Laser-excited molecular flourescence spectrometry for the determination of traces of nonmetals : Part 1. determination of traces of fluoride,chloride and bromide based on diatomic molecules in a graphite furnace

For the determination of flouride, chloride and bromide, a suitable metal ion is added in a modified graphite tube atomizer. After drying and ashing, the substances are vaporized and diatomic molecules between the metal and nonmetal are formed. These molecules are excited by a pulsed dye laser and the resulting fluorescence is measured. At constant metal concentration, the fluorescence is proportional to the halide concentration. The diatomic molecules used are MgF, InCl and AlBr. The detection limits are 11 pg of fluoride, 15 pg of chloride and 70 pg of bromide in the 10-μl injections, corresponding to 6 x 10^?8 mol l^?1 fluoride, 4 x 10^?8 mol l^?1 chloride and 9 x 10^?8 mol l^?1 bromides.     

Electrochemical Studies and Square‐Wave Adsorptive Stripping Voltammetry of Spironolactone Drug

Abstract

A sensitive and reliable stripping voltammetric method was developed to determine Spironolactone drug. This method is based on the adsorptive accumulation of the drug at a hanging mercury drop electrode and then a negative sweep was initiated, which yield a well defined cathodic peak at ?1000 mV versus Ag/AgCl reference electrode. To achieve high sensitivity, various experimental and instrumental variables were investigated such as supporting electrolyte, pH, accumulation time and potential, drug concentration, scan rate, frequency, pulse amplitude, convection rate and working electrode area. The monitored adsorptive current was directly proportional to the concentration of Spironolactone and it shows a linear response in the range from 1×10^?8 to 2.5×10^?7 mol l^?1 (correlation coefficient=0.999) and the detection limit (S/N=3) is 1.72×10^?10 mol l^?1 at an accumulation time of 90 sec. The developed AdSV procedure shows a good reproducibility, the relative standard deviation RSD% (n=8) at a concentration level of 1.5×10^?7 mol l^?1 was 1.4%, whereas the method accuracy was indicated via the mean recovery of 97.5%±2.04. Possible interferences by several substances usually present in the pharmaceutical formulations have been also evaluated. The applicability of this approach was illustrated by the determination of Spironolactone in pharmaceutical preparation and biological fluids such as serum and urine.     

Spectrophotometric Determination of Hydrogen Peroxide and Glucose Based on Hemin Peroxidase-Like Catalyzed Oxidation of Bromopyrogallol Red

In an ammonium buffer medium at pH 8.9–9.5, hemin exhibits mimetic peroxidase activity, and has a catalytic effect on the oxidative decoloration of bromopyrogallol red (BPR) with hydrogen peroxide. On this basis and in presence of ethanol as an effect-enhancing agent, a spectrophotometric determination of hydrogen peroxide is described with an apparent molar absorptivity of 4.00×10⁴?l?mol^?1?cm^?1 and a linear range from 3.2×10^?7 to 3.2×10^?5?mol?l^?1. BPR has advantages over some of widely used chromogenic substrates in aspects of sensitivity, simplicity and detection wavelength, while hemin has better stability than peroxidase. The system can be easily coupled with a glucose oxidase-catalyzed reaction, and glucose in the concentration range of 6.0×10^?7? 3.2×10^?5?mol?l^?1 is spectrophotometrically determined. The method has been applied to the analyses of synthetic water and human serum samples. The Michaelis parameters and the mechanism of the mimetic peroxidase reaction are also investigated.     

Effects of iron on the degradation of triphenyltin by pyoverdins isolated from Pseudomonas chlororaphis

The yellow compound pyoverdin was isolated from the bacteria Pseudomonas chlororaphis, isolated from mud in Japan. A study of the effects of iron, phosphorus, manganese and zinc on degradation of triphenyltin (TPT) by pyoverdin (20 mg) was carried out in distilled water (30 ml) containing 6 µg l^?1 concentration of TPT at 20 °C for 48 or 96 h. The organotins in water were analyzed by gas chromatograph–mass spectrometry in the selected ion mode. The degradation of TPT by pyoverdin decreased with increase of phosphorus at 0–35 mg l^?1 and Fe‐EDTA at 0–2 mg l^?1 concentrations. Also, degradation of diphenyltin by pyoverdin decreased with increase of Mn‐EDTA at 0–1 mg l^?1 and Zn‐EDTA at 0–1 mg l^?1. On the other hand, degradation of TPT by pyoverdin was found to be unaffected by manganese and zinc in water. Copyright © 2002 John Wiley & Sons, Ltd.     

Adsorption voltammetry of the vanadium-2-(5′-bromo-2′-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) system

The behaviour of the vanadium(V) complex with 5-Br-PADAP at a mercury electrode was investigated in HOAcNaOAc. The adsorption phenomena were observed by linear-sweep voltammetry. The mechanism of the electrode reaction was found to be the irreversible reduction of the V(V) in the complex adsorbed on the surface of the electrode to the V(IV) complex with 5-Br-PADAP. In 0.02 mol l^?1 HOAc-0.012 mol l^?1 NaOAc (pH 4.5) and 1 × 10^?6 mol l^?1 5-Br-PADAP, the detection limits of linear-sweep adsorption voltammetry and 1.5th-order derivative adsorption voltammetry are 5 × 10^?10 and 2.5 × 10^?11 mol l^?1 , respectively. The method was applied to samples of ore (Geological Deposit).     

Polarographic determination of pirimicarb

A sensitive and selective polarographic method for the determination of pirimicarb is proposed. Linear calibration graphs were obtained by differential-pulse polarography in the 3.0 × 10^?7–9.0 × 10^?5 mol l^?1 range, the limit of determination being 2.8 × 10^?7 mol l^?1. No interferences were observed from other carbamate pesticides such as aminocarb, bendiocarb or carbaryl and only a matrix effect occurs in the presence of methiocarb. The method was applied to the determination of Pirimicarb in water samples with good recoveries.     

Ion-aggregation and thermal expansion in styrene-based ionomers

The linear thermal-expansion coefficients (α) of styrene–sodium methacrylate copolymers were studied as a function of the concentration of sodium methacrylate comonomer. Over the concentration range studied (0.61–9.0 mole % sodium methacrylate), the expansion coefficients of the glass α_g and of the liquid α_l were independent of ion concentration. Average values for these quantities were α_g = (6.9 ± 0.9) × 10^?5 deg^?1 and α_l = (16.0 ± 2.0) × 10^?5 deg^?1. When samples of concentrations above 6 mole % were heated from room temperature, a low value for the liquid-expansion coefficient α_l was observed in the first runs. This quantity had an average value of (12.0 ± 1.9) × 10^?5 deg^?1. Heating of the 6.5 mole % sample from room temperature followed by cycling from the glass transition temperature T_g to successively higher temperatures resulted in a gradual increase in liquid-expansion coefficient. The results are consistent with the hypothesis of the existence of various types of ionic aggregates in these polymers, with the state of aggregation changing at approximately (5–6) % of ions. Experimental T_g values, which increase with ion concentration over the entire range, are consistent with the results of previous studies.     

Preconcentration of palladium(II) from water with thionalide loaded on silica gel

2-Mercapto-N-2-naphthylacetamide (thionalide) on silica gel is used for rapid preconcentration of μg l^?1 levels of palladium(II) from aqueous solution, followed by atomic absorption spectrometric measurement. In batch experiments, palladium was quantitatively retained on the gel from solutions 5 M in acid to pH 8; equilibrium was achieved within 10 s. The chelating capacity of the gel was 7.5 μmol Pd g^?1 at pH < 4. The effect of flow rate on retention was studied. Palladium retained on the column was completely eluted with 20 ml of 0.2 M thiourea in 0.1 M hydrochloric acid. The palladium concentration in sea water is shown to be < 0.3 μg l^?1.     

Electrochemical Reduction Behavior and Polarographic Determination of Methoxy Triazine Herbicides in Environmental Samples

The electrochemical reduction behavior of 1,3,5-triazine herbicides, Atraton (AN), Prometon (PN), Secbumeton (SN), and Terbumeton (TN) at mercury electrodes was studied in aqueous Britton Robinson buffer (BR) solutions by using different voltammetric techniques. The nature of the electrode process was examined. Number of electrons involved in the reduction process of all the four compounds was evaluated and a reduction mechanism was proposed. The electrolysis products were separated and identified by IR spectra. For analytical purposes, BR buffer of pH 4.0 was chosen as working medium for all the four analytes. The detection limits were found to be 1.5 × 10^?8 mol l^?1, 2 × 10^?8 mol l^?1, 2.8 × 10^?8 mol l^?1, and 1 × 10^?8 mol l^?1 for AN, PN, SN, and TN, respectively. A differential pulse voltammetric method was developed for the determination of these compounds in agricultural formulations, water, and soil samples. The interference from the ions and other herbicides were also evaluated.     

A predictive-kinetic method for the quantitation of amino acids with ninhydrin

The development and evaluation of a predictive-kinetic method for quantifying amino acids based on reactions with ninhydrin are described. Conditions are developed for which reactions are pseudo-first-order in the amino acid. Absorbance vs. time data from the kinetic region of the reaction (1–3 half-lives) are fitted to a first-order model to predict the total absorbance change that would occur if the reaction were monitored to completion. Computed absorbance changes vary linearly with amino acid concentration between 1 × 10^?5 and 5 × 10^?5 mol l^?1. Results are virtually independent of changes in temperature (± 1° C) and ninhydrin concentration (± 3 × 10^?3 mol l^?1).     

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.     

Determination of humic acid by chemiluminescence

The analytical utility of the chemiluminescence resulting from the reaction of humic acid with permanganate is investigated. The chemiluminescence response curve rises sharply to a peak value at about 0.5 s after mixing and decays somewhat more slowly. The peak signal for a fixed humic acid concentration is shown to pass through a maximum near a permanganate concentration of 17 μmol l^-1 and to increase continuously with potassium hydroxide concentration up to 2.0 mol l^-1. Calibration plots of peak signal vs. humic acid concentration exhibit complex behaviour, being approximately linear up to about 20 mg l^-1, curving slightly toward the concentration axis up to about 40 mg l^-1, and then curving away from the concentration axis above 40 mg l^-1. The detection limit for humic acid is about 0.7 mg l^-1. No interference is observed for thirteen common inorganic species at typical levels in water samples. Substantial differences are observed for humic acid in selected samples determined by the chemiluminescence and visible absorption procedures.     

Intermolecular interaction between squarylium cyanine and porphyrin

In this paper, the interaction between squarylium cyanine and porphyrin in chloroform is investigated by absorption and fluorescence spectroscopy. Emphasis has been put on the mechanism of intermolecular energy transfer. The overlap integral J between the absorption spectrum of squarylium cyanine and the fluorescence spectrum of porphyrin was calculated, which reveals that the singlet-singlet energy transfer may occur from porphyrin to squarylium cyanine in solution. In comparison of the observed rate constant [kqII=6.1 ×1013 (mol/L)-1·s-1] for fluorescence quenching of porphyrin by squarylium cyanine with the diffusion rate constant in chloroform [kdif=1.1×1010 (mol/L)-1·s-1] and the rate of energy transfer [ket≤6.7×104 (mol/L)-1·s-1 in the experimentally dilute solutions] estimated from Forster formula, the possibility of energy transfer by electron exchange or/and coulombic mechanism could be excluded. So it has been definitely convinced that the intermolecuiar energy transfer between them is     

Electrochemical determination of norepinephrine on the membrane of silver nanoparticles doped poly-glycine eliminating the interference of ascorbic acid

The silver nanoparticles doped poly-glycine composite membrane was prepared by cyclic voltammetry on the surface of the glassy carbon electrode (GCE). The morphology and electrochemical properties were characterized by scanning electron microscopy and cyclic voltammetry, respectively, and in detail, the electrochemical behaviors of the norepinephrine (NE) on this membrane were studied. The results showed that the membrane had good catalytic properties for the oxidative–reductive reaction of NE. NE had a couple of sensitive oxidative-reductive current peaks. The reductive peak currents were linearly with its concentration in the range of 1.90?×?10^?7 to 7.00?×?10^?6 and 7.00?×?10^?6 to 1.00?×?10^?4?mol l^?1, and the linear regressive equations were i _pc (A)?=?3.73?×?10^?6?+?0.70C (mol l^?1), i _pc (A)?=?9.83?×?10^?5?+?0.12C (mol l^?1), respectively, with the relate coefficient (r) of 0.9926 and 0.9944. The detection limit was 1.2?×?10^?7?mol l^?1 (S/N?=?3), which could be used to determine the content of NE and at the same time, eliminate the interference of the ascorbic acid (AA). The proposed method had high sensitivity, good selectivity and stability.     

High-accuracy differential-pulse anodic stripping voltammetry with indium as an internal standard

Indium(III) is used as an internal standard for the determination of cadmium, copper and lead at the 20 ng g^?1 level by using differential-pulse anodic stripping voltammetry; the supporting electrolyte is 1.0 mol l^?1 ammonium bromide/0.25 mol l^?1 nitric acid. For each solution, each stripping peak of interest is normalized to the corresponding peak height obtained in the same voltammogram for a known, added concentration of indium(III). A calibration curve is prepared for each element by using these normalized peak heights. The technique is demonstrated for NBS SRM 1643b (Trace Elements in Water). The relative standard deviations for six independent determinations of Cd, Cu, and Pb at the 20 ng g^?1 level are 1.9%, 5.4%, and 1.2%, respectively. The imprecision for copper is limited by the sloping baseline at its stripping potential. The detection limit for each element is less than 1 ng g^?1.     

The Nonreversibility of Adsorption-Desorption of Dieldrin and Lindane on Chitin in Seawater

Abstract

Adsorption and desorption of dieldrin and lindane on chitin were investigated in seawater batch tests as a function of chitin concentration, temperature, pH and salinity. For chitin concentrations ranging from 0.5 g l^?1 to 12.5 g l^?1, the pesticide concentrations were varied from 4 μgl^?1 to 65 μg^?1 for dieldrin and from 40 μl^?1 to 680 μg l^?1 for lindane. Both dieldrin and lindane show adsorption-desorption hysteresis at low chitin concentration. At high chitin concentrations (m > 6.25 g l^?1 for dieldrin and m > 10 gl^?1 for lindane) both pesticides exhibit reversible behaviour. However, only lindane adsorption is affected by chitin concentration. These types of behaviour remain fixed in prewashed chitin. However, an increase in the temperature and a decrease in the salinity made the process become reversible. A resistant-reversible two component model has been applied to account for these types of behaviour and provides a way to explain most of the observed effects by defining mass independent distribution coefficients.     

Parameters Affecting the Peroxyoxalate Chemiluminescence

ABSTRACT

A careful study of the parameters affecting the chemiluminescent reaction of TCPO (bis(2,4,6-trichlorophenyl)oxalate) and 2-NPO (bis(2-nitrophenyl)oxalate) with hydrogen peroxide, in the presence of imidazole (used as buffer and catalyst) and the fluorophore 3-AFA (3-aminofluoranthene), was carried out in acetonitrile/water medium. The data are reported in terms of the time (t_Imax) required for the relative maximum chemiluminescence intensity (I_max) and the area (A) under the curve of intensity νs. time. At controlled acidity and high unprotonated imidazole concentration ([IMI] = 1x10^?2 mol.L^?1), the I_max and t_Imax values do not depend on the acetonitrile/water ratio. The CL intensity is maximum at around pH 6.0 (higher buffer capacity). For 1x10^?2 < [IMI] < 1x10^?4 mol.L^?1, the area is largest when [IMI] = 1x10^?3 mol.L^?1 and linearly dependent on the hydrogen peroxide concentration (10^?5 ? 10^?3 mol.L^?1). The area is also enhanced by increasing the fluorophore concentration. The acidity controls the unprotonated imidazole and H⁺ concentration. Several errors can arise from quantitative analyses carried out without control of the HIMI⁺ and IMI concentrations.     

Binding of Copper(II) to Pectins by Electrochemical Methods

The interaction between Cu(II) and pectin extracted from citrus fruit was studied in KNO₃ 0.10 mol dm^?3 at 25 °C and pH 5.5, using ion selective electrode potentiometry and voltammetry, namely differential pulse polarography and square‐wave voltammetry. Although many independent variables may affect Cu(II)‐polymer interactions such as charge density, polymer concentration and copper to polymer concentration ratio, a good fitting was observed for the model with ML and ML₂ complex species, when M:L total concentration (mol dm^?3) ratio varies from 0.2 to 2.7 and the ligand concentration is in the range (0.2 to 1) g dm^?3, i.e., (0.4 to 2)×10^?3 mol COO^? dm^?3. The complex parameters found in these conditions were log β_CuL=3.5±0.1 and log β_CuL2= 8.0±0.2. For lower total ligand and total metal ion concentrations, used in voltammetry, the interaction Cu(II)‐pectin is affected by a cooperative mode (increase of metal ion‐ligand affinity) when the total metal ion concentration increases and by an anti‐cooperative mode when the total ligand concentration increases, possibly due to different conformations of the polymer.     

INTERCONVERSION OF BACTERIOCHLOROPHYLL c AGGREGATES IN SOLID FILMS UPON ORGANIC VAPOR TREATMENT

Bacteriochlorophyll c (BChl c) solid films were prepared from a carbon tetrachloride solution on CaF₂ plates as artificial aggregates. Effects of organic vapor such as acetone and tetrahydrofuran (THF) on the BChl c films were studied by absorption and Fourier-transform infrared spectroscopy. Two major homologs (R[E,E]BChl c_F and R[P,E]BChl c_F) and one minor homolog (S[I,E]BChl c) isolated from the green photosynthetic bacterium Chlorobium limicola strain 6230 were examined for the experiments. The BChl c polymeric aggregates absorbing at739–753 nm similar to those in the chlorosome were induced for all homologs upon the treatment of BChl c solid film with acetone vapor. The 13¹-keto C=O stretching band in the R[E,E]BChl c_F solid film showed a downward shift from 1651 cm^?1to 1643 cm^?1 with a concomitant shift of the 3¹-OH stretching bands from 3337 and 3238 cm^?1 to 3163 cm^?1. It was suggested that the lower aggregates brought about by Mg…O=C(13¹) and (3¹)O…O=C(13¹) bonds were transformed into the higher aggregates strongly hydrogen-bonded in a Mg…(3¹)O-H…O=C(13^l) interaction. They were transformed to a monomer-like form absorbing at 667 nm upon exposure to THF vapor and were reversibly converted to the higher aggregates upon removal of THF molecules in vacuo.     

On the mechanism of the Co2(CO)8 catalyzed hydroformylation of olefins in hydrocarbon solvents. A high pressure UV and IR study

High pressure IR and UV spectroscopic experiments confirm the Heck and Breslow mechanism of the hydroformylation of 1-octene and cyclohexene with Co₂(CO)₈ as the starting catalyst. The major repeating unit is HCo(CO)₄, which is formed via the reaction of acylcobalt tetracarbonyl with H₂. The rates are 6.7 × 10^?4 mol l^?1 min^?1 and 8.8 × 10^?5 mol l^?1 min^?1 for 1-octene and cyclohexene, respectively at 80°C and 95 bar CO/H₂ = 1 in methylcyclohexane. The alternative reaction of RCOCo(CO)₄ with HCo(CO)₄ is only a minor pathway, with rates of 1.8 × 10^?5 mol l^?1 min^?1 and 1.1 × 10^?5 mol l^?1 min^?1 for 1-octene and cyclohexene, respectively. It represents an exit from the catalytic cycle. The activation of the catalyst precursor Co₂(CO)₈ is the slowest step of the reaction.