Binding of fluoride and carbonate by open chain polyammonium cations

The formation of open chain polyammonium cation-fluoride and -carbonate complexes was studied by potentiometric and calorimetric techniques at t=25 °C. Several species of H_iAL (A=amine; L=F⁻, CO₃²⁻) are formed in both systems with a mean stability (ζ=|z_anion×z_cation|) and for fluoride and carbonate, respectively. The comparison with analogous systems (chloride and acetate for fluoride and hydrogenphosphate, sulfate and malonate for carbonate) showed that fluoride and carbonate form the most stable species with open chain polyammonium cations, among low molecular weight anions. The N-alkyl substitution does not play negligible role in the stability of these complexes, the species formed by substituted amines being more stable.     

用氟离子电极对土壤中铝作直接电位法测定

本文提出用氟离子电极对土壤中铝作直接电位法测定。大大减少了以往的用终点电位滴定法测定土壤中铝含量的实验步骤与时间,并较大地提高了测定的准确度。方法是取一定量的土壤试液加入到pH为5,离子强度为1.0的缓冲溶液中,再加入一定量的F~-离子标液,让F~-与Al_(3 )络合稳定后,用氟离子电极测出溶液中的游离态F~-浓度,从而计算出Al~(3 )的总浓度。     

氟离子-乳酸-丙酮-Mn~(2+)-BrO_3~--H_2SO_4振荡反应及其在分析中的应用

氟离子对乳酸-丙酮-Mn~(2+)-BrO_3~--H_2SO_4化学振荡反应的周期和振幅有显著的影响,F~-的浓度在8.00×10~(-5)～1.00×10~(-3)mol·L~(-1)范围内与振荡反应周期的改变值△t_p和振幅的改变值△H均有良好的线性关系,是一线性范围宽、灵敏度高的动力学分析测试体系。获得振荡反应诱导期、周期的表观活化参数E_(in)、E_p分别为55.71 kJ·mol~(-1)、67.41 kJ·mol~(-1),探索了该振荡体系可能的反应机理。     

Extraction-Spectrophotometric Determination of Fluoride Using N-Phenylbenzohydroxamic Acid

Abstract

Fluoride gives a very stable complex with scandium and, hence, by determining the unreacted scandium, the fluoride content can be calculated. Excess scandium is reacted with an ethanolic solution of N-benzoylphenylhydroxylamine (BPHA) at pH 6.0, and the scandium-BPHA complex is extracted into isoamyl alcohol. Scandium is determined spectrophotometrically after adding xylenol orange. Beer's law for fluoride is obeyed in the range of 0.05 –1.5 ppm; the molar absorptivity is 1.94×10⁴ 1 mol^?1 at 565 nm. The procedure is applicable for the determination of fluoride in various types of samples.     

Interferences elimination in ion chromatography by inclusion of the interfering ion into the mobile phase—Analysis of fluoride in chloride rich dietary samples

New approach to the chloride interferences elimination by addition of the interfering ion to the mobile phase is proposed and evaluated. Different eluents for the non-suppressed ion chromatographic analysis of fluorides in chlorides rich samples were tested and compared with eluent recommended by the column manufacturer. The limit of detection, linearity range and resistance to matrix effects caused by chlorides were the comparison criteria. The applicability of the selected eluent was demonstrated through the analysis of the edible salts and various tea samples. The employment of the proposed eluent shorten the time of the analysis since the only required preparation steps for edible salts were the dissolution and appropriate dilution of the samples. The recovery test was employed to verify the obtained results.     

Studies on fluoride adsorption capacities of amorphous Fe/Al mixed hydroxides from aqueous solutions

This study evaluated the effectiveness of amorphous iron and aluminum mixed hydroxides in removing fluoride from aqueous solutions. A series of mixed Fe/Al samples were prepared at room temperature by co-precipitating Fe and Al mixed salt solutions at pH 7.5. The compositions (Fe:Al molar ratio) of the oxides were varied as 1:0, 3:1, 2:1, 1:1 and 0:1 and the samples were characterized by XRD, BET surface area and pH_ZPC. The XRD studies indicated the amorphous nature of the samples and Al(III) incorporation on Fe(III) hydroxides. Batch adsorption studies for fluoride removal on these materials showed that the adsorption capacities of the materials were highly influenced by solution pH, temperature and initial fluoride concentration. The rate of adsorption was fast and equilibrium was attained within 2 h. The adsorption followed first-order kinetics with intraparticle diffusion as the rate determining step for all the samples. The experimental data fitted well to both Langmuir and Freundlich adsorption isotherms. All samples exhibited very high Langmuir adsorption capacities; the sample with molar ratio 1 has shown maximum adsorption capacity of 91.7 mg/g. The thermodynamic parameters were determined to study the feasibility of the adsorption process.     

Synthesis of a chitin-based biocomposite for water treatment: Optimization for fluoride removal

The optimum composition of a chitin-based biocomposite was determined based on both its fluoride adsorption capacity and its chemical resistance in acid aqueous solution. Parameters such as the chitin content, additive content, catalyst content, chitin particle size, degree of acetylation of chitin and effect of pH on adsorption were evaluated. It was possible to chemically reinforce chitin while keeping an acceptable fluoride adsorption capacity onto the chitin-based biocomposites. Optimum chitin content (60%) was limited by the polymer-biopolymer anchoring capacity. An amine-based additive was used to improve the biocomposite adsorption capacity; however, its inclusion was not suitable in terms of biocomposite chemical resistance. The chitin particle size had no effect on adsorption capacity, and the degree of acetylation of chitin notably modified biocomposite adsorption capacity. On the other hand, the biocomposite chemical resistance was notably improved compared to pure chitin. The physicochemical properties of the optimum chitin-based biocomposite showed its potential for being used in continuous adsorption processes.     

Efficient colorimetric fluoride anion chemosensors based-on simple naphthodipyrrolidone dyes

Two novel lactam-containing compounds based on simple naphthodipyrrolidones have been developed as colorimetric sensors for fluoride anion with high selectivity and sensitivity. The two compounds can selectively act with fluoride anion and exhibit the naked-eye visible color change from purple to blue, and the detection limit could reach the concentration as low as 3.0 × 10^?6 M. The proton nuclear magnetic resonance titrations reveal the happen of intermolecular proton transfer between the hydrogen atom on the lactam N and the fluoride anion. Quantum chemical calculations indicate that the deprotonation can alleviate the distorted degree between the peripheral phenyl and the naphthodipyrrolidone core, and raise the frontier molecular orbital energy levels and decrease the band gap, rendering the protonated molecules a new more batho-chromic absorption band.