Optimization of the Micro-Scale Determination of Arsenates by Direct Potentiometric Titration with Silver Ions and its Application to the Determination of Arsenic in-Organic Compounds

Abstract

A micro-scale argentimetric method for the determination of orthoarsenates by potentiometric detection of the end-point has been developed. The optimal results were obtained when this titration was carried out in water-methanol medium, buffered at pH 7.50. This method minimizes the error of old methods arising from the small coprecipitation of silver oxide near the equivalence point and the data obtained are characterized by good accuracy and reproducibility. The procedure to perform the titration with an automatic apparatus is described as well as the optimum concentration range and titration rate. The method was then applied to the determination of arsenic in organic compounds after mineralization in the Schöniger flask using a quartz spiral.     

Coulometric Titration of Thiocyanate,Mercaptoacetic Acid,and β-Mercaptopropionic Acid with Electrogenerated Hypobromite

Abstract

Several sulfur containing ligands have been determined by coulometric titration using biamperometric end point detection. Satisfactory results were obtained for the direct determination of thiocyanate, mercaptoacetic acid and β-mercaptopropionic acid. Silver has been determined by an indirect method involving the determination of excess precipitant.     

Titration of Anionic Surfactants Using a New Potentiometric Sensor

Abstract

An anionic surfactant ion selective electrode has been developed by coating the Ru?i?ka Selectrode with plasticised polyvinyl chloride containing hyaminedodecylsulfate active substance. The electrode responds to dodecylsulfate, in the range 10^?2 ? 10^?2 mol dm^?3 and has been used for potentiometric titration of micromolar amounts of dodecylsulfate with an accuracy of 0.3%. The influence of several organic and inorganic anions has been investigated.     

Direct Photochemical Titration of a Fluorescent Compound

Abstract

The direct titration of quinine with ultraviolet photons is reported; previous titrations have used an intermediate photogenerator. A single mercury vapor arc was used to both photolyze the sample and to induce fluorescence; the latter is used to follow the course of the titration. Linear calibration plots were obtained over the range of 0.13 to 3.33 ppm of quinine with relative standard deviations as low as 1.6%.     

Towards a Standard Method for the Measurement of Organic Carbon in Sediments

Abstract

The precisions achieved by two different methods for analysis of organic carbon in soils and sediments were determined and compared. The first method is a rapid dichromate oxidation technique (Walkley-Black) that has long been a standard in soil chemistry. The second is an automated coulometric titration method for which commercial instrumentation is available. The latter method shows relative standard deviations that are six to twenty times smaller than the dichromate oxidation technique. Development of a standardized sediment with a low level of organic carbon is recommended in order to facilitate the evaluation of the precision and accuracy of organic carbon measurement techniques.     

Potentiometric Titration of Weak Acids

Abstract

A desk-calculator program has been developed for determination of the equivalence point when a weak acid is titrated with a strong base. The stability constant (K^H _HA) of the acid can be computed simultaneously. When data from a potentiometric titration of boric acid with sodium hydroxide have been processed with the program the equivalence point has been determined with an accuracy of 0.3–0.4 per cent. The computed value of the stability constant of boric acid (log K^H _HA = 9.11) is in good agreement with the values given in literature.     

The Potentiometric Titration of Soaps Using a Liquid Membrane Electrode

Abstract

A liquid membrane soap or surfactant sensitive electrode capable of working throughout the pH range 1–13 has been developed. The active substance of the electrode is the ion-association complex of dodecylbenzene sulphonate with bisdimethylglyoxime-o-phenanthroline-cobaltate(III). The electrode enables soap or surfactant titration depending on the pH.     

Self-assembly snapshots of a 2 × 2 copper(I) grid

Self-assembled 2 × 2 grids have been characterised as high-fidelity species produced when the correct stoichiometric ratios are met, but rarely are the individual steps leading to and from their formation characterised. Here, we present such a study using equilibrium-restricted factor analysis to model a set of UV–vis spectra starting from a bis-bidentate ligand to the assembly of a 2 × 2 grid complex upon titration with 1 equiv. of [Cu(MeCN)₄](PF₆) and to disassembly upon further titration. Intermediate species [CuL₂]⁺, [Cu₂L₃]²⁺, [Cu₃L₂]³⁺ and [Cu₂L]²⁺ are evidenced along the assembly and disassembly pathways. Complementary ¹H NMR titrations are consistent with the rich set of complexes and equilibria involved. Given the nature of the assembly process, the assembly is entropy driven and likely enthalpy driven as well. The disassembly process is both enthalpy and entropy driven according to the standard free energy values derived from the modelling of the spectrophotometric titration data.     

The Titrametric Determination of Rhenium

Abstract

A spectrophotometric titration for the determination of rhenium was developed using tin(II) as the titrant. Samples containing approximately 1 × 10^?2 meq/ml were titrated with errors of approximately four percent. Titration of rhenium was investigated in the presence of glucose, ethanol, and oxalate. No significant induced reactions were shown to occur.     

Titration of Anionic Surfactants in a Mixture,Using a Surfactant Exthactive Electrode

Abstract

Mixtures of sodium octylsulfate with sodium dodecyl-benzenesulfonate or sodium di-2-ethylhexglsulfosuccinate (Aerosol OT) were determined potentiometrically. The titration curve permits the simultaneous determination of both components with en accuracy of 1.0%.     

Coulometric Titration of Free Cyanide with Electrogenerated Hypobromite

Abstract

A rapid and sensitive method is described for the direct determination of cyanide by coulometric titration with electrogenerated hypobromite. A biamperometric end point was utilized. From 0.498 – 9.980 ueq of cyanide were analyzed with an average error of 0.36% and an average standard deviation of 0.045.     

2-氯-4-氟苯甲酸与5，5'-二甲基-2，2'-联吡啶镧系配合物的晶体结构、光谱和热行为

合成并表征了2个双核配合物[Pr （2-Cl-4-FBA）₃（5,5''-DM-2,2''-bipy）]₂（1）和[Dy （2-Cl-4-FBA）₃（5,5''-DM-2,2''-bipy）]₂·2（2-Cl-4-FHBA）（2）,其中2-Cl-4-FHBA=2-氯-4-氟苯甲酸,5,5''-DM-2,2''-bipy=5,5''-二甲基-2,2''-联吡啶。配合物1以八配位的Pr³⁺为中心,其周围的配位环境为扭曲的三角十二面体。配合物2的结构是独特的,它包含2个自由的2-氯-4-氟苯甲酸分子,并以九配位的Dy³⁺为中心与周围的氮、氧原子形成扭曲的三棱镜几何构型。这2个配合物均结晶于三斜晶系P1空间群,并通过氢键相互作用和π-π堆积作用形成了一维和二维超分子结构。研究了配合物的热分解过程,结果表明配合物1和2分别分为4步和5步进行分解。同时对配合物的三维红外堆积图进行了研究,结果表明,整个热分解过程中释放出的主要气态产物是水、二氧化碳和有机小分子碎片。配合物2的荧光性质研究表明,它可以发射出Dy³⁺的特征跃迁对应的荧光。     

MgO－B2O3－MgCl2－H2O体系与盐酸滴定反应的研究

ＭｇＯ－Ｂ２Ｏ３－ＭｇＣｌ２－Ｈ２Ｏ是含硼盐湖日晒浓缩盐卤的典型体系，它与盐酸反应生成硼酸，是从天然浓缩盐卤中制取硼酸的工艺基础，以量热滴定法和ＰＨ滴定法研究该反应，结果表明，析出硼酸的反应分两步进行；合成盐卤中硼酸盐可用ＭｇＢ２ｎＯ３Ｎ＋１（ｎ＝１，２，３）综合统计形式来表示；天然浓缩盐卤中硼酸盐可以用四硼酸镁的统计形式进行表示。     

Dosage Simultane Des Traces D′eau Et C′oxygexe Dans Les Solvants Crganiqufs

Abstract

The method involves gas-liquid chromatographtc detenninatlons of samples picked up from the liquid phase of an organometalllc solution and from the gas phase above it; the first sample is hydrolyzed before analysis. Comparfng the results before and after introduction of a known amount of a solvent to be analyzed give simultaneous determination of owgen and water present in this solvent of contents less than one part per million.     

Determination of ß-Diketones by Oscillometric Titration

Abstract

An oscillometric titration technique has been applied to the determination of ß-diketones. Typical accuracies of about ± 1.5% were obtained for the compounds studied. The technique is rapid and simple, and should be suitable to the serial analyses of many compounds of pharmaceutical interest.     

Polyelectrolyte titration using fluorescent indicator. I. Direct titration of anionic and cationic polyelectrolytes with 10−4N standard solutions

The polyelectrolyte titration, which was originally called colloid titration, is based on the stoichiometric reaction between positively charged colloidal particles and negatively charged ones. In the conventional method, the metachromatic color change of the indicator, toluidine blue, from blue to red-purple has been applied for the determination of the end point in the titration. 2.5 × 10^?3N potassium polyvinylsulfonate (KPVS) is usually used as the standard titrant. In this work, fluorescent indicators such as 6-(p-toluidino)-2-naphthalene sulfonate (TNS), acridine orange, etc., have been introduced. The fluorescence intensity was measured using the spectrophotometer equipped with magnetic stirrer and connected with a vinyl tube attached to the hand piston burette. For example, TNS is practically nonfluorescent, but it exhibits strong fluorescence when it is bound to a cationic polyelectrolyte (CP). The fluorescence of the TNS–CP complex is diminished by titration with KPVS standard solution since TNS is liberated from the complex by substitution with KPVS. After the equivalent point, the fluorescence intensity becomes constant and the end point can thus be detected by that point. It has been elucidated that the very dilute standard solution like 1 × 10^?4N can be used because the sensitivity of fluorescence detection is extremely high. © 1993 John Wiley & Sons, Inc.     

Conductometric Titration of Chlorhexidine and Proguanil

Abstract

Conductometric titrations of chlorhexidine and proguanil are reported. The procedure is based on the copper-bi-guanide reaction which gives a pink solid. Studies at several pH values, and presence of NH₃ and ethanol are carried out. 3 ml of 0.2 M NH3, 9ml of 0.01 M NaOH diluted to 60 mL with 15% ethanol are added to 5ml of biguenide aqueous solution and titrated awith cooper acetate. Concentrations of Chlorhexidine in 5.9x10^?5 - 3.4x10^?4 M range are determined. Fareignspecies presence is studied too.

Biguanides are found in several pharmaceutical formulations and industrial samples.

Estimetion of chlorhexidine and proguanil salts with the standard method lacks selectivity since it is based on perchloric acid titration in acetic acid medium¹. Some recent papers about determination of chlorhexidine and proguanil have been publisghed: potentiometric titration of chlorhexidine² polarographic determinetion of praguanil and chlorhexidine^3,4 spectrophotometric assay of chlorhexidine in contact lens solutions⁵ and suppositories⁶, HPLC of proguanil in serum sam-ples⁷ and chlorhexidine in several samples ^8,9,10,10,11 or G C ^12,13 and mass fragmentography^14,15.     

The Stability of the Copper(II)-Eriochrome Red B Complex and the Compleximetric Titration of Copper(II) Ion

Abstract

Values of the conditional stability constant of the copper(II)-Eriochrome Red B complex in aqueous solutions of pH 3–6 have been determined employing a cupric ion electrode. When the ionic strength of the solution is 0.01, the value of the second acidity constant (pk₂) of Eriochrome Red B is 6.28 and the logarithm of the stability constant of the copper complex, log k_CuHI, about 8.2. The complex can be used as an indicator in the ocapleximetric titration of cupric ion with EDTA at pH values from 4 to 8.     

Synthesis of a tetrazine-based catecholamide derivative and its evaluation as a chelating agent for removal of Cd(II), Co(II), and Cu(II)

The synthesis and structural characterization of a tetrazine-based catecholamide (CAM) ligand, N,N′-bis(N″-(aminoethyl)-2,3-bis(hydroxy)benzamide)-1,2,4,5-tetrazine-3,6-diamine (5), were investigated. All compounds were characterized by ¹H NMR spectroscopy, ¹³C NMR spectroscopy, and FTIR spectroscopy. The protonation equilibria of 5 and complexation capacities (log β_pqr) of Cd²⁺, Co²⁺, and Cu²⁺ complexes of 5 were evaluated through potentiometric titration and spectrophotometric titration, respectively. Species independent pM value (=?log [M]_free) was used to compare metal affinities with the final sequence Cu²⁺ > Cd²⁺ > Co²⁺. Results show that 5 has potential for heavy metal removal.