用卡尔曼滤波作非平衡电位滴定

用长链四烷基锡为中性载体制备了性能优良的十二烷基磺酸根PVC膜电极。用其为指示电极,以非平衡方式进行快速电位滴定。借卡尔曼滤波方法可靠地确定等当点。引入的滤波算法具有通用性,能有效地节省电位滴定分析时间。     

Titrations with piezoelectric monitoring : Part 2. Compleximetric titrations and precipitation titrations

A piezoelectric detector is used to monitor titration reactions involving complex formation or precipitation. Analytes at concentrations down to 10^?4 mol 1^?1 can be determined. The frequency shift in the compleximetric titrations is affected by the composition of the solution, the buffer and competing ligands present in the solution. Factors influencing the frequency shift in the precipitation titration are also investigated.     

A pH-stat study of the reaction of some transition metal cations with disodium ethylenedinitrilotetraacetate (EDTA) and its analytical application

The pH-stat titration technique is an autonomous and very powerful tool for performing and monitoring chelatometric titrations of metal cations with great accuracy, poorly known, however, and seldom exploited. Based on measurement of the amount of strong base required to keep the pH of the test solution at a selected value during stepwise known additions of ethylenedinitrilotetraacetate (EDTA), it requires a glass electrode as the only sensor and is easily implemented on potentiometric titrators. It was introduced a quarter of century ago on an empirical basis for a very peculiar purpose (determination of calcium in diary products), but only very recently it was generalised and its fundamentals were thoroughly examined. In this work, pH-static titrations of some transition metal cations of analytical relevance (Co²⁺, Cu²⁺, Mn²⁺, Zn²⁺) were thoroughly investigated in the acid pH range between 2.3 and 5 or 7 (the highest pH depending on the metal hydroxide or carbonate solubility). The results at higher acidity showed unsuspected properties of such chelation reactions. At moderately acid pH (generally ≥4), indeed, pH-static titrations yield results of high precision and accuracy. On decreasing pH, however, the reaction stoichiomety deviates more and more from the 1:1 ratio between chelating agent and cation, seemingly because of formation of binuclear complexes, an occurrence very seldom mentioned in the current literature. The optimal titration conditions for each metal are defined, and directions for establishing a laboratory protocol for quantitative determinations are given.     

Electrometric titrations with two polarized second-order electrodes

Electrometric titrations at constant resistance with two polarized second-order electrodes are shown to be possible. The polarization curve of the silver/silver chloride electrode is investigated theoretically and experimentally in order to find the best conditions for chloride titrations.Directions are given for the preparation and manipulation, of electrodes which enable quick titrations with rather dilute standard solutions (up to 0.001N AgNO₃). The titration apparatus used and some practical applications of the amperometric titration are described.     

Multiple anion binding by a zinc-containing tetratopic cyclen-resorcinarene

The synthesis and binding properties of a new tetratopic anion receptor are reported. The resorcinarene ligand bearing four cyclen moieties is able to bind four Zn²⁺ ions and subsequently bind anions. NMR titrations show proton shifts during the binding of the first one or two anions. Isothermal titration calorimetry (ITC) titrations show that two or more anions bind to one tetramer. The tetratopic receptor in methanol has high affinity for dihydrogen phosphate, acetate, and halide ions and weak affinity for nitrate and perchlorate.     

Magnetic titrations

Magnetic titrations using a new titration cell and procedure are described. The paramagnetism of a hexammine nickel nitrate solution decreases linearly upon the addition of cyanide up to the endpoint (complete formation of Ni(CN)₄^2-) ; there is no evidence of the formation of intermediate complexes. Intermediate complexes are evident in the titrations of iron(II) with 1,10-phenanthroline and with 2,2'-bipyridyl; log K₁ values, calculated from the magnetic data, are 6.0 and 5.0 respectively.     

Miniglass,an interactive program for the evaluation of stability constants of metal/ligand complexes from potentiometric data

MINIGLASS is a microcomputer program for the treatment of pH titrations for evaluation of stability constants and adjustment of the parameters defining the titration curve. The program is written in PASCAL for the HP-200 computer series, and contains procedures for blank titrations, acidity constants and metal/ligand stability constants. Graphics support is provided for easy interaction with the user. The data files can be written by the editor of the operating system or can be created automatically from an automatic titration system. The program is tested for the determination of the formation constants of the well-studied Ni²⁺/glycine system. The results obtained agree well with literature values.     

End-point construction and systematic titration error in linear titration curves-precipitation reactions

The systematic titration error which is introduced by the intersection of tangents to hyperbolic titration curves is discussed for precipitation reactions. A simple expression for the systematic titration error is derived, and S/C_x² is proposed as a measure of the sharpness of the titration curve. The effects of the conditional solubility product (S), the concentration of the unknown component (C_x), and the ranges used for the construction of the end-point, are considered. A graphical method is presented for the selection of pairs of ranges which result in small systematic titration errors. For equal values of S/C_x² and 1/KC_x, the optimum combinations of ranges are different for precipitation and complexation titrations. The differences are not large for values smaller than about 0.002. For titration curves with a reversed L-shape, the error is calculated when the end-point is constructed by the intersection of the tangent to the second branch of the curve with volume axis; in this case equal ranges result in the same titration error for equal values of S/C_x² and 1/KC_x. The systematic titration error is equal to -S/C_x² when the tangent to the curve is taken at f_a = 3.0.     

Determination of some steroidal bases in non-aqueous media by potentiometric titrations at a small constant current

In this work the volumetric and coulometric titrations of some newly synthesized androstene steroidal compounds with pyridine ring are carried out. The titrations were followed potentiometrically at a small constant current using pairs of identical platinum or glassy carbon electrodes, both in presence of quinhydrone. As the titration reagent, in volumetric titrations served 0.01 mol dm^?3 perchloric acid, and in coulometric titrations hydrogen ions were anodically generated in situ from quinhydrone at the platinum electrode. Sodium perchlorate served as the supporting electrolyte.Amounts of 1.18-5.35 mg of the investigated steroidal compounds were determined with a relative standard deviation less than 1.4% at volumetric and 1.2% at coulometric determinations. A negative influence of the supporting electrolyte on magnitude of the signal change in potentiometric determinations was observed. Glassy carbon electrodes are more advantageous over platinum ones.The achieved results are in good agreement with those of catalytic thermometric titrations.     

Titrimetric applications of multiparametric curve-fitting : Part 1. Potentiometric titrations of weak bases with strong acids at extreme dilutions

A multiparametric curve-fitting procedure is described for locating the equivalence point of a potentiometric titration and is applied to data obtained in titrations of acetate ion with hydrochloric acid over a wide range of concentrations (down to 6.5 · 10^-5M acetate). It does not depend on the existence of a point of inflection on the titration curve, and therefore yields useful results in titrations of this very weak base at concentrations well below that at which the point of maximal slope disappears. Three parameters are involved: the concentration of the base being titrated, the concentration dissociation constant K_a of its conjugate acid in the medium employed, and the apparent activity coefficient y_H⁺ of hydrogen ion in that medium, and all three of these must be evaluated when a new supporting electrolyte is employed. In 3.0 M potassium chloride at 24°, the apparent activity coefficient of hydrogen ion is 1.746₀, and this value permits data obtained in titrations of other or unknown bases in this medium to be interpreted by two-parameter fits. The value of K_a for acetic acid in this medium is 1.313₄ · 10^-5M; by means of these two numerical values routine titrations of acetate in this medium can be interpreted by one-parameter fits. It is possible to locate the equivalence point with an accuracy and a precision that cannot be approached by other techniques and even to obtain useful and reliable results under conditions so unfavorable that other techniques fail completely.     

Enthalpies of ionization for 2,3-diphosphoglyceric acid

A commercial titration calorimeter, modified to measure as little as 2 mcal in 2 mL, was used to perform thermometric titrations on 2,3-diphosphoglyceric acid with both tetraethylammonium hydroxide and sodium hydroxide. The enthalpies of ionization for each of the five ionizable protons on 2,3-diphosphoglyceric acid were derived from calorimetric data to be 0.0±0.3 kcal-mol^?1. Similar titrations with HCl on the penta-anion produced results that are consistent with the values derived from the titrations with base.     

Ti/TiO2 indicator electrodes formed by plasma electrolytic oxidation for potentiometric analysis

Ti/TiO₂ indicator electrodes were prepared by plasma electrolytic oxidation (PEO) method in the tetraborate electrolyte and were used for potentiometric indication of chemical reactions of different types and for analysis of surface and industrial wastewaters on the example of potentiometric determination of alkalinity and chloride. The electrodes formed at current densities of 0.05, 0.1, 0.15 and 0.2 A/cm² are different in composition, surface morphology and electroanalytical properties. The electrodes formed at a current density of 0.05 A/cm² exhibit the highest pH-sensitivity and generate the highest analytical signal at the equivalence point in the acid–base and precipitation titrations. The maximum analytical signal at the equivalence point, exceeding in magnitude the analytical signal, obtained by classical Pt electrode in oxidation–reduction and complexometric titrations generates PEO layers formed at a current density of 0.05 A/cm² and a platinum-modified nanoparticles. The results of the potentiometric titration of the surface and technogenic waters using as indicator Ti/TiO₂ electrodes are comparable with the conventionally used glass electrode (to determine alkalinity) and Ag electrode (to the determine chloride) and the results of visual titration. The advantage of the obtained metal oxide systems is the ability to determine two hydrochemical parameters due to their multifunctionality and opportunity to work with a single electrode. In addition, these sensors offer some analytical characteristics such as sensitivity, good reproducibility, high mechanical stability and a simple preparation procedure.     

High frequency titrations: The mercury(ii)-thiocyanate reaction

Soluble complex-formation of mercury(II) thiocyanate has been studied oscillometrically. The titration of mercury(II) nitrate with thiocyanate gives one inflection corresponding to the formation of Hg(SCN)₂, while in the reverse titration the formation of Hg(SCN)⁺ is also indecated. The method is useful for a rapid determination of very small quantities of mercury or thiocyanate in highly dilute solutions. The titrations can be effected in presence of nitric acid provided its total acidity in the system does not exceed about $\text{1}\text{300}$N. Further Work on the mercury(II) -halide and mercury(II)-cyanide reactions is in progress.     

Determination of Point of Zero Charge of Tunisian Kaolinites by Potentiometric and Mass Titration Methods

This paper deals with determining points of zero charge of natural and Na⁺‐saturated mineral kaolinites using two methods: (1) acid‐base potentiometric titration was employed to obtain the adsorption of H⁺ and OH^? on amphoteric surfaces in solutions of varying ionic strengths in order to determinate graphically the point of zero net proton charge (PZNPC) defined equally as point of zero salt effect (PZSE); (2) mass titration curve at different electrolyte concentrations in order to estimate PZNPCs by interpolation and to compare with those determined by potentiometric titrations. The two methods involved points of zero charge approximately similar for the two kaolinites between 6.5‐7.8, comparable to those reported previously and were in the range expected for these clay minerals. The comparison of potentiometric surface titration curves obtained at 25 °C and those published in the literature reveals significant discrepancies both in the shape and in the pH of PZNPCs values.     

Anionic surfactant selective electrode for the titrimetric determination of anionic surfactant

The construction and characteristic performance of a PVC membrane electrode responsive for sodium dodecylsulfate (SDS) are described in this paper. The electrode based on CTA⁺DS^? ion pair as ionophore in PVC membrane displays a Nernstian slope of ?58.8 ± 0.7 mV/decade in a 1.32 × 10^?6 to 3.75 × 10^?3 mol L^?1 concentration range and a limit of detection of 1.13 × 10^?6 mol L^?1. The electrode can be used for 3 months without showing significant changes in the value of slope or working range. The electrode has been utilized as an end point indicator electrode for potentiometric titration involving Hyamine as titrant. More than 100 titrations were carried out for the evaluation of the electrode parameters: the standard deviations of the equivalent volume and the equivalent potential, the height of the potential jump and the number of faulty titrations. The behavior of the electrode was assessed with regard to their usefulness in routine analysis.     

Bestimmung von Sulfid-, Sulfit- und Thiosulfat-Ionen nebeneinander in Bariumcarbonat und Strontiumcarbonat

In one sample the total “iodine titer” is determined by iodometric titration in acid medium. In a new sample the SO₂ from the sulphite ion is determined after distillation in presence of mercury(II)chloride from hydrochloric acid medium and in a third sample the thiosulphate ion is determined by iodometric titration in presence of cadmium acetate and formaldehyde. The concentration of sulphide ion is calculated from the results of the three titrations as difference. This method can be applied to the determination in magnesium carbonate and calcium carbonate. Standard deviation is ±0.0007% and ±0.0089% for SO₃ ^2? and S₂O₃ ^2?, respectively.     

Thermodynamics of coupled reactions by the amplitudes of chemical relaxation

The amplitudes of the relaxation curves, as obtained by the Temperature-jump method have been used to measure simultaneously equilibrium constant and enthalpy for the reaction of complex formation of Ni²⁺ ion by 2,6-dihydroxobenzoic acid in the presence of a buffer. The experiments have been performed by changing the concentration of metal ion at constant ligand concentration andpH as in a complexometric titration. The points of such ‘dynamic titrations’ have been analysed by means of the concept of ‘normal reactions’ which enabled us to transform a set of coupled individual steps into a set of kinetically independent reactions. The potentialities of the dynamic titrations are discussed.     

2-Hydroxy-naphth-1-aldehyde phenyl-thiosemicarbazone: effective thiourea-based sensor for acetate anion

A novel urea-based sensor displaying selective recognition for AcO^? had been designed and synthesized. Experiments showed that sensor 1 can selectively recognize acetate in DMSO. The evaluation of the sensor’s interaction with a variety of structurally different anions was performed by UV–vis titration experiments in DMSO. In addition, the nature of interaction between sensor 1 and AcO^? was investigated by ¹H NMR titrations.     

Solution Equilibria. A Unified Mathematical Treatment of Experimental Polarographic and Potentiometric Data from Acid?Base and Ligand Titrations. A Polarographic and Ion Selective Electrode Study of CdII?(N‐(2‐hydroxyethyl)iminodiacetic acid)?OH System

It has been demonstrated that potentiometric and polarographic data coming from either acid? base or ligand titrations can be evaluated by the same set of equations and mathematical procedures involving mass‐balance equations written for any metal? ligand model, including polynuclear species. It is shown that the concept of the complex formation curves, used previously in modeling and refinement of stability constants in acid‐base titration, is of general nature and can be successfully used in polarographic and potentiometric experiments conducted as a function of pH or an excess of a ligand. It appears that the linear relationship ΔE vs. log [M], typical for potentiometric studies with ISE, holds also in the case of the study of kinetically mixed metal‐ligand system studied by polarography when the corrected shift in the polarographic signal is used. The relationship ΔE vs. log [M] applies equally to the acid‐base and ligand titration for both experimental techniques employed (potentiometry and polarography). The significance of the corrected shift is discussed and its meaning in the study of kinetically fast or slow metal? ligand systems is elaborated. Advantages of the acid‐base titration over the ligand titration are discussed. The generalized mathematical data treatment was successfully employed in the study of the Cd^II? (N‐(2‐hydroxyethyl)iminodiacetic acid) system. Results obtained from both analytical techniques (potentiometry with the use of an ion selective electrode, and two polarographic techniques) and analytical procedures (acid? base and ligand titrations) compare well with each other and with the literature data (the formation and stability constants of ML and ML₂). In addition, a new complex M(HL) was identified and its stability constant is reported.     

Adsorption from mixtures containing mono- and bivalent cations on insoluble oxides and a revision of the interpretation of points of zero charge obtained by titration

Acid—base potentiometric titrations of haematite (α-Fe₂O₃) suspensions in mixtures of the non-specifically adsorbing electrolyte KNO₃ and the nitrates of the specifically adsorbing ions Ca²⁺, Cd²⁺ and Pb²⁺ show that the cross-over point of the titration curves, plotted as σ₀(pH), can be interpreted as the point of zero charge (pzc) only if there is no specific adsorption or if the amount of specifically adsorbed cations is so small that all of it is quantitatively adsorbed. This finding implies that the usual procedure for obtaining the pzc from cross-over points of titration curves must be reconsidered in the case of specific adsorption. In reality an Esin—Markov coefficient is measured, the relation of which to the surface charge requires further thermodynamic analysis.