Thermometric titration in investigation of the formation of polyanions of molybdenum(VI), tungsten(VI), vanadium(V), and chromium (VI)-I: comparison of thermometric and potentiometric titration curves

A new twin-cell thermometric titrator has been devised and used for thermometric titration of solutions of sodium molybdate, sodium tungstate, sodium orthovanadate, ammonium metavanadate, and potassium chromate with perchloric acid. The thermometric titration curves were compared with corresponding pH-titration curves for elucidation of the reactions occurring in the titrations. Thermometric titrimetric methods have been developed for the determination of tungsten, vanadium and chromium.     

Present state and future development of instrumental techniques for solution thermochemical (thermometric) analysis

A review of instruments for thermochemical (thermometric) solution analysis is given, including new types of isoperibol reaction of bomb calorimeters, the design of which can influence the future development of thermochemical measuring techniques. The new type of Dithermanal (Vaskut-EMG, Hungary, and Herrmann- Morris, France) controls the individual steps of the thermochemical analysis, adding memory and computing capabilities. Similar programming units with microprocessors for bomb and/or reaction calorimetry have been developed by Parr Comp. and Leco Comp. (USA). The latest modification of the Technicon flow analyzer permits on-line analysis of solid samples. For thermochemical titrations, the Sanda titrator (USA) and Vaskut automatic titrator (Hungary) are available. In the USA, the Tronac isothermal or isoperibol calorimeters are widely used. At the Technical University of Brno, ?SSR, smaller table instruments with a water-bath are applied for different modes of solution thermochemical analysis, and also for the reactions of solid samples in liquids. For the measurement of very small temperature differences, PTC thermistors are used. The possibilities of the future development of measuring techniques are outlined.     

Thermometric titration of some molybdates,molybdic acid,and molybdenum trioxide

A thermometric titrator equipped with differential thermistor is used for the titration of molybdenum in sodium molybdate, potassium molybdate, magnesium molybdate, tetramethylammonium molybdate, and tetraethylammonium molybdate, based on their reactions with hydrochloric acid, and in ammonium paramolybdate, molybdic acid, and molybdenum trioxide, based on their reactions with sodium hydroxide. Orthomolybdates and ammonium paramolybdate were determined in the 0.5–0.005 M range; sufficient solid molybdic acid or molybdenum trioxide was taken to give a final 0.01–0.5 M solution in 20 ml of water. The method is simple and very quick. The standard deviation varies from 0.5 to 1.5% depending on the amount of sample taken.     

Oxidability Determination in Waste Waters Using an Automatic Titrator Based on a Multicommutated Unsegmented Flow System

Abstract

The automatic titrator based on a multicommutated unsegmented flow system was applied to redox titrations and used for oxidability determination in waters analysis. This automatic titrator allows the attainment of complete titration curves, being the determination of titrand concentration performed without requiring any prior calibration. After sample treatment (oxidation step), the oxidability determination in waste water samples was accomplished by the automatic flow titrator (titration step). Repeated determinations of standard solutions gave a 3.5% RSD (n=10, 0.010M) for repeatability and a 3.2% RSD (n=2, 0.057M) for reproducibility. Samples results (n=9) were in good agreement (t-test) with those obtained with a reference procedure.     

Thermometric titrations at elevated temperatures

The oxidizing power of hexacyanoferrate(III) in alkaline conditions is wellknown. Unfortunately many if its oxidation reactions are too slow at room temperatures for direct titrimetric procedures. A method has been developed for the determination of millimolar amounts of selenium(IV), arsenic(III), antimony(III), chromium(III), and thallium(I) using thermometric titrimetry at approximately 330 K. The reproducibility and accuracy of the method are approximately 1%.     

Mechanisiertes thermometrisches Analysenverfahren zur Bestimmung von Substanzen in weiten Konzentrationsbereichen

A procedure for mechanised thermometric analysis is described which can be used for the continuous analysis of sample streams as well as for the determination of components in individual samples. In contrast to thermometric methods of analysis previously used, this new procedure is particularly applicable for substances present in medium to high concentrations, and is therefore suitable for many industrial purposes. The analytical exploitation of enthalpy changes as for example with neutralisation, redox and precipitation reactions as well as with dilution, opens wide application possibilities. The precision of the results is generally very good.     

一种新型自动数字滴定管的研制

本文报道一种新型自动数字滴定管，采用马利奥特恒流器和石英数字计时器设计而成，液流无脉动、无滞后，滴定剂用量（或滴定度）用时间计量和数字显示，避免了使用容量滴定管产生的问题和困难，这种自动数字滴定管电路简单，造价低廉、操作简便，可简便地与计算机连接以实现自动化，实际应用结果令人满意。     

Thermometric studies on the Fe(III)-EDTA chelate

A DeltaH of -11.5 +/- 0.5 kJ/mole has been determined for the formation of the Fe(III)-EDTA chelate at 25.0 degrees and mu = 0.1(= [HClO(4)] + [NaClO(4)]) by a direct thermometric titration procedure. The entropy change, DeltaS, has been calculated to be 440 J.mole(-1) .deg(-1) by combining the result of the heat measurements with the free energy change obtained from the stability constant previously determined. A relationship between the DeltaS values and the standard partial molal entropies of the tervalent metal ions is discussed. In addition, conditions for the thermometric titration of Fe(III) with NA(4)EDTA at room temperature have been investigated. Iron(III) can be determined in the presence of fairly large amounts of phosphate, Cr(III), Mn(II) and Al(III).     

Rapid and accurate titrations with a convenient and compact automatic derivative spectrophotometric titrator

A convenient and compact automatic derivative spectrophotometric titrator is described which is suitable for automatically performing a wide variety of the well known color indicator titrations without any procedure modifications and usually with few, if any, pretitration considerations and instrument adjustments The results for many acid-base and oxidation-reduction titrations are presented to illustrate the general applicability and important characteristics of the instrument     

Elucidation of coordination polymer stoichiometry via thermometric titrimetry: Metal complexes of trithiocyanuric acid

An attempt has been made to elucidate the stoichiometry of the coordination polymers formed by trithiocyanuric acid with some metals in both dimethyl formamide and aqueous solution. It is possible, using the technique of thermometric titrimetry, to assign stoichiometries to a number of these complexes. In some cases, however, the solid phases that separate are non-stoichiometric. Comparison is made with the stoichiometries of metal complexes of the related ligands, cyanuric acid and melamine as determined via thermometric titrimetry. This technique is shown to be successful and rapid, in contrast with the conventional procedure.     

Photometric determination of trace selenium in aqueous media

A new procedure is developed for the photometric determination of trace selenium in aqueous solutions. The selection of 2-(p-nitrophenyl)-3,5-diphenyltetrazolium chloride as a reagent for selenium is justified. The proposed sample preparation procedure involves gas extraction of selenium as hydrogen selenide followed by its liquid-adsorption extraction from the gas phase to an aqueous reagent solution with the formation of a water-insoluble formazan. Formazan formed upon the absorption of hydrogen selenide is extracted with isoamyl alcohol. The concentration of selenium is determined from the absorbance of the formazan extract in the isoamyl alcohol. The procedure allows the determination of 10–120 μg/L selenium.     

Spectrophotometric determination of selenium with 6-amino-1-naphthol-3-sulphonic acid (J-acid) and its application in trace analysis

A selective procedure for spectrophotometric determination of selenium with 6-amino-1-naphthol-3-sulphonic acid (J-acid) is described. In acidic conditions selenium forms a yellow complex with J-acid which has an absorption maximum at 392 nm. The molar absorptivity is 1.48 x 10(4) 1 mol(-1)cm(-1). Beer's law is obeyed for selenium in the range of 0.08-0.8 mg/1. The method has been applied to the determination of trace amounts of selenium in water, polluted water, plant material and steel plant dust. The proposed method is sensitive, rapid, simple and accurate.     

Hydride generation atomic absorption spectrometry with insitu graphite tube trapping for the determination of Se (IV) and Se (VI) in baltic sea water samples

This paper reports the results of an optimisation study for a procedure to determine the total selenium and its inorganic species, Se(IV) and Se(VI) using atomic absorption spectrometry combined with hydride generation and in-situ trapping of the analyte on the inner walls of the graphite tube. With the use of the proposed modification, a detection limit (3σ) of 0.018 ng/ml is achieved. This paper presents exemplary results, according to the proposed procedure, for selenium determination in samples of marine water. The concentrations of selenium in the samples ranged from <0.02 ng/ml to 0.16ng/ml of Se(IV) and from <0.02 ng/ml to 0.10 ng/ml of Se(VI).     

Selenium speciation in animal tissues after enzymatic digestion by high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry

A procedure is described for the enzymatic digestion of tuna and mussel samples that allows the determination of selenium species by high-performance liquid chromatography in conjunction with inductively coupled plasma mass spectrometry. The species were extracted by two-step enzymatic hydrolysis with a non-specific protease (subtilisin). The selenium species were separated on a Spherisorb 5 ODS/AMINO column using two different chromatographic conditions, namely phosphate buffers at pH 2.8 and pH 6.0 as mobile phases. The method determines organic (trimethylselenonium, selenocystine, selenomethionine and selenoethionine) and inorganic selenium species (selenite and selenate), but only organic selenium species were found in the samples. The sum of identified selenium species in the sample was about 30% of the total selenium present in the enzymatic extract despite the fact that recoveries of total hydrolysed selenium were 93-102%. Trimethylselenonium ion and selenomethionine were found in both tuna and mussel samples and an unknown selenium species was also found in tuna samples.     

Dosage par spectrophotométrie d'absorption atomique sans flamme de traces de sélénium après extraction à l'aide de 4-chloro-1,2-diaminobenz̀ application aux milieux biologiques

The determination of traces of selenium after extraction with 4-chloro-1,2-diaminobenzene by graphite-furnace atomic absorption spectrometry, Application, to biological samples.A new method for the determination of very small amounts of selenium by flameless atomic absorption spectrometry is proposed. The procedure was checked with aqueous solutions of selenium and applied to mineralized biological fluids (red cells and plasma). Selenium(IV) is quantitatively extracted with toluene after reaction with 4-chloro-l,2-diaminobenzene. The sample detection limit for selenium is 10 ng ml^-1. Precision and reproducibility are excellent.     

Preconcentration and separation of inorganic selenium on Dowex 1X8 prior to hydride generation-atomic absorption spectrometry

Exchange reactions between inorganic selenium species and chloride were studied on Dowex 1X8. The concentration exchange constants were determined with the batch technique at room temperature and used to predict the chromatographic enrichment and separation of tetra- and hexavalent selenium. A procedure for the determination of total selenium after digestion with permanganate and anion exchange preconcentration was also developed. The enrichment techniques were applied to the determination of Se(IV) and total dissolved selenium in drinking water and fresh water using flow injection hydride generation-atomic absorption spectrometry (HG-AAS). Results agreed with those obtained in a HG-AAS system where selenium was preconcentrated as hydrogen selenide in a trap at liquid nitrogen temperature.     

Determination of Selenium in Foodstuffs by Cathodic Stripping Voltammetry at a Mercury–Graphite Electrode

A universal procedure was developed for the voltammetric determination of total selenium in various foodstuffs. The procedure involves the mineralization of a test sample with magnesium nitrate followed by the reduction of selenium(VI) to selenium(IV) in 6 M HCl and the determination of selenium by cathodic square-wave voltammetry at a mercury–graphite electrode in an HCl solution in the presence of copper and mercury ions.     

Quantitative HPTLC determination of selenium

The present determination of selenium in biological matrices by HPTLC with in situ fluorimetric detection is an accurate alternative method, comparable to other established methods such as photometry, polarography, neutron activation, or X-ray fluorescence analysis, gas chromatography, and atomic absorption spectrometry. The excellent sensitivity of this procedure is proved by the detection limit of 250 fg of selenium per spot (using purified 2,3,1-naphthoselenodiazole). The oxidation of organic matrices, applying a novel digestion procedure, may be carried out with little instrumental expenditure. Sample preparation steps, such as the oxidation of selenium to Se (VI) and subsequent reduction to Se (IV) do not lead to significant random or systematic errors, nor does the digestion step, if an optimized procedure is used. A recovery rate of 103% and nearly parallel calibration curves for digested selenocysteine standards compared with spiked human serum samples demonstrate the accurate quantitative preparation of a biological matrix. Any interfering metal ions can be masked by addition of chelate-forming reagents.     

Coprecipitative Preconcentration and Differential Pulse Cathodic Stripping Voltammetric Determination of Selenium (IV)

Abstract

A DPCSV procedure for the determination of selenium (IV) with a prior preconcentrative coprecipitation on iron (III) hydroxide has been developed. The experimental conditions for coprecipitation of selenium (IV) onto iron (III) hydroxide, viz. pH, iron (III) concentration, volume of aqueous phase and selenium concentration, were optimized. The coprecipitated selenium (IV) is dissolved in 10 ml of 0.1 M HCl and analysed using DPCSV in the presence of copper (II). Selenium concentrations as low as 10–100 ng present in 500 ml of the aqueous phase could be determined. The method is precise and has been applied to the analysis of sea water and reference material samples.     

一种新型气压式滴定仪的研制

介绍一种新型气压式滴定仪的结构、性能、特点及使用方法。该仪器能迅速、准确地加液调零,使用方便,克服了旧式滴定管漏液、取液时易玷污、加液调零较麻烦等缺点,在适当的情况下还可以作为移液管使用。