The effect of morphological changes on the coprecipitation of strontium by calcium phosphate

The coprecipitation of strontium by a calcium phosphate phase formed at an elevated pH 10.8 was investigated. The first phase obtained under these conditions in the amorphous calcium phosphate (ACP) which is transformed into crystalline hydroxyapatite (HA) after the induction period. Is has been shown that this transformation together with morphological changes of the precipitated solid phase, influences the amount of the sorbed strontium significantly. The possible consequences of this finding on practical application of coprecipitation of strontium by calcium phosphate have been discussed.     

Excess and partial excess molar volumes of mixing of N,N-dibutyl-2-ethylhexamide with dodecanol

Excess and excess partial molar volumes of mixing of the system N,N-dibutyl-2-ethylhexylamide (DBEHA) + dodecanol (DDA) were determined at 25, 35, 45, 55 and 65°C. The excess molar volumes exhibit a maxima at each temperature at approximatelyx _DBEHA = 0.3 and a minima close tox _DBEHA = 0.9. The values of the excess volumes in general increase with the temperature. The partial excess molar volumes are calculated from the smoothed data and the results are discussed in the light of postulated amide-alcohol interactions.     

Analytische Aspekte der Oxydation organischer Stickstoffverbindungen mit Chromsäure. XXIII

Zusammenfassung Die früher beschriebene Halbmikromethode zur Bestimmung von Isonitrosogruppen in organischen Verbindungen wurde in den Mikromaßstab übergeführt. Sie beruht auf der Reaktion der Substanz mit Eisen(III)-sulfat in verd. Schwefelsäure. Dabei wird der Oximstickstoff als Distickstoffoxid frei, das mit Kupfer zu elementarem Stickstoff reduziert und im Mikroazotometer gemessen wird. Für die Berechnung des Oximstickstoffgehaltes aus den abgelesenen Gasvolumina wurden Werte für die konstante und proportionale Volumenkorrektur mit Hilfe der Methode der Regressionsgeraden experimentell festgestellt. Beide Werte sind den bei der N-N-Gruppenbestimmung benützten Volumenkorrekturen fast gleich. Die Bestimmung von Oximgruppen ist durch die Anwesenheit von Nitro- oder Aminogruppen nicht gestört. Diese Gruppen können aus derselben Einwaage durch nachfolgende Oxydation mit Chromsäure bestimmt werden.

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Analytical aspects of the oxidation of organic nitrogen compounds with chromic acid. XXIII

Summary The semimicro method previously described for the determination of isonitroso groups in organic compounds has been converted to the microscale. It is based on the reaction of the material with iron(III)-sulfate in dilute sulfuric acid. The oxime nitrogen is thus liberated as dinitrogen oxide, which is reduced to elementary nitrogen by copper and measured in the mieroazotometer. To calculate the oxime nitrogen content from the read-off gas volume, values for the constant and proportional volume correction with the aid of the regression lines were established experimentally. Both values are almost equal in the case of the determination of the volume corrections employed in the determination of the N-N-groups. The presence of nitro-or amino groups does not interfere with the determination of oxime groups. These groups may be determined from the same sample by subsequent oxidation with chromic acid.

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XXII. Mitteilung s.¹.     

Flow injection analysis : Part IX. A New Approach to Continuous Flow Titrations

Studies of dispersion patterns in nonsegmented streams, flowing through narrow open tubes, show that it is possible to obtain highly reproducible concentration gradients within a sample zone injected into the moving stream. By varying the geometry of the flow path, low, medium and high dispersion patterns can be achieved; the high dispersion pattern forms the basis for a new approach to continuous flow titrimetry. In this type of titration, discrete samples are passed through a gradient device and are then mixed with a continuously flowing stream of titrant of fixed concentration. The new technique has been tested for potentiometric as well as spectrophotometric end-point indication. A simple one-channel system allows titrations to be performed automatically in less than 1 min.     

Rapid determination of protein in plant material by flow injection spectrophotometry with trinitrobenzenesulfonic acid

The rapid determination of protein in plant material based on spectrophotometric determination of amino acids in protein hydrolysates with trinitrobenzenesulfonic acid has been adapted to flow injection analysis. With the manifold described, a routine sampling rate of 120 samples/h is possible, though this, as well as sensitivity, can easily be varied. The method was calibrated against the Kjeldahl method and a good correlation was obtained between the two methods over a wide range of protein values for beans.     

A set of four soil reference materials with certified values of total element contents and their extractable fractions

A set of certified reference materials of four natural soils denoted as CRM 7001-4 was prepared. They consist of light sandy soils with normal and elevated, silty clay loam with normal, and loam with elevated element levels. Certified and/or information values were established for the total contents of the elements As, Ba, Be, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, V, Zn, and their fractions, extractable with aqua regia, and boiling and cold 2 mol L^–1 nitric acid, from results of a 28 laboratory intercomparison using various methods of atomic absorption spectrometry, optical emission spectrometry, mass spectrometry, electrochemical methods, spectrophotometry, instrumental neutron activation analysis, and X-ray fluorescence.     

Gold(III) complexes with imidazole,benzoxazole, purine and pyrimidine derivatives

Summary The synthesis and characterization of Au^III complexes with several heterocyclic ligands are reported. The compounds have general formula [AuX₃(L)], where L =N-methylimidazole (N-MeIz),N-ethylimidazole (N-EtIz),N-propylimidazole (N-PrIz), benzoxazole (BO), 2-methylbenzoxazole (2-MeBO), 2,5-dimethylbenzoxazole (2,5-diMeBO), 2-amino-pyrimidine (2-APm), 4(6) -hydroxy-pyrimidine [4(6)-hydrPm] or hypoxanthine (Hypox) and X = Cl or Br. Elemental analysis, conductivity measurements and spectral studies were used for the characterization of the complexes. A square-planar geometry withN-bonded heterocyclic ligands is suggested.     

Study of the drying zirconia gel-precipitates using thermal analysis

Thermoanalytical techniques (TG, DTG, DTA and EGA) can be helpful in studying gel compositions and relating the chemical history and the role of the precipitant to the chemical properties of gels. The objective of our work was to determine the influence of the initial conditions in the reaction mixture on the product characteristics. Zirconia gels were prepared by the gelprecipitation method by the hydrolysis of zirconium tetrachloride dissolved in methanol. The substitution of water by methanol was chosen in order to obtain a reaction medium in which better control of the hydrolysis and condensation reactions of the zirconium precursor were achieved and thus also better control of the final properties of the dried zirconia gel-precipitates could be obtained. The nature of the hydrated zirconia gels obtained during the gelation process is strongly influenced by the conditions of the reaction mixture, e.g. concentration of the zirconium precursor, the mixing rate and particularly by the amount of water added. To distinguish between various types of water in the gel-precipitates, the furnace atmosphere and the partial water pressure were altered appropriately. It was shown that initial zirconium to water molar ratio has a significant effect on the properties of the final products. It was assumed that, according to the preparation conditions, three different types of water are present in the formed zirconia gel-precipitates. Modification of the dehydration processes of zirconia gel-precipitates enables control of the final microstructural and surface properties of the dried gels which are suitable for further catalysts support as well as mixed oxide preparation.     

Polarographic determination of stability constants and thermodynamic parameters of lead(II) propanoate and 2-hydroxypropanoate complexes with a computer-controlled system

A computer-controlled electrometric system is described. It is used for d.c. polarographic determinations of the stability constants of lead(II) propanoate and 2-hydroxypropanoate complexes at four temperatures. From the values of the monoligand complex stability constants obtained at different temperatures, standard thermodynamic functions (ΔH_j and ΔS_j) for the first and second steps of complex formation were obtained. Closed-loop interaction between the minicomputer and electrometric instrument was achieved through computer control of the potentiostat, drop-life timer, burette and valve for nitrogen purging. Computer programs are outlined for numerical and statistical evaluation of the experimental data giving E_{$\text{1}\text{2}$}i_d and slope of logarithmic presentation of polarograms, F_o functions and cumulative stability constants, β_j as well as for calculation of the standard thermodynamic functions.     

The stability constant ratios of tri-N-octyl amine hydrochloride and bisulphate

The equilibria between the solution of TOA in toluene and mixtures of sulphuric and hydrochloric acid been studied. They were characterized by ratios of stability constants of amine salts formed in the organic phase.