Microwave desolvation for acid sample introduction in inductively coupled plasma atomic emission spectrometry

This study deals with the behaviour of a microwave desolvation system (MWDS) with acid solutions in inductively coupled plasma atomic emission spectrometry. Hydrochloric, nitric, sulphuric and perchloric acids at different concentrations (up to 0.6 mol l⁻¹) have been tested. Sample uptake rate (Q_l) was also varied. The parameters evaluated for each variable were analyte and solvent transport rates and emission intensity. The combination of low acid concentrations (0.05–0.1 mol l⁻¹) and low liquid flows (0.4 ml min⁻¹) leads to the highest analyte transport rate and emission signal and to the lowest solvent transport rate. For Q_l higher than 1.9 ml min⁻¹, the use of an impact bead is advisable. Among the acids tested, sulphuric and perchloric acids give rise to higher emission intensities than hydrochloric acid and nitric acid. Nonetheless, the limits of detection (LODs) obtained with the MWDS are about the same magnitude irrespective of the solution employed. The LODs reached when using the MWDS are similar to those obtained with a desolvation system based on infrared heating of the aerosol.     

The reaction of Se(IV) with 2-aminodiphenylamine and its application to spectrophotometric determination of selenium in a strongly acidic medium

Se(IV) reacts with 2-aminodiphenylamine in perchloric, sulphuric or hydrochloric acid media to give the phenylbenzoselen-adiazolium cation. The optimum hydrogen-ion concentration ranges from about 0.1 to 5M. The molar absorptivity at =352 nm is 1.81×10⁴ 1 · mole^–1 · cm^–1. The product is extracted as an ion-association complex with perchlorate into a mixture of hexanol and chlorobenzene. The kinetics of the reaction was investigated.     

Radiolysis of 1-naphthol in aqueous solutions

The effects of absorbed doses, initial pH and 1-naphthol concentration onto its radiolysis in aqueous sulphuric and hydrochloric acids by gamma rays from ⁶⁰Co were investigated. Under the experimental conditions, 1-naphthol degradation yields increased with increasing the absorbed doses (0.3–3.0 kGy) and with decreasing the initial 1-naphthol concentration (20–1 ppm). It was found out that the hydrated electrons did not play any significant roles in 1-naphthol radiolysis, as the degradation yields were higher at pH₀ ~ 0.46 compared to those at pH₀ ~ 2.0–5.0. The corresponding radiolytic yields G(−1-naphthol) were (6.13 ± 1.00)) × 10⁻² and (5.11 ± 0.22) × 10⁻² μmol/J in sulphuric acids, (15.61 ± 3.85) × 10⁻² and (4.76 ± 0.48) × 10⁻² μmol/J in hydrochloric acids. 1-Naphthol degradation rates could be described by the kinetic equations of pseudo-first-order reactions. An empirical relation between the observed reaction constants k _D and the initial 1-naphthol concentrations was established, enabling to predict the absorbed doses required for a given treatment efficiency. Three products of 1-naphthol degradation were revealed using an HPLC/UV procedure.     

The elimination kinetics and mechanisms of ethyl piperidine‐3‐carboxylate,ethyl 1‐methylpiperidine‐3‐carboxylate,and ethyl 3‐(piperidin‐1‐yl)propionate in the gas phase

The gas‐phase elimination kinetics of the above‐mentioned compounds were determined in a static reaction system over the temperature range of 369–450.3°C and pressure range of 29–103.5 Torr. The reactions are homogeneous, unimolecular, and obey a first‐order rate law. The rate coefficients are given by the following Arrhenius expressions: ethyl 3‐(piperidin‐1‐yl) propionate, log k₁(s^?1) = (12.79 ± 0.16) ? (199.7 ± 2.0) kJ mol^?1 (2.303 RT)^?1; ethyl 1‐methylpiperidine‐3‐carboxylate, log k₁(s^?1) = (13.07 ± 0.12)–(212.8 ± 1.6) kJ mol^?1 (2.303 RT)^?1; ethyl piperidine‐3‐carboxylate, log k₁(s^?1) = (13.12 ± 0.13) ? (210.4 ± 1.7) kJ mol^?1 (2.303 RT)^?1; and 3‐piperidine carboxylic acid, log k₁(s^?1) = (14.24 ± 0.17) ? (234.4 ± 2.2) kJ mol^?1 (2.303 RT)^?1. The first step of decomposition of these esters is the formation of the corresponding carboxylic acids and ethylene through a concerted six‐membered cyclic transition state type of mechanism. The intermediate β‐amino acids decarboxylate as the α‐amino acids but in terms of a semipolar six‐membered cyclic transition state mechanism. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 106–114, 2006     

Reaction of Amino Acids,Di‐ and Tripeptides with the Environmental Oxidant NO3.: A Laser Flash Photolysis and Computational Study

Absolute rate coefficients for the reaction between the important environmental free radical oxidant NO₃^. and a series of N‐ and C‐protected amino acids, di‐ and tripeptides were determined using 355 nm laser flash photolysis of cerium(IV) ammonium nitrate in the presence of the respective substrates in acetonitrile at 298±1 K. Through combination with computational studies it was revealed that the reaction with acyclic aliphatic amino acids proceeds through hydrogen abstraction from the α‐carbon, which is associated with a rate coefficient of about 1.8×10⁶ m ^?1 s^?1 per abstractable hydrogen atom. The considerably faster reaction with phenylalanine [k=(1.1±0.1)×10⁷ m ^?1 s^?1] is indicative for a mechanism involving electron transfer. An unprecedented amplification of the rate coefficient by a factor of 7–20 was found with di‐ and tripeptides that contain more than one phenylalanine residue. This suggests a synergistic effect between two aromatic rings in close vicinity, which makes such peptide sequences highly vulnerable to oxidative damage by this major environmental pollutant.     

Synthesis of polymers containing azo groups in the main chain from <Emphasis Type="Italic">m</Emphasis>-phenylenediamine: Study of doping

Synthesic approach to polymers containing azo groups was developed on the basis of diazotization and azo-coupling reaction of m-phenylenediamine (m-PDA) with various ratio m-phenylenediamine-sodium nitrite. Doping of poly(azoaminophenylenes) with iodine, perchloric and hydrochloric acids was examined. Electroconductivity increases in the case of iodine to 0.2 S mol⁻¹, of perchloric acid, to 7×10⁻³ S mol⁻¹, and at the action of hydrogen chloride it is virtually unaffected. According to the ESR spectra, at the doping with iodine and perchloric acid electroconductivity enhances generally due to the mobility increase of the charge carriers (polarons).     

Determination of selenium in human tissues by atomic absorption spectrometry

A simple method is described for the determination of selenium in human tissues without the use of perchloric acid. Digestion with nitric and sulphuric acids is followed by hydride generation and atomic absorption spectrometry. Results for NBS bovine liver and IAEA horse kidney reference materials were in good agreement with assigned concentrations, as was also achieved with the perchloric acid digestion. Recovery of added selenium was >90%, and the relative standard deviation was 5.5% for within-batch and 6.9% for between-batch analyses. The values of selenium in heart tissue were 0.9–1.3 μg g^?1 dry weight.     

The conditions for quantitative precipitation of phosphate as ammonium 12-molybdophosphate

The radionuclide phosphorus-32 has been usud to measure the effects of (I) temperature, (2) time of standing, (3) stirring, (4) the molybdate-phosphate ratio, (5) hydrochloric, sulphuric, nitric and perchloric acids, and (6) ammonium nitrate on the efficiency of precipitation of ammonium l 2-molybdophosphate,The precipitate is formed quantitatively after 30 min at any temperature between 50° and 80° followed by 30 min at room temperature' provided that the liquid is stirred at 15-min intervals. Twice the stoichiometric amount of nitromolybdate reagent is sufficient for quantitative precipitation. Nitric add is essential ; perchloric acid does not interfere, but hydrochloric and sulphuric acids do. Ammonium nitrate does not affect the efficiency of the precipitation,     

The kinetics of the oxidation of cyclopentanone with decaneperoxysulfonic acid

The kinetics of the oxidation of cyclopentanone with decaneperoxysulfonic acid at 291–323 K in CCl₄ has been studied. The reaction is not autocatalytic, and its rate increases linearly with increases in the concentrations of each of the reagents. The addition of CF₃COOH does not affect the reaction rate. The observed results are explained within a scheme which is a special case of the well-known Baeyer-Villiger reaction mechanism established for peroxycarboxylic acids. The effective rate constant of the process has been determined: logk (L mol⁻¹ s⁻¹)=(7.6±1.7) — (42.1±9.6)/θ, where θ=2.30RT kJ mol⁻¹. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1827–1829, October, 1993.     

Kinetic study of some reactions related to the Mn(II)-catalyzed bromate-saccharide oscillating reactions

In the stirred batch experiment, the Mn(II)-catalyzed bromate-saccharide reaction in aqueous H₂SO₄ or HClO₄ solution exhibits damped oscillations in the concentrations of bromide and Mn(II) ions. Peculiar multiple oscillations are observed in the system with arabinose or ribose. The apparent second-order rate constants of the Mn(III)-saccharide reactions at 25°C are (0.659, 1.03, 1.76, 2.32, and 6.95) M⁻¹ s⁻¹ in 1.00 M H₂SO₄ and (4.69, 7.51, 10.2, 13.5, and 36.2) M⁻¹ s⁻¹ in (2.00–4.00) M HClO₄ for (glucose, galactose, xylose, arabinose, and ribose), respectively. At 25°C, the observed pseudo-first-order rate constant of the Mn(III)-Br⁻ reaction is k_obs = (0.2 ± 0.1) [Br⁻] + (130 ± 5)[Br⁻]² + (2.6 ± 0.1) × 10³[Br⁻]³ + (1.2 ± 0.2) × 10⁴[Br⁻]⁴ s⁻¹ and the rate constant of the Br₂ Mn(II) reaction is less than 1 × 10⁻⁴ M⁻¹ s⁻¹. The second-order rate constants of the Br₂-saccharide reactions are (3.65 ± 0.15, 11.0 ± 0.5, 4.05, 12.5 ± 0.7, and 2.62) × 10⁻⁴ M⁻¹ s⁻¹ at 25°C for glucose, galactose, xylose, arabinose, and ribose, respectively.