence (ECL) detector is successfully applied to an electrophoretic microchip system with a wall-jet configuration. Pharmaceuticals such as tramadol, lidocaine and ofloxacin were selected to characterize the performance of this microchip capillary electrophoresis (CE)-ECL detection system. Voltammetric and ECL behaviors of immobilized Ru(bpy)₃²⁺ were investigated in lidocaine system. Influences of the separation electric field to cyclic voltammograms (CVs) of the immobilized Ru(bpy)₃²⁺ were also investigated. Tramadol, lidocaine and ofloxacin can be baseline separated without any additives. The detection limits (S/N = 3) were 2.5 × 10⁻⁵ mol L⁻¹ for tramadol, 5.0 × 10⁻⁶ mol L⁻¹ for lidocaine, 1.0 × 10⁻⁵ mol L⁻¹ for ofloxacin under the sample injection of picoliters, and the linear ranges were from 5.0 × 10⁻⁵ to 2.5 × 10⁻³ mol L⁻¹ for tramadol, 1.0 × 10⁻⁵ to 1.0 × 10⁻³ mol L⁻¹ for lidocaine, and 1.0 × 10⁻⁵ to 2.5 × 10⁻³ mol L⁻¹ for ofloxacin, respectively.     

Investigation on enhanced chemiluminescence reaction systems with bis(hydrogenperiodato) argentate(III) complex anion for fluoroquinolones synthetic antibiotics

A novel chemiluminescence (CL) reaction system with bis(hydrogenperiodato) argentate(III) complex anion (Ag(III) complex, [Ag(HIO₆)₂]⁵⁻), for the first time, is developed for the determination of lomefloxacin (LMFX), enrofloxacin (ENLX) and pefloxacin (PFLX). The possible CL emission mechanism was discussed by comparing the fluorescence emission with CL spectra. The CL conditions of [Ag(HIO₆)₂]⁵⁻-H₂SO₄-LMFX/ENLX/PFLX systems were investigated and optimized. Under the optimized experimental conditions, the CL intensity is proportional to the concentration of the drugs in the range 0.2994-36.80 × 10⁻⁷ g mL⁻¹ for LMFX, 4.00-30.0 × 10⁻⁷ g mL⁻¹ for ENLX and 1.54-27.64 × 10⁻⁷ g mL⁻¹ for PFLX. The limit of detection (s/n = 3) was 9.1 × 10⁻⁹ g mL⁻¹ for LMFX, 3.1 × 10⁻⁹ g mL⁻¹ for ENLX and 4.4 × 10⁻⁹ g mL⁻¹ for PFLX. The recovery of LMFX, ENLX and PELX from the spiked pharmaceutical preparations was in the range of 92.3-105% with the RSDs of 0.5-2.7%. For urine, serum and milk samples the recoveries of the three drugs were in the range of 85.1-107% for LMFX with the RSDs of 2.3-3.4%. 80.2-112% for ENLX with the RSDs of 1.4-2.8%, and 87.8-114% for PFLX with the RSDs of 1.6-2.7%. The proposed method was applied successfully to the determination of these compounds in real samples.     

Synthesis,characterization and ethylene oligomerization and polymerization of 2-(1H-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridylchromium chlorides

A series of N^N^N tridentate chromium complexes (C1–C6) bearing 2-(1H-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridine derivatives was synthesized and characterized by elemental and spectroscopic analysis along with single-crystal X-ray crystallography. X-ray crystallographic analyses reveal chromium complex C1 as a distorted six-coordinated octahedral geometry. On treatment with modified methylaluminoxane (MMAO), the chromium complexes exhibited high activities for ethylene oligomerization (up to 1.50 × 10⁶ g mol⁻¹ (Cr) h⁻¹) and polymerization (up to 2.06 × 10⁶ g mol⁻¹ (Cr) h⁻¹) at 10 atm ethylene pressure. Various reaction parameters were investigated in detail, and less steric hindrance and electron-withdrawing substituents of ligands enhance the catalytic activities of their chromium complexes.     

Preparation of poly(vinylpyrrolidone)-protected Prussian blue nanoparticles-modified electrode and its electrocatalytic reduction for hemoglobin

In this paper, a novel modified electrode was developed by using highly dispersed Prussian blue (PB) nanoparticles protected by poly(vinylpyrrolidone) (PVP). The size of the nanoparticles was controlled through adjusting the feed ratio of PVP/Fe²⁺. Physical characteristics of the nanocomposite were studied by transmission electron microscopy (TEM), UV-vis, IR spectroscopy, and X-ray powder diffraction (XRPD) analysis. The electrocatalytic reduction of hemoglobin (Hb) at PVP-protected PB nanoparticles (PVP/PB NPs)-modified electrode had been investigated. In addition, the size effects and biocompatibility of PVP/PB NPs for the electrochemistry of Hb were also observed. Experimental results indicated that the reduction peak currents of Hb were linear with its concentrations over the range from 1.0 × 10⁻⁷ to 1.2 × 10⁻⁵ mol/L and the calculated detection limit (S/N = 3) was 4.0 × 10⁻⁸ mol/L.     

Mn(II)-sodium dodecyl sulphate complex mimic enzyme-catalyzed fluorescence quenching of Pyronine B by hydrogen peroxide

Mn(II)-sodium dodecyl sulphate complex (Mn(II)-SDS) is used to mimic the active group of peroxidase. The catalytic characteristic of this mimic enzyme catalyst in the oxidation reaction of fluorescence substrate, tetraethyldiaminoxanthyl chloride (Pyronine B (PB)), with hydrogen peroxide has been studied. The experimental results show that Mn(II)-SDS complex has similar catalytic activity that of peroxidase. The steady-state catalytic rate depends upon mimic enzyme and substrate concentrations, and the Michaelis-Menten parameters K_m, V_max and K_cat are 7.6×10⁻⁶ M, 7.9×10⁻⁷ M s⁻¹ and 7.9 s⁻¹, respectively. The catalytic activity of Mn(II)-SDS complex is compared with those of HRP and Hemin. Though the catalytic activity of Mn(II)-SDS complex is 15.9% of that of HRP, it can catalyze the oxidation reaction of PB with hydrogen peroxide lead to fluorescence quenching of PB. Under optimum conditions, linear relationship between fluorescence quenching F₀/F and concentration of H₂O₂ is in the range of (0.0-3.6) × 10⁻⁷ M. The detection limit is determined to be 3.0×10⁻⁹ M. By coupling this mimic catalytic reaction with the catalytic reaction of glucose oxidase (GOD), glucose can be detected. Linear relationship between F₀/F and concentration of glucose is in the range of (0.0-1.4) × 10⁻⁷ M. The detection limit is determined to be 4.2×10⁻⁹ M. This method is applied to the determination of glucose in human serum and the results are in good agreement with the phenol-4-aminoantipyrine (4-AAP).     

Interaction between quercetin-copper(II) complex and DNA with the use of the Neutral Red dye fluorophor probe

The interaction of quercetin-Cu(II) complex with calf thymus DNA was investigated with the use of Neutral Red (NR) dye as a spectral probe by the application of UV-vis spectrophotometry, cyclic voltammetry and synchronous fluorescence spectroscopy. The results showed that both quercetin-Cu(II) complex and the NR molecule can intercalate into the double helix of the DNA. The 2:1 quercetin:Cu(II) complex (estimated binding constant = 2.85 × 10⁹) is stabilized by intercalation in the DNA (binding constant, K_{[quercetin-Cu(II)-DNA]} = (1.82 ± 0.20) × 10⁵ M⁻¹), and displaces the NR dye from the NR-DNA complex in a competitive reaction. Cyclic voltammetry studies confirm the intercalation reaction and show that the ratio (K_R/K_O) of binding constants for the reduced and oxidized forms of the metal complex is 2.05. Furthermore, the alternative least squares (ALS) method was applied to resolve a complex two-way array of the absorption spectra data. This yielded the equilibrium concentration profiles of each component in the reaction (NR, NR-DNA and quercetin-Cu(II)) as well as the corresponding pure spectra. The extracted profiles showed that at equilibrium the [NR-DNA] and [NR] trends decreased and increased symmetrically, respectively, with approximately linear behaviour being observed below 10 × 10⁻⁶ mol L⁻¹ of the added quercetin-Cu²⁺ complex. Thereafter, these trends converged asymptotically. The free [quercetin-Cu(II)] trend-line at equilibrium was linear over the whole range of the complex added. It was possible to estimate the approximate value of the equilibrium constant of the exchange process (approximately 5 × 10⁻¹) involving the intercalation of the quercetin-Cu(II) complex. It was also found that about 35% of the bound complex was unaccounted by the intercalation reaction, presumably being stabilized at an alternative site.     

Determination of adrenaline by using inhibited Ru(bpy)3 electrochemiluminescence

Adrenaline was found to inhibit strongly the electrochemiluminescence (ECL) from the Ru(bpy)₃²⁺/tripropylamine system when a working Pt electrode was maintained at 1.05 V (versus Ag/AgCl) in pH 8.0 phosphate buffer. On this basis, a flow injection (FI) procedure with inhibited electrochemiluminescence detection has been developed for determination of adrenaline. The method exhibited a good reproducibility, sensitivity, and stability with a detection limit (signal-to-noise ratio = 3) of 7.0×10⁻⁹ mol l⁻¹ and dynamic concentration range of 2×10⁻⁸ to 1×10⁻⁴ mol l⁻¹. The relative standard deviation was 2.2% for 1.0×10⁻⁶ mol l⁻¹ adrenaline (n=11). The method was successfully applied to the determination of adrenaline in pharmaceutical samples. Moreover, ECL emission spectra, UV-Vis absorption spectra and cyclic voltammograms of Ru(bpy)₃²⁺/tripropylamine/adrenaline were studied. The inhibition mechanism has been proposed as the interaction of electrogenerated Ru(bpy)₃^2+* and the o-benzoquinone derivatives, adrenochrome and adrenalinequinone, at the electrode surface.