Indigo chemiluminescence

Indigotin in basic solutions of polar aprotic solvents reacts with atmospheric oxygen yielding isatin. The reaction is accompanied by emission of light with a quantum yield equal to 2.6×10^?4 Einstein/mol. The spectral distribution of the indigotin chemiluminescence is that of the isatin fluorescence. Addition of equimolar amounts of isatin to the reaction mixture raises the chemiluminescence quantum yield to 5.3×10^?4 Einstein/mol. A mechanism involving the intermediate formation of indigotin dioxetan is proposed.     

Laser photolysis study of the triplet states of fulvic acids in aqueous solutions

The spectral and kinetic characteristics of short-lived intermediates formed during the photolysis of aqueous and alkaline (0.1 mol l^?1 NaOH) solutions of fulvic acids (FA) were studied by the nanosecond laser photolysis technique. Laser photolysis of FA at 337 nm leads to the formation of short-lived triplet states of FA (³FA) with a quantum yield of about 1% and different relatively long-lived intermediates (with decay rate constants in deoxygenated solutions of 1.8 × 10³–2.1 × 10⁵ and 80–160 s^?1, respectively), which are characterized by absorption spectra with maximums at λ ≤ 400 nm. ³FA are quenched by atmospheric oxygen with rate constants of 5.4 × 10⁸–1.1 × 10⁹ l mol^?1 s^?1. Introduction of phenols into the solutions at concentrations up to 0.1 mol l^?1 has no appreciable effect on the decay kinetics of the detected intermediate products of FA photolysis.     

Determination of Folic Acid by Adsorptive Stripping Voltammetry at a Lead Film Electrode

An adsorptive stripping voltammetric procedure for the determination of folic acid at an in situ plated lead film electrode was described. Formation of lead film on a glassy carbon substrate and accumulation of folic acid was performed simultaneously from an acetate buffer solution of pH 5.6 at the potential ?0.88 V. The measurements were carried out from aerated solutions. The calibration graph for an accumulation time of 300 s was linear from 2×10^?9 to 5×10^?8 mol L^?1. The detection limit was 7×10^?10 mol L^?1, the relative standard deviation for 2×10^?8 mol L^?1 of folic acid was 3.9%. The proposed procedure was applied to folic acid determinations in pharmaceutical preparations.     

Chemiluminescence quantum yield in permanganate reduction reactions in acid medium

Chemiluminescence quantum yields for the reactions of permanganate with oxalic, tartaric, and citric acids; hydrazine; KBr; and FeSO₄ in aqueous solutions of sulfuric acid have been measured. The maximum quantum yield reaches 1.2 × 10^?5 einstein/mol with the chemiexcitation yield being 2%. Hence, the relatively low chemiluminescence quantum yield is due to a low yield of light emission by chemiexcited particles, rather than the low chemiexcitation yield.     

Determination of coumarins by voltammetric techniques in micellar and emulsified media

An electroanalytical study of the oxidation processes of umbelliferone and hymecromone at a glassy carbon electrode in micellar solution and emulsified medium by different voltammetric techniques is described. The non-ionic surfactant Triton X-405 in acetate-buffered medium at pH 4.8 was found to be the most suitable. Different ranges of linearity were obtained in the micellar solutions, depending on the technique used; the limits of determination for differential pulse voltammetry (DPV) at a stationary electrode were 2.9×10^?6 mol l^?1 and 3.3×10^?6 mol l^?1 for umbelliferone and hymecromone, respectively. In the emulsified medium formed with a mixture of toluene and ethyl acetate (3:2), the oxidation processes yielded similar results. With DPV, linear calibration plots were obtained in the ranges 1.0×10^?5–9.0×10^?7 mol l^?1 umbelliferone and 1.0×10^?5–2.0×10^?6 mol l^?1 hymecromone. The media used are predominantly aqueous so that special reference electrodes and solvent purification are not needed.     

Stability Improvement of Prussian Blue by a Protective Cellulose Acetate Membrane for Hydrogen Peroxide Sensing in Neutral Media

The cellulose acetate covered Prussian blue modified glassy carbon electrode (GCE/PB/CA) was fabricated as a novel hydrogen peroxide sensor. It was shown by scanning electron microscope (SEM) and atomic force microscope (AFM) that Prussian blue was covered and protected by cellulose acetate perfectly. The modified electrode showed a good electrocatalytic activity for H₂O₂ reduction in neutral aqueous solution. H₂O₂ was detected amperometrically in 0.05 mol/L phosphate buffer solutions (pH 7.0, containing 0.1 mol/L KCl as supporting electrolyte) at an applied potential of ?0.2 V (vs. SCE). The response current was proportional to the concentration of H₂O₂ in the range of 1.0×10^?5 mol/L to 2.5×10^?4 mol/L with the detection limit of 2.2×10^?6 mol/L at a signal to noise ratio 3.     

A Novel Optical Sensor for Determination of Thiocyanate

Abstract

A novel optical sensor (optode) is described for the determination of thiocyanate using methyltrioctylammonium chloride immobilized on triacetylcellulose membrane. The response to thiocyanate is the result of adsorption of [Co(SCN)₄]^2? on sensing membrane, which caused the colorless membrane to change to blue. This optode can readily be regenerated by using 0.02 mol/l sodium oxalate solution. The linear range of the method was 3.44×10^?5 to 8.61×10^?4 mol/l of thiocyanate with a limit of detection 1.51×10^?5 mol/l. The relative standard deviation for eight replicate measurements of 8.61×10^?5 and 4.30×10^?4 mol/l of thiocyanate was 3.45 and 1.23%, respectively. The sensor was successfully applied for the determination of thiocyanate in saliva of smokers, nonsmokers and various water samples.     

Investigations on Bioanalytical Chemistry Part I. On Differential Pulse Voltammetry of Bilirubin

Abstract

The electrochemical behaviour of the bilirubin in many kinds of supporting electrolytes on a glassy carbon electrode (GCE) and a hanging mercury drop electrode (HMDE) was investigated by means of anodic or cathodic differential pulse voltammetry. The influences of different methods of pre-treatment of the glassy carbon electrode was also discussed. In Na₂B₄.O₇-KH₂PO₄ buffer solution, the linear range was 2×10^?9-1×10^?9 mol/l and the detection limit was 3.3×10^?9 mol/l by anodic differential pulse voltammetry at GCE. A linear relationship holds between the peak current and the concentration of bilirubin in a concentration range of 1×10^?9-4×10^?7 mol/l with good precision and accuracy, and the limit of detection was 2×10^?10 mol/l, when cathodic differential pulse adsorption voltammetry at HMDE was used.     

Voltammetric Determination of 3‐Nitrofluoranthene and 3‐Aminofluoranthene at Boron Doped Diamond Thin‐Film Electrode

The voltammetric behavior of 3‐nitrofluoranthene and 3‐aminofluoranthene was investigated in mixed methanol‐water solutions by differential pulse voltammetry (DPV) at boron doped diamond thin‐film electrode (BDDE). Optimum conditions have been found for determination of 3‐nitrofluoranthene in the concentration range of 2×10^?8–1×10^?6 mol L^?1, and for determination 3‐aminofluorathnene in the concentration range of 2×10^?7–1×10^?5 mol L^?1, respectively. Limits of determination were 3×10^?8 mol L^?1 (3‐nitrofluoranthene) and 2×10^?7 mol L^?1 (3‐aminofluoranthene).     

Spectrofluorimetric determination of hydrogen peroxide based on the catalytic effect of peroxidase-like manganese tetrakis(sulphophenyl) porphyrin on the oxidation of homovanillic acid

Traces of hydrogen peroxide (8.5 × 10^?8–2.5 × 10^?6 mol/l) and, indirectly, glucose (3–44 × 10^?6 mol/l) can be determined by the fluorescence reaction between homovanillic acid and hydrogen peroxide. Mn-TPPS₄ is found to have very similar catalytic properties to horse peroxidase.     

Flow Injection Analysis of Tannic Acid with Inhibited Electrochemiluminescent Detection

ABSTRACT

A flow injection method has been developed for the determination of tannic acid based on its inhibition of the electrochemiluminescence of luminol. The method is simple, rapid and sensitive with a detection limit of 2×10^?8 mol/l. It is effective to determine tannic acid in the range 5×10^?8 - 1×10^?5 mol/l. The variation coefficient of eleven determinations is 1.4% for 5×10^?6 mol/l. The method has been successfully applied to the determination of tannic acid in real Chinese gall and hop pellet samples.     

Photolysis of dimethyldioxirane

Phosphorescence of methyl acetate formed by isomerization of electron-excited dimethyldioxirane is observed upon excitation at the wavelength of the absorption band of dimethyldioxirane in acetone at 77 K. The quantum yield of the photodecomposition of dimethyldioxirane at 296 K is equal to 13.1±0.7 mol Einstein⁻¹. The high quantum yield of photolysis is evidence for the chain mechanism of decomposition of dimethyldioxirane. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 938–941, May, 1997.     

PRIMARY INTERMEDIATES IN THE PULSED IRRADIATION OF RETINOIDS

Abstract Laser flash photolysis and pulse radiolysis have led to the characterisation of several shortlived intermediates formed after irradiation of retinoic acid and retinyl acetate in hexane or methanol. For retinoic acid, the triplet state, wavelength maximum 440 nm, extinction coefficient 7.3 × 10⁴ dm³ mol^?1 cm^?1, decay constant 6.2 × 10⁵ s^?1, is formed with a quantum yield of 0.012 for 347 nm excitation. The radical cation, absorption maximum 590 nm, extinction coefficient ～7 × 10⁴ dm³mol^?1 cm^?1, is formed in a biphotonic process. The radical anion, absorption maximum 510nm in hexane, 480 nm in methanol where its extinction coefficient is 1.2 × 10⁵ dm³mol^?1 cm^?1, appears to decay partially in methanol into another longer-lived neutral radical, wavelength maximum 420 nm, by loss of OH^?. For retinyl acetate, the triplet state, absorption maximum 395 nm, extinction coefficient 7.9 × 10⁴dm³mol^?1 cm^?1, decay constant 1.2 × 10⁶s^?1 is formed with a quantum yield of 0.025 for 347 nm excitation. Monophotonic photoelimination of OCOCH₃? in methanol produces the retinylic carbenium ion, wavelength maximum 590 nm, whose decay is enhanced by ammonia, k ～ 2 × 10⁶ dm³ mol^?1 s^?1 and retarded by water. The radical cation also has a wavelength maximum at 590 nm, its extinction coefficient being ～ 1.0 × 10⁵ dm³mol¹ cm^?1. The long-lived transient absorption with maximum at 385 nm, extinction coefficient 1.0 × 10⁵ dm³mol^?1 cm^?1, obtained from the reaction of the solvated electron with retinyl acetate in methanol may be due to either the radical anion itself or more likely the radical resulting from elimination of OCOCH₃? from this anion. These results suggest that skin photosensitivity caused by retinyl acetate might be greater than that due to retinoic acid.     

Investigations on Adsorption Potentiometry Part V Derivative Adsorption Chronopotentiometry of Beryllium(II)-4-[(4-diethylamino-2-hydroxypheanyl)-azo]-5-hydroxy-naphthalene-2,7-disurphonic Acid System

Abstract

An electroanalytical methood, based on derivative chronopotentiometry of the complex of beryllium(II) with 4-[(4-diethylamino-2-hydroxy-phenyl)-azo]-5-hydroxy-naphthalene-2,7-disurphonic acid (Beryllon II) accumulated adsorptively on the surface of a hanging mercury drop electrode, has been developed for determining trace beryllium in food. The dependences of the peak height on the dt/dE vs. E curve on the pre-concentration time, preconcentration potential and the constant reducing current are discussed. In 0.15 mol/1 NH_s+0.05 mol/1 NH₄Cl, 4×10^?7 mol/l Beryllon II, and at a preconcentration potential of -0.30 V (ve. SCE), the limit of detection and linear range are 1 × l0^?10 mol/l and 3 × 10^?10 -2 × l0^?7 mol/l, Iwpectively. The relative standard error of the method is 2.3% for 6 × 10^?8 mol/l Be(II). The method WBB applied to samples of food. The electrode procees hae been diecueeed.     

Development and application of the tartrazine voltammetric sensors based on molecularly imprinted polymers

A modified glassy carbon electrode was prepared as an electrochemical voltammetric sensor based on molecularly imprinted polymer film for tartrazine (TT) detection. The sensitive film was prepared by copolymerization of tartrazine and acrylamide on the carbon nanotube-modified glassy carbon electrode. The performance of the imprinted sensor was investigated by cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy in detail. Under the optimum conditions, two dynamic linear ranges of 8?×?10^?8 to 1?×?10^?6?mol?L^?1 and 1?×?10^?6 to 1?×?10^?5?mol?L^?1 were obtained, with a detection limit of 2.74?×?10^?8?mol?L^?1(S/N?=?3). This sensor was used successfully for tartrazine determination in beverages.     

Laser flash photolysis of aqueous acetaminophen solutions

The N-acetyl-4-aminophenoxyl radical, a supposed intermediate of the enzymatic oxidation of acetaminophen in living organisms, was prepared and studied by means of nanosecond laser flash photolysis. A number of important spectral-kinetic parameters of this species were determined, namely, the absorption coefficient at 440 nm ((4.2±0.2)×10³ l mol^?1cm^?1), the quantum yield of acetaminophen photoionization at 266 nm (φ= 0.03), and the rate constants for recombination (2k= (2.4±0.3))×10⁹ l mol^?1s^?1) and the reaction with the superoxide radical (k= (9±2))×10⁹ l mol^?1s^?1).     

A quantitative study of alkyl radical reactions by kinetic spectroscopy. IV. The flash photolysis of azopropanes

The flash photolysis of azo?n?propane and of azoisopropane has been studied by kinetic spectroscopy. Transient absorption spectra in theregion of 220–260 nm have been assigned to the n-propyl and isopropyl radicals. For the n-propyl radical, ?_max = 744 ± 39 l/mol cm at 245 nm and the rate constants for the mutual reactions were measured to be k_c = (1.0 ± 0.1) × 10¹⁰ l/mol sec (combination) and k_d = (1.9 ± 0.2) × 10⁹ l/mol sec (disproportionation). For the isopropyl radical, ?_max = 1280 ± 110 l/mol cm at 238 nm, with k_c = (7.7 ± 1.6) × 10⁹ l/mol sec and k_d = (5.0 ± 1.2) × 10⁹ l/mol sec The rate constant for the dissociation of the vibrationally excited triplet state of the azopropanes into radicals was measured from the variation in the quantum yield of radicals with pressure. For azo-n-propane k = (6.6 ± 1.3) × 10⁷ sec^?1, and for azoisopropane k = (1.6 ± 0.4) × 10⁸ sec^?1. Collisional deactivation of the vibrationally excited singlet and triplet states was found to occur on every collision for n-pentane; but nitrogen and argon were inefficient with a rate constant of 1.1 × 10¹⁰ l/mol sec. Spectra observed in the region of 220–260 and 370–400 nm areattributed to the cis isomers of the parent trans-azopropanes. These are formed, as permanent products, in increasing amounts as the pressure is increased.     

Kinetics and mechanism of photochemical reactions of peroxomonosulfate in the presence and absence of 2-propanol

The photochemical decomposition of peroxomonosulfate (PMS) in the presence and absence of 2-propanol at 25°C was found to obey an overall first-order rate – d[PMS]/dt = k_?[PMS]. In the absence of 2-propanol, the quantum yield ≤ for the decomposition of PMS was found to depend upon the concentration of PMS at [PMS] > 2 × 10^?M, and is independent of concentration at [PMS] > 2 × 10^?2M. The quantum yield in the presence of 2-propanol was found to be 3.03 at [PMS] = 1 × 10^?2M and 4.45 at higher concentrations of PMS. In the pH range of 2–9.0 the quantum yield was found to be independent of pH, and the overall rate constant k_? was found to be 6.49 × 10^?3 s^?1 and 1.68 × 10^?3 s^?1, respectively, in the presence and absence of isopropanol. A suitable chain mechanism is proposed and explained.     

Determination of the Natural Dissolved Concentration of Zirconium in Seawater by Adsorptive Stripping Voltammetry

A voltammetric method was developed for zirconium determination as Zr(IV)‐cupferron‐oxalate‐diphenylguanidine complex based on adsorptive accumulation at the HMDE (E_peak=?0.95 V). The supporting electrolyte was a mixture of acetate/acetic acid (pH 4.6) and ammonium acetate (pH 5.7) solutions. E_ads=?0.6 V (vs. Ag/AgCl), t_ads=400 s, 10 mV s^?1 scan rate, and DP mode were the main parameters. The linear range was 0.033 to 3.3×10^?9 mol L^?1, and the LOD and LOQ (t_ads=400 s) were 0.77 and 1.6×10^?11 mol L^?1, respectively. The method was adequate for seawater samples, although not sufficiently sensitive for surface waters.     

Pyrene fluorescence quenching by aromatic azides

Pyrene fluorescence quenching by phenylazide derivatives with donor and acceptor substituents has been studied by fluorescence spectroscopy and flash photolysis. The rate constants of quenching (k _q) in acetonitrile ((0.2–1.2) × 10¹⁰ l mol^?1 s^?1) are found to be close to a diffusion limit; the rate constants were somewhat higher for perfluoro-substituted arylazides. It is found that k _q does not depend on solvent polarity; the formation of the pyrene cation in the course of pyrene fluorescence quenching by tolylazide was not detected. Pyrene fluorescence quenching occurred by an energy-transfer mechanism; this is supported by the coincidence of the quantum yields of the direct and sensitized photodecomposition of tolylazide. As estimated, energy transfer in rigid media occurs at characteristic distances of about 10 Å.