Removal of humic acid and surfactant interferences in trace metal determinations by differential-pulse anodic stripping voltammetry with use of adsorption and chelate ion-exchanger columns in a flow-injection system

A flow-injection differential-pulse anodic stripping voltammetry (d.p.a.s.v.) method is modified so that interferences from humic acids or surfactants are eliminated. The injected, slightly acidic sample is passed through a silica anion-exchanger column to remove compoundswith a strong tendency to adsorb to the electrode. The sample then passes to a chelate ion-exchange column containing immobilized 8-quinolinol. The metal ions are retained and later eluted with acid into the voltammetric cell. The results show that the interferences from up to 500 mg 1^–1 humic acid or at least 50 mg 1^-1 Triton X-100 can be removed and that the metal ion can be determined in a range similar to that for normal d.p.a.s.v. methods. The complete cycle time for a determination was 12 min.     

A direct differential pulse anodic stripping voltammetric method for the determination of thallium in natural waters

A dual direct method for the ultratrace determination of thallium in natural waters by differential pulse anodic stripping voltamrnetry (d.p.a.s.v.) is presented. D.p.a.s.v. at the hanging mercury drop electrode and at the mercury film electrode is used in the concentration ranges 0.5–100 μg Tl l^-1, and 0.01–10 μg Tl l^-1, respectively. Quantification is aided by the technique of standard additions. The response of the method is optimized for typical natural surface water matrices. An intercomparison of thalium determinations performed by the two anodic stripping methods and electrothermal-atomization atomic absorption spectrometry on normal and thallium-spiked surface water samples demonstrates equivalent accuracy within the range where atomic absorption is applicable. The method appears free from serious interferences.     

Performance of theoretical methods and basis sets on the molecular structure, atomisation and ionisation energies, electron affinity, and vibrational spectrum of silylene

This work compares the performance of theoretical methods and basis sets on the molecular structure, atomisation and ionisation energies, electron affinity, and vibrational spectrum of silylene. Silylene, its cation and anion have been studied in ¹ A ₁, ² A ₁ and ² B ₁ states, respectively, in the gas phase and C_2v symmetry. The methods considered are second-order Møller-Plesset perturbation theory (MP2), the density functional theory (DFT), Gaussian-2 (G2) and complete basis set methods (CBS-4M and CBS-Q). The basis sets used are 6-31G(d,p), 6-311G(d,p), 6-31++G(d,p) and 6-311++G(d,p). The functional used for the DFT method is B3LYP. Silylene and its cation and anion have been optimised using the MP2 and DFT methods and the named basis sets. Single-point energy calculations (G2, CBS-4M and CBS-Q) were performed using MP2/6-311++G(d,p) structures and these energies have been used to calculate atomisation energy, ionisation energy and adiabatic electron affinity. Frequency calculations were also done and the raw vibrational frequencies were assigned. It is interesting to note the close similarity between the predicted parameters and some of the available literature values. The results obtained are consistent and converge with different basis sets with improved size and quality. However, the parameters obtained are very much method dependent.     

The determination of phenol and kinetic studies on the monobromination of phenol by a pulse coulometric technique

A method for the coulometric determination of phenol is described in which constant current pulses are used to electrogenerate bromine and a current recorder is used to follow the bromination reaction of phenol. Solutions containing 10^-4 to 7.10^-6M phenol are determined with a precision of 1 %. A general method for determining the kinetics of bromination reactions is postulated and used for the determination of the rate constant of the monobromination of phenol. The rate constant for the reaction in which the reacting species are the neutral phenol molecule and the bromine molecule, was found to be 1.6.10⁵1/mole sec.     

Polarography of disodium pentacyanonitrosylferrate(II): Part 2. Determination at Therapeutic Levels in Serum,Plasma, and Whole Blood

Disodium pentacyanonitrosylferrat(II) (sodium nitroprusside) is determined at therapeutic (ng ml^?1) levels in plasma, serum and blood with conventional and high-performance differential pulse polarography (d.p.p. and h.p.d.p.p.) at a dropping mercury electrode or a static mercury drop electrode. Serum or plasma (3 ml) is treated with perchloric acid containing 1 mg ml^?1 potassium hexacyanoferrate(II), centrifuged for 10 min and subjected to polarography. For spiked serum, calibration graphs are linear over the range 30–1000 ng ml^?1 sodium nitroprusside, regardless of the polarographic technique; the estimated detection limit is 15 ng ml^?1 (5 × 10^?8 M). Calculated therapeutic levels range from 100 to 1000 ng ml^?1. Similar results were obtained for spiked plasma. A similar procedure is suitable for whole blood and was used to study the in-vitro degradation of sodium nitroprusside (200 ng ml^?1) on incubation at 37°C. The in-vitro loss is rapid (t_{$\text{1}\text{2}$} ≈ 6 min) but meaningful in-vivo levels can be obtained when the blood is collected in a 0.9% sodium chloride solution at 0°C. Thiocyanate, the main metabolite of nitroprusside, and thiosulphate, which is a potential antidote for cyanide, do not interfere.     

The simultaneous determination of osmium,ruthenium, iridium and gold in platinum by neutron activation analysis

Osmium, ruthenium, iridiuim and gold can be determined simultaneously in 100-mg platinum samples after irradiation for 11 days at a thermal neutron flux of 4'1011 n.cm^-2.sec^-1. An addition method of analysis is used; samples are dissolved in small sealed silica tubes before activation. After irradiation, Os and Ru are distilled from sulfuric acid-sodium bromate, Ru being determined by counting the 498-keV peak of ¹⁰³Ru; Os is determined after a second distillation. Gold is extracted with ethyl acetate from the residue of the first distillation; the ratio ¹⁹⁸Au/¹⁹⁹Au is a direct measure for the gold content, with appropriate correction for the second-order reaction ¹⁹⁶Pt(n,γ)¹⁹⁷Pt→¹⁹⁷Au(n,γ)¹⁹⁸Au. Ir is determined in the residual aqueous phase using the 317-keV peak of ¹⁹²Ir; a correction for the platinum activity (¹⁹¹Pt) is made. The lower limit of determination is ca. 0.5 p.p.m. for ruthenium, ca. 0.2 p.p.m. for osmium, ca. O.1 p.p.m. for gold and ca. O.1 p.p.m. for iridium. After a separation of Pt from Ir, the sensitivity for Ir can easily be improved to < 10 p.p.b.     

Synthesis of new cyano-substituted analogues of Tröger's bases from bromo-derivatives. A stereochemical dependence of long-range (nJHH,n = 4, 5, and 6) proton–proton and proton–carbon (nJCH,n = 1, 2, 3, 4, and 5) coupling constants of these compounds

A free-catalyst microwave-assisted cyanation of brominated Tröger's base derivatives ( 2a - f ) is reported. The procedure is simple, efficient, and clean affording the nitrile compounds ( 3a - e, I ) in very good yields. Complete assignment of ¹H and ¹³C chemical shifts of 2a - f, I and 3a - d, I was achieved using gradient selected 1D nuclear magnetic resonance (NMR) techniques (1D zTOCSY, PSYCHE, DPFGSE NOE, and DEPT), homonuclear 2D NMR techniques (gCOSY and zTOCSY), and heteronuclear 2D NMR techniques (gHSQCAD/or pure-shift gHSQCAD, gHMBCAD, bsHSQCNOESY, and gHSQCAD-TOCSY) with adiabatic pulses. Determination of the long-range proton–proton coupling constants ⁿJ_HH (n = 4, 5, 6) was accomplished by simultaneous irradiation of two protons at appropriate power levels. In turn, determined coupling constants were tested by an iterative simulation program by calculating the ¹H NMR spectrum and comparing it to the experimental spectrum. The excitation-sculptured indirect-detection experiment (EXSIDE) and ¹H-¹⁵N CIGARAD-HMBC (constant time inverse-detection gradient accordion rescaled heteronuclear multiple bond correlation) were applied for determination of long-range carbon–proton coupling constants ⁿJ_CH (n = 2, 3, and 4) and for assignment of ¹⁵N chemical shift at natural abundance, respectively. DFT/B3LYP optimization studies were performed in order to determine the geometry of 2c using 6-31G(d,p), 6-311G(d,p), and 6–311 + G(d,p) basis sets. For calculation of ¹H and ¹³C chemical shifts, ⁿJ_HH (n = 2, 3, 4, 5, and 6), and ⁿJ_CH (n = 1, 2, 3, and 4) coupling constants, the GIAO method was employed at the B3LYP/6-31G(d,p), B3LYP/6-31+G(d,p), B3LYP/6-311+G(d,p), B3LYP/6-311++G(2d,2p), B3LYP/cc-pVTZ), and B3LYP/aug-cc-pVTZ) levels of theory. For the first time, a stereochemical dependence magnitude of the long-range ⁿJ_HH (n = 4, 5, and 6) and ⁿJ_CH (n = 1, 2, 3, 4, and 5) have been found in bromo-substituted analogues of Tröger's bases.     

The reliable determination of mercury traces in sea water by subtractive differential pulse voltammetry at the twin gold electrode

In the marine environment, mercury has the greatest toxicological significance among the common metals. By combining several basic principles of advanced voltammetry, a reliable and accurate procedure with a determination limit of 1 ng l^-1 has been developed. The complete method, which is necessary for application to sea water, consists of cathodic deposition under programmed polarization with intermittent short anodic pulses to strip the co-deposited copper usually present in sea water in substantially larger amounts than mercury, subsequent medium exchange to 0.1 M HClO₄–2.5 × 10^-3 M HCl, and differential pulse anodic stripping in the subtractive mode at a twin gold disc electrode system. Construction of the twin electrode (which has its two halves insulated from each other), characteristics of the stages of the voltammetric procedure and its performance are presented. The method is very flexible and can be adapted and simplified for application to other aqueous matrices and natural waters with mercury levels above 100 ng l^-1. The data from a case study yielding a survey of the mercury content in the German North Sea coastal waters demonstrate the significance of this new analytical procedure for research and monitoring tasks in marine trace chemistry.     

Synthesis, spectroscopic and DFT investigation of dimethyl-2-(5-acetyl-2,2-dimethyl-4,6-dioxo-1,3-dioxan-5-yl)-3-(triphenylphosphinylidene)succinate

Dimethyl-2-(5-acetyl-2,2-dimethyl-4,6-dioxo-1,3-dioxan-5-yl)-3-(triphenylphosphinylidene)succinate has been synthesized and characterized by elemental analysis, FT-IR and ¹H, ¹³C and ³¹P NMR. The vibrational wavenumbers, gauge including atomic orbital (GIAO) ¹H and ¹³C chemical shift values of title compound in the ground state have been computed with density functional theory method (DFT) and the B3LYP functional. The basis sets used are 6-311G(d,p) and 6-31G(d). The harmonic vibrational wavenumbers have been computed and the scaled values have been compared with the experimental FT-IR spectra. The complete assignments have been performed on basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. Most of the computed wavenumbers are found to be in good agreement with the observed spectrum.     

Analytical Determination of N-(2-Mercapto Propionyl)Glycine (Tiopronin) by Voltammetric Methods

Abstract

The anodic processes which occur at the mercury electrode in N-(2-mercaptopropinyl)glycine (tiopronin) solutions are studied by polarographic techniques (d.c., d.p. and a.c₁.), controlled potential coulometry and cathodic stripping voltammetry. According to the observed electrochemical behaviour the overall electrode process is the formation of a mercury(II)-mercaptide. Adsorption on the electrode of both the mercaptide and the free thiol is present. The d.p.p. peak at -0.58 V or the voltammetric stripping peak at -0.56 V are used for the analytical determination of N-(2-mercaptopropionyl)glycine within the concentration ranges 7.0 10^?5 - 6.8 10^?6 mol 1^?1 or 3.0 10^?7 - 1.0 10^?9 mol I^?1, respectively. Calibration functions are reported in both cases. The interference of several organic compounds is described.     

Theoretical Gas Phase Study of the Gauche and Trans Conformers of 1-Bromo-2-Iodoethane and Solvent Effects

This is a gas-phase study of the gauche and trans conformers of 1-bromo-2-iodoethane. The methods used are the second-order Møller-Plesset theory (MP2) and density functional theory (DFT). The functional used for the DFT method is B3LYP and the basis sets used are 6-311++G(d,p) for all atoms except that different basis sets, namely 3-21G, LANECP, CRENBL ECP, Stuttgart RLC ECP and 6-311G(d,p), have been explored for the iodine atom. The results indicate that the trans conformer is preferred. The energy difference between the gauche and trans conformers (ΔE _g?t) and related thermodynamic parameters are reported. The ΔE _g?t values are 12.50 kJ?mol^?1 (B3LYP) and 10.00 kJ?mol^?1 (MP2) with the basis sets being 6-311++G(d,p)[C,H,Br]/6-311G(d,p)[I]. The conformers of 1-bromo-2-iodoethane have also been subjected to vibrational analysis. The results from the two theoretical levels are in good agreement but they are not much affected by the basis set of the iodine atom. The study has been extended to explore solvent effects using Self-Consistent Reaction Field methods. The structural parameters of the conformers are little affected by the polarity of the solvent but ΔE _g?t decreases and the solvation Gibbs energy increases with increasing polarity of the solvent.     

A Selective Fluoroionophore Based on BODIPY‐functionalized Magnetic Silica Nanoparticles: Removal of Pb2+ from Human Blood

Get the lead out : The title fluorescence receptor exhibits a high affinity and selectivity for Pb²⁺ over competing metal ions in water (see picture) with an overall emission change of approximately 8‐fold at the emission maximum for Pb²⁺. The fluorescence receptor can remove 96 % of 100 ppb Pb²⁺ from human blood, and can be useful and effective for the selective and rapid removal of Pb²⁺ in vivo.

     

Determination of mercury in bismuth by neutron activation analysis

A method has been developed for the determination of traces of mercury in bismuth by neutron activation analysis. After sample irradiation at a flux of 7 · 10¹³ n cm^-2 s^-1 for 20 min, mercury was separated from bismuth by addition of ammonium sulfide and re-dissolution of bismuth (matrix) sulfide with nitric acid, and filtration of sulfur containing mercury on a membrane filter. The activity of the 68- or 68–77-keV region, counted with a Ge(Li) or NaI(Tl) detector, was used for quantitative measurements. The method was applied to bismuth samples containing 0.1–100 p.p.m. of mercury.     

FT-IR, FT-Raman vibrational spectra and molecular structure investigation of 2-chloro-4-methylaniline: A combined experimental and theoretical study

In this work, the experimental and theoretical vibrational spectra of 2-chloro-4-methylaniline (2Cl4MA, C₇H₈NCl) were studied. FT-IR and FT-Raman spectra of 2Cl4MA in the liquid phase have been recorded in the region 4000–400 cm⁻¹ and 3500–50 cm⁻¹, respectively. The structural and spectroscopic data of the molecule in the ground state have been calculated by using Hartree-Fock (HF) and density functional method (B3LYP) with the 6-31G(d), 6-31G(d,p), 6-31+G(d,p), 6-31++G(d,p) and 6-311G(d), 6-311G(d,p), 6-311+G(d,p), 6-311++G(d,p) basis sets. The vibrational frequencies have been calculated and scaled values have been compared with experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The DFT-B3LYP/6-311++G(d,p) calculations have been found more reliable than the ab initio HF/6-311++G(d,p) calculations for the vibrational study of 2Cl4MA. The optimized geometric parameters (bond lengths and bond angles) were compared with experimental values of aniline and p-methylaniline molecules.     

Contribution à l'électrochimie des thiols et disulfures : Partie IV. Polarographies d.c., a.c. et impulsionnelle différentielle de la cystéamine et de la cystamine

The electrochemical behaviour of the cysteamine—cystamine system was investigated by the d.c.a.c. and d.p.p. techniques, as functions of concentration and pH. Adsorption phenomens were observed, and the cystéamine anodic and the cystamine cathodic waves were found to be diffusion-controlled. Separation of these two sulfur amino acids was achieved; 6 mg l^-1 of cysteamine HCl can be determined in the presence of 11 mg l^-1 of cystamine dihydrochloride. Detection limits are 5 ·1O^-7 M for cysteamine and 1 · 10^-6M for cystamine; as little as 0.012 mg of the thiol and 0.23 mg of the disulfide per litre can be determined. The polarographic behaviour of the cystamine—cysteamine system resembles that described previously for the cysteine— cystine system.     

MP2, DFT and ab initio calculations on thioxanthone

Density functional theory (DFT), HF and MP2 calculations have been carried out to investigate thioxanthone molecule using the standard 6-31+G(d,p) basis set. The results of MP2 calculations show a butterfly structure for thioxanthone. The calculated results show that the predicted geometry can well reproduce the structural parameters. The predicted vibrational frequencies were assigned and compared with experimental IR spectra. A good harmony between theory and experiment is found. The theoretical electronic absorption spectra have been calculated using CIS method. ¹³C and ¹H NMR of the title compound have been calculated by means of B3LYP density functional method with 6-31+G(d,p) basis set. The comparison of the experimental and the theoretical results indicate that density functional B3LYP method is able to provide satisfactory results for predicting NMR properties.     

Voltammetric on-line analysis for some sulphur-containing drugs

Some 2-thiobarbituric acid and thioamide drugs are determined voltammetrically in a flow-through cell. Both direct oxidation in the d.c. mode and cathodic stripping on a mercury-coated glassy carbon electrode are examined for the determination of these drugs. The thiobarbiturie acids can be determined by both methods; the linear range covers 1–2 orders of magnitude with a detection limit in the range 10^-3–10^-6 M depending on the method used and the compound. The thioamides do not plate satisfactorily on the mercury film when operated in the on-line mode and can only be determined by the d.c. anodic oxidation method; the linear range covers at least two orders of magnitude with a detection limit of 5×10^-8–5×10^-7 M depending on the compound.     

Quantum Chemical Study of the Lithium Cation Coordination by Dimethylsulfoxide Molecules

A quantum chemical study of the lithium ion coordination by dimethylsulfoxide molecules has been performed by HF/6-31G (d), HF/6-311+(d,p), and B3LYP/6-311+(d,p) methods with full geometry optimization. The coordination number of Li⁺ in the dimethylsulfoxide was found to be equal to 4. Heats of the complex formation at each stage of the process were calculated (in kJ/mol); these are 267.2, 203.0, 122.8, and 90.5 in HF/6-31G(d); 270.6, 200.5, 108.8, and 82.9 in HF/6-311+(d,p); 256.3, 186.8, 100.8, and 80.1 in B3LYP/6-311+(d,p) for 1-4 DMSO molecules, respectively. The paper reports on the structure parameters of the complexes formed, and the corresponding charge distributions. The solvation of the lithium cation with dimethylsulfoxide molecules was shown to be more preferable than that with water molecules in the gas phase. A possibility for an Li⁺·(4DMSO)·OH^- associate to form in the DMSO medium was examined using the HF/6-311+(d,p) method.     

Molecular structure,vibrational spectra,first order hyper polarizability,NBO and HOMO–LUMO analysis of 4-amino-3(4-chlorophenyl) butanoic acid

The Fourier transform infrared (FT-IR) and Fourier transform Raman (FTR) spectra of 4-amino-3(4-chlorophenyl) butanoic acid were recorded in the regions 4000–400 cm⁻¹ and 4000–100 cm⁻¹, respectively, in the solid phase. Molecular electronic energy, geometrical structure, harmonic vibrational spectra, infrared intensities and Raman scattering activities, highest occupied molecular orbital, lowest unoccupied molecular orbital energy, energy gaps and thermodynamical properties such as zero-point vibrational energies, rotational constants, entropies and dipole moment were computed at the Hartree–Fock/6-31G(d,p) and three parameter hybrid functional Lee–Yang–Parr/6-31G(d,p) levels of theory. The vibrational studies were interpreted in terms of potential energy distribution (PED). The results were compared with experimental values with the help of scaling procedures. Most of the modes have wave numbers in the expected range and are in good agreement with computed values. The first order hyperpolarizability (β_total) of this molecular system and related properties (β, μ, 〈α〉 and Δα) are calculated using HF/6-31G(d,p) and B3LYP/6-31G(d,p) methods based on the finite-field approach. Stability of the molecule arising from hyperconjugative interactions, charge delocalization and intramolecular hydrogen bond-like weak interaction has been analyzed using natural bond orbital (NBO) analysis by using B3LYP/6-31G(d,p) method. The results show that electron density (ED) in the σ1 and π1 antibonding orbitals and second-order delocalization energies E⁽²⁾ confirm the occurrence of intramolecular charge transfer (ICT) within the molecule.