Determination of fluoride and oxalate using the indicator reaction of Zr(IV) with methylthymol blue adsorbed on silica gel

Solid-phase spectrophotometric and visual test-methods of fluoride and oxalate determination are proposed. The methods are based on the competitive reactions of ZrOCl₂ with methylthymol blue immobilized on silica gel and fluoride or oxalate in solution. Absorbance of the solid-phase reagent at 590 nm decreases with the growth of fluoride and oxalate contents in solution. The developed methods demonstrate high selectivity. The interference of Bi(III) and SO₄²⁻, PO₄³⁻ is eliminated by the addition of 0.01 mol L⁻¹ solution of ascorbic acid and 0.01 mol L⁻¹ of BaCl₂, respectively. To eliminate the fluoride interference with oxalate determination 1 × 10⁻³ mol L⁻¹ solution of Ca(NO₃)₂ at pH 1.5 was added. The anions of the organic acids were destructed prior to F⁻ determination by ultrasonic exposition (44 kHz, intensity of ≤10 W cm⁻² for 3 min). The proposed methods were applied to the analysis of mineral water, toothpaste and biological fluids.     

Multiply Charged Anions,Maximum Charge Acceptance,and Higher Electron Affinities of Molecules,Superatoms,and ClustersSCI北大核心CSCD

The addition of electrons to form gas-phase multiply charged anions (MCAs) normally requires sophisticated experiments or calculations.In this work, the factors stabilizing the MCAs, the maximum electron uptake of gas-phase molecules, X, and the electronic stability of MCAs X^Q-, are discussed. The drawbacks encountered when applying computational and/or conceptual density functional theory (DFT) to MCAs are highlighted. We develop and test a different model based on the valence-state concept. As in DFT, the electronic energy, E(N, v_ex), is a continuous function of the average electron number, N, and the external potential, v_ex, of the nuclei. The valence-state-parabola is a second-order polynomial that allows extending E(N, v_ex) to dianions and higher MCAs. The model expresses the maximum electron acceptance, Q_max, and the higher electron affinities, A_Q, as simple functions of the first electron affinity, A₁, and the ionization energy, I, of the "ancestor" system. Thus, the maximum electron acceptance is Q_{max, calc} = 1 + 12A₁/7(I -A₁). The ground-state parabola model of the conceptual DFT yields approximately half of this value, and it is termed Q_{max, GS} = ${}^{1}\!\!\diagup\!\!{}_{2}\; $ + A₁/(I -A₁). A large variety of molecules are evaluated including fullerenes, metal clusters, super-pnictogens, super-halogens (OF₃), super-alkali species (OLi₃), and neutral or charged transition-metal complexes, AB_mL_n^0/+/-. The calculated second electron affinity A_{2, calc} = A₁-(7/12)(I -A₁) is linearly correlated to the literature references A_{2, lit} with a correlation coefficient R = 0.998. A₂ or A₃ values are predicted for further 24 species. The appearance sizes, n_ap^3-, of triply charged anionic clusters and fullerenes are calculated in agreement with the literature.     

用低通滤波法处理内燃机缸内流动的LDA测量数据

本文根据内燃机缸内流动的LDA测量数据的特点，讨论了低通滤波过程、数据预处理过程、截止频率的选择、数据处理误差等，论述了在目前LDA测量数据率还不够高的情况下，如何较好地用低通滤波法对LDA测量数据进行单一循环分析处理，最大限度地减少数据处理误差．     

CONVERGENCE RESULTS FOR NON-OVERLAP SCHWARZ WAVEFORM RELAXATION ALGORITHM WITH CHANGING TRANSMISSION CONDITIONS

In this paper,we establish a new algorithm to the non-overlapping Schwarz domain decomposition methods with changing transmission conditions for solving one dimensional advection reaction diffusion problem.More precisely,we first describe the new algorithm and prove the convergence results under several natural assumptions on the sequences of parameters which determine the transmission conditions.Then we give a simple method to estimate the new value of parameters in each iteration.The interesti...     

Xylenol orange adsorbed on silica surface as a solid phase reagent for lead determination using diffuse reflectance spectroscopy

The solid-phase reagents on the base of xylenol orange and its complex with Fe(III) immobilized on silica surface were obtained. The interaction of Pb(II) with developed reagents was studied. The conditions of quantitative recovery of Pb(II) from diluted solutions, such as acidity of aqueous phase, the amount of the sorbent, the volume of solutions and the time of equilibrium reaching, were examined. The tolerance limits of metal ions in the sorption of Pb(II) at pH 4.5-5.5 are reported. The capabilities of immobilized xylenol orange for Pb(II) pre-concentration prior to its diffusion reflectance spectroscopic detection was evaluated. The detection limit was 2 mug l(-1). The developed method was applied to Pb(II) determination in natural water and foodstuffs.     

Test Determination of Lead and Zinc in Water with the Use of Xylenol Orange Immobilized on Silica

Xylenol Orange immobilized on silica as a complex of iron(III) was used for the test determination of lead(II) and zinc(II) in drinking water over concentration ranges of 10–100 and 13–130 g/L, respectively. The maximum distribution coefficients were found to be 7.50 × 10³ mL/g for Pb and 3.75 × 10³ mL/g for Zn. The macro main trace components of water at a level of their maximum permissible concentrations caused no interference. Al(III), Fe(III), and Zn(II) in the presence of NH₄F did not interfere with the determination of Pb(II), whereas lead in the presence of acetate caused no interference with the determination of Zn(II).