Sequential determination of uranium (IV), free acidity and hydrazine in a single aliquot

A simple analytical procedure for the sequential determination of uranium (IV), free acidity and hydrazine in presence of hydrolysable ions is developed and described. In this method, first, uranium (IV) is determined using fiber optic aided spectrophotometry then same solution is used for determination of free acidity and hydrazine. Free acid is titrated with standard sodium carbonate solution after uranium (IV) is masked with EDTA. Once the end point for the free acid is determined at pH 3.0, an aliquot of formaldehyde is added to liberate the acid equivalent to hydrazine which is then titrated with the same standard sodium carbonate solution using an automatic titration system. The described method is simple, accurate and reproducible. The overall recovery of uranium (IV), nitric acid and hydrazine is 98% with 3% relative standard deviation respectively. The major advantage of the method is that it uses sodium carbonate a primary standard as titrant and generation of corrosive analytical wastes containing oxalate or sulphate is avoided. Valuable metals like uranium and plutonium can easily be recovered from analytical waste before final disposal.     

Potentiometric determination of free acidity in presence of hydrolysable ions and a sequential determination of hydrazine

A simple potentiometric method for the determination of free acidity in presence of hydrolysable ions and sequential determination of hydrazine is developed and described. Both free acid and hydrazine are estimated from the same aliquot. In this method, free acid is titrated with standard sodium carbonate solution after the metal ions in solutions are masked with EDTA. Once the end point for the free acid is determined at pH 3.0, an aliquot of formaldehyde is added to liberate the acid equivalent to hydrazine which is then titrated with the same standard sodium carbonate solution using an automatic titration system. The described method is simple, accurate and reproducible. This method is especially applicable to all ranges of nitric acid and heavy metal ion concentration relevant to Purex process used for nuclear fuel reprocessing. The overall recovery of nitric acid is 98.9% with 1.2% relative standard deviation. Hydrazine content has also been determined in the same aliquot with a recovery of nitric acid is 99% with 2% relative standard deviation. The major advantage of the method is that generation of corrosive analytical wastes containing oxalate or sulphate is avoided. Valuable metals like uranium and plutonium can easily be recovered from analytical waste before final disposal.     

Protolytic equilibria on the surface of carboxyl-containing silica

Potentiometric titration has been used to study the protolytic equilibria on the surface of carboxyl-containing silica (CS) prepared by the reaction of silica (Silokhrom S-80, S_sp = 80 m²/g) with Cl₃SiCH₂CH₂COOCH₃, followed by hydrolysis with 30% sulfuric acid. The titration curve of the vacuum-dried sample is irreversible. The titration curve of its Na⁺ form with hydrochloric acid proceeds lower than the titration curve of its H⁺ form and coincides with the titration curve of the air-dried sample (the last curve is reversible). The titration curve of CS coincides with the titration curve of butyric acid at pH < 6. At pH > 6 the titration curve of CS passes below the titration curve of butyric acid; this is due to the participation of silanol groups on the silica surface in the protolytic equilibria. The pK_a of the grafted CS groups is equal to 4.80 which is close to the pK_a value of butyric acid (4.78). A method has been proposed for the determination of the amount of weak acid groups grafted to the silica. It has been shown that in the titration of CS the equilibrium is established much faster than in the case of the unmodified silica.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 2, pp. 243–247, March–April, 1986.     

Investigation on drying conditions and assays of amidosulfuric acid and sodium carbonate by acidimetric coulometric titration and gravimetric titration

Amidosulfuric acid and sodium carbonate as standards for acid–base titrimetry were assayed by coulometric titration and gravimetric titration. Amidosulfuric acid was directly assayed by coulometric titration with electrogenerated hydroxide ions, and sodium carbonate was assayed by gravimetric back-titration. For sodium carbonate, excess amount of sulfuric acid, whose concentration was determined by coulometric titration, was added to sodium carbonate, and then gravimetrically back-titrated using a sodium hydroxide solution whose concentration was determined by gravimetric titration using the sulfuric acid. The accuracy of the coulometric titration for amidosulfuric acid and sulfuric acid was evaluated by examining the current efficiency of pulse electrolysis, the amount of the electrolysis current used, and the time spent for a titration. In addition, the drying conditions for high purity primary standards have a significant effect on the titration results due to changes in the acid–base assay. The suitable drying conditions for amidosulfuric acid and sodium carbonate were evaluated by mass-change measurements, coulometric titration and gravimetric titration. The measurement uncertainties were estimated from the uncertainties on the titration processes. Finally, the assays of amidosulfuric acid and sodium carbonate were 99.986% ± 0.010% (k = 2) after drying at 50 °C for 2 h, and 99.970% ± 0.016% (k = 2) after drying at 280 °C for 4 h, respectively. In addition, the international consistency was confirmed by measuring certified reference materials (CRMs) available from different National Metrology Institutes, and the compatibility of values among CRMs was experimentally ascertained.     

Determination of polythionates and thiosulphate in mining effluents and mill circuit solutions

A method is described for the determination of total polythionates plus thiosulphate by acidimetric titration. The titration can be carried out either at the Methyl Orange (pH = 4.30) or at the phenolphthalein (pH = 8.20) end-point, with standard sodium hydroxide solution, to determine the amount of acid produced on oxidation of the thiosulphate and polythionates. The precision and accuracy are good and samples containing as little as 0.1 mg of the thio salt can be analysed very easily. Results obtained by this method are compared with those obtained by a calorimetric method and are in good agreement.     

Chemical force titration of plasma polymer-modified PDMS substrates by using plasma polymer-modified AFM tips

Plasma polymerization has gained increasing attention in surface functionalization. We use here chemical force titration to characterize PDMS (polydimethylsiloxane) substrates modified by maleic anhydride-pulsed plasma polymerization. The coating is hydrolyzed to promote the formation of dicarboxylic acid groups. To enhance the variation of the adhesion forces as a function of pH, we use AFM tips modified in the same way as the substrates. The pH-dependent adhesion measurements are performed at different KCl concentrations. The dicarboxylic nature of the maleic acid groups clearly emerges from the force titration curves. The surface pK(a) values (pK(a1) = 3.5 +/- 0.5 and pK(a2) = 9.5 +/- 0.5) of the dicarboxylic acids are evaluated from low electrolyte concentration solutions. The values are shifted toward higher pK(a) values when compared to maleic acid in solution. The first pK(a) appears in the titration force curve for low salt concentration as a peak. This peak changes to a sigmoidal shape at higher salt concentrations. The appearance of a peak is attributed to the formation of strong hydrogen bonds between the tip and the substrate as reported in the literature. The effect of the ionic strength on the force curves is explained by the condensation of counterions on the carboxylate groups. At high pH, the adhesion force almost vanishes. On the approach, at high pH, one first observes repulsion between the tip and the substrate, which varies exponentially with the tip/substrate distance. The decay length of this repulsion force is in good agreement with theoretical predictions of the Debye length, attesting to the electrostatic nature of the interactions. We also find that the replacement of monovalent cation K(+) by the divalent cation Ca(2+) leads to significant changes in the force titration curve at high pH where the dicarboxylic groups are fully ionized. We observe that the adhesion force no longer vanishes at high pH but even slightly increases with pH, an effect that is explained by Ca(2+) ions bridging between two carboxylate groups.     

Analysis of a mixture of a known and an unknown weak acid by titration to a preset pH

The preset-pH titration method has been used to indicate the presence of a second acid when the titration curve (pH vs. volume of added titrant) seems to indicate only one acid. By use of the method even small amounts of propionic acid can be detected in an acetic acid solution despite the small value of Δ log K^H_HA = 0·18. Binary mixtures of acids may bs analysed when one acid is known, and log k^H_HA for the unknown acid may be found. Acetic acid, as the known acid, has been determined together with hydrochloric, mandelic, hydroxyacetic or boric acid or ammonium ion, with an error of about 1%. The method can be used in some cases for titration of ternary mixtures of one known and two unknown acids. Only the sum of the unknown acids can then be determined together with the known acid.     

化学力显微镜对自组装单分子膜的力滴定研究

The concept of force titration was firstly proposed based on the technique of Chemical Force Microscopy (CFM). Self-Assembled Monolayer (SAM) on substrate surface can be titrated with buffer solutions at a nanometer scale by measuring the adhesion force between the SAM-modified substrate and probe tip. The plot of adhesion force vs pH value was termed as force titration curve. As an example, the titration behavior of w-mercaptoundecanoic acid monolayer on gold has been studied. It was found that there is a big hump around pH 5~6 in its force titration curve. Taking the contact angle titration result together, an interaction model for the monolayer was suggested from the chemical hysteresis point of view.     

From decanoate micelles to decanoic acid/dodecylbenzenesulfonate vesicles

Different aspects of mixtures of decanoic acid and sodium decanoate were investigated in aqueous solution up to a total concentration of 300 mM. Depending on the ratio of ionized to nonionized decanoic acid, micelles or vesicles form above the critical concentrations of micelle (cmc) or the critical concentration for vesicle formation (cvc). The micelles and the vesicles are always present together with nonmicellized or nonvesiculized decanoate. The latter was determined for different total concentrations. On the basis of titration curves, by application of the Gibbs phase rule, and on the basis of differential scanning calorimetry measurements and an electron microscopy analysis, the pH region within which vesicles exist was identified (pH 6.8-7.8). At pH 7.0, the concentration of nonvesiculized decanoate is approximately 20 mM. Decanoic acid/decanoate vesicles can be sized down by the extrusion technique to form stable and mainly unilamellar vesicles with a mean diameter of less than 100 nm. By coaddition of an equimolar amount of sodium dodecylbenzenesulfonate (SDBS) to decanoic acid, vesicles also formed below pH 6.8. These mixed vesicles were investigated as potential templates for the peroxidase-catalyzed polymerization of aniline at pH 4.3. Furthermore, decanaote micelles (at pH 11.0) were applied as reaction modifiers for the simultaneous competitive alkaline hydrolysis of p-nitrophenylacetate and fluorescein diacetate. While the rate of hydrolysis of fluorescein diacetate is slowed considerably in the presence of the micelles in comparison with the micelle-free system, the rate of hydrolysis of p-nitrophenylacetate remains almost unaffected.     

Copper(II) ion hydrolysis in aqueous solution

A copper(II) ion-selective-electrode potentiometric method was used to determine the first and second hydrolysis constants of Cu²⁺. Special techniques prevented copper(II) hydroxide precipitation, and copper(II) carbonate and cipper(II) organic complexation during the titration of the experimental solution over the pH range 6.8–8.4. The large change in the total copper concentration during the titration due to adsorption of copper onto the vessel walls was accounted for by measuring the total copper concentration at each pH by atomic absorption spectrophotometry. The two hydrolysis constants were determined at 25°C in 0.7 and 0.05m NaClO₄ media. The measured stability constants are independent of the copper concentration and yield similar zero ionic strength values. Also, the stepwise equilibrium constants decrease as the ligand number increases.     

Comparison of a single-use pH test strip and a glass electrode for potentiometric titration

The potentiometric titration of a carbonate mixture or an acetate solution is a common experiment in analytical laboratories. Typically, a glass electrode combined with a calomel or Ag/AgCl reference electrode is used to locate the equivalence points in neutralization titrations. The dissociation constants of weak acids and bases can be calculated from the pH at the half-neutralization point. Recently, a new commercial product for measuring pH has been developed. This novel acid–base detection strip is a single-use sensor that requires neither storage in a preservation liquid nor calibration prior to use. This study examined its suitability for the continuous monitoring of pH changes in potentiometric titrations of carbonate mixtures, acetate solutions, or ammonia solutions. There were no significant differences in the concentrations of solutions tested using a glass electrode and a pH test strip. The pK_a, pK_b, and pH values determined using the two systems differed by less than 5%. The results confirmed that the pH strips are suitable for continuously monitoring pH changes during neutralization titrations. However, the strips can only be used once.     

Application of the two stage ascorbic acid-iodate titration to the determination of iodine and iodide

Summary An extension of the two stage titration of ascorbic acid against iodate to the determination of iodine and iodide in a solution is described. A known excess of ascorbic acid, standardized against iodate, is added to a mixed iodine and iodide solution and the excess ascorbic acid together with the total iodide is titrated against the same iodate to the two end points under controlled conditions of acidity. The differential method of calculation gives the amount of iodine and iodide with a blank and a direct titration. The accuracy of the results provides a useful evidence for the mechanism suggested for the two stage titration of ascorbic acid against iodate.Our sincere thanks are due to Professor S. S. Joshi for kind interest in the work.     

电位滴定测定富锂锰基正极材料中锰

采用盐酸、硝酸溶解样品,加入焦磷酸钠溶液并调节溶液pH为6.0~7.0。用高锰酸钾标准溶液滴定至电位滴定仪上,根据消耗的高锰酸钾标准溶液的体积计算样品中的锰含量。探究了焦磷酸钠用量、溶液pH、共存元素等对测定锰含量的影响。在最优的实验条件下,方法的相对标准偏差在0.13%~0.22%之间,加标回收率在99.8%~100.5%之间。本方法是富锂锰基正极材料中质量分数10%~60%的锰测定的理想方法。     

Determination of total carbon dioxide in seawater by capillary type isotachophoresis

Summary A new analytical procedure for total carbon dioxide in seawater was developed: a capillary-type isotachophoresis which applied a tubular microporous PTFE membrane as a preliminary enrichment was used. Carbon dioxide was generated by adding sulfuric acid to seawater samples, permeated through a tubular microporous PTFE membrane and dissolved in sodium hydroxide solution for the separation from large amounts of coexisting anions, such as chloride and sulfate ions. A linear working curve was obtained for artificial seawater samples containing up to 40 mg/l of total carbon dioxide. The proposed method was applied to the determination of total carbon dioxide in surface and bottom seawater samples. Concentrations of the total of free carbon dioxide and carbonic acid, hydrogencarbonate and carbonate ions in these samples were calculated from the concentration of total carbon dioxide, temperature, pH and salinity of samples measured in situ.

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Bestimmung von Gesamtkohlendioxid in Meereswasser durch Capillar-Isotachophorese

     

Conformational transition of the copolymer of maleic acid and styrene in aqueous solution. II

The temperature dependence of the conformational transition from a compact to expanded-coil form of the alternating copolymer of maleic acid with styrene in aqueous 0.03M NaCl solution was studied at 15 to 40°C by pH titration, optical titration, and calorimetric measurements. The pH titration curve scarcely changed with temperature. The degree of dissociation of primary carboxyl groups in the copolymer at the midpoint of the conformational transition, determined by the optical titration, was almost independent of temperature. The standard enthalpy change of the transition at 25°C estimated from the calorimetric data was 0.36₃ kcal/mole, which may mean that the difference between the standard free energy changes of the transition at 20°C and 40°C does not exceed experimental error. The enthalpy change agrees well with the heat of transfer of benzene from the hydrophobic to the aqueous medium, and thus the compact form of the copolymer is considered to be stabilized by the hydrophobic interaction between the phenyl residues in the interior of the molecule.     

固定pH滴定法测定弱酸弱碱性药物

报道一种水溶液吕测定弱酸弱碱性药物的新型滴定分析方法－固定ｐＨ滴定法，其理论基础是弱酸弱碱在水溶液中各种存在形式的分布系数在ｐＨ值固定时为常数，对甲硝唑，盐酸美西律等离散常数在１０＾－８至１０＾－１１范围内的７种弱酸弱碱性药物进行测定。结果与药典法吻合，回收率在９９．４％～１００．６％，方法简便，快速，准确，制剂中的赋形剂及色物不影响测定。     

Ammonium uranyl carbonate (AUC) based process of simultaneous partitioning and reconversion for uranium and plutonium in fast breeder reactors (FBRs) fuel reprocessing

Ammonium uranyl carbonate (AUC) based process of simultaneous partitioning and reconversion for uranium and plutonium is developed for the recovery of uranium and plutonium present in spent fuel of fast breeder reactors (FBRs). Effect of pH on the solubility of carbonates of uranium and plutonium in ammonium carbonate medium is studied. Effect of mole ratios of uranium and plutonium as a function of uranium and plutonium concentration at pH 8.0–8.5 for effective separation of uranium and plutonium to each other is studied. Feasibility of reconversion of plutonium in carbonate medium is also studied. The studies indicate that uranium is selectively precipitated as AUC at pH 8.0–8.5 by adding ammonium carbonate solution leaving plutonium in the filtrate. Plutonium in the filtrate after acidified with concentrated nitric acid could also be precipitated as carbonate at pH 6.5–7.0 by adding ammonium carbonate solution. A flow sheet is proposed and evaluated for partitioning and reconversion of uranium and plutonium simultaneously in the FBR fuel reprocessing.     

Linear titration plots for the analysis of mixtures of three weak acids or bases

Linearly related functions have been derived which enable mixtures of three weak acids or bases in solution to be analysed by means of pH-titration data. This theory has been tested with data from the titration of a variety of mixtures of acids. The data required for the functions are pH, volume of titrant, the equilibrium constants relevant to the mixture, and an independently determined equivalence volume. This may be the equivalence volume for one of the components of the mixture or the sum of the equivalence volumes for any two or all three of the components. It is immaterial how this equivalence volume is obtained, but it is usually possible to obtain the total equivalence volume from data in another part of the same titration curve (when a large excess of titrant has been added).     

Assessment of two theoretical methods to estimate potentiometric titration curves of peptides: comparison with experiment

We compared the ability of two theoretical methods of pH-dependent conformational calculations to reproduce experimental potentiometric titration curves of two models of peptides: Ac-K5-NHMe in 95% methanol (MeOH)/5% water mixture and Ac-XX(A)7OO-NH2 (XAO) (where X is diaminobutyric acid, A is alanine, and O is ornithine) in water, methanol (MeOH), and dimethyl sulfoxide (DMSO), respectively. The titration curve of the former was taken from the literature, and the curve of the latter was determined in this work. The first theoretical method involves a conformational search using the electrostatically driven Monte Carlo (EDMC) method with a low-cost energy function (ECEPP/3 plus the SRFOPT surface-solvation model, assumming that all titratable groups are uncharged) and subsequent reevaluation of the free energy at a given pH with the Poisson-Boltzmann equation, considering variable protonation states. In the second procedure, molecular dynamics (MD) simulations are run with the AMBER force field and the generalized Born model of electrostatic solvation, and the protonation states are sampled during constant-pH MD runs. In all three solvents, the first pKa of XAO is strongly downshifted compared to the value for the reference compounds (ethylamine and propylamine, respectively); the water and methanol curves have one, and the DMSO curve has two jumps characteristic of remarkable differences in the dissociation constants of acidic groups. The predicted titration curves of Ac-K5-NHMe are in good agreement with the experimental ones; better agreement is achieved with the MD-based method. The titration curves of XAO in methanol and DMSO, calculated using the MD-based approach, trace the shape of the experimental curves, reproducing the pH jump, while those calculated with the EDMC-based approach and the titration curve in water calculated using the MD-based approach have smooth shapes characteristic of the titration of weak multifunctional acids with small differences between the dissociation constants. Nevertheless, quantitative agreement between theoretically predicted and experimental titration curves is not achieved in all three solvents even with the MD-based approach, which is manifested by a smaller pH range of the calculated titration curves with respect to the experimental curves. The poorer agreement obtained for water than for the nonaqueous solvents suggests a significant role of specific solvation in water, which cannot be accounted for by the mean-field solvation models.     

多元校正流动注射电位滴定法同时测定苯甲酸和山梨酸

将流动注射应用于酸碱电位滴定分析,建立了一种可同时测定混合有机酸的电位滴定新方法。在该方法中,用氢氧化钠与氯化钾的混合溶液作为滴定剂,在流通池中同时插入pH指示电极和氯离子指示电极,在滴定过程中的任一滴定点,流出液的pH值和酸碱的混合比例可由两个电极的电位测定值同时获得,从而可应用多元校正法由相应的滴定曲线求得混合酸中每一种组分的含量。该方法不仅免去了体积和时间读数,而且减少了试剂和样品的消耗量,分析速度快。应用该方法对混合样品中的苯甲酸和水杨酸进行同时测定,其相对标准偏差分别为0．19％～0．37％,回收率分别为97．3％～102．6％。