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.     

Determination of heptacaine hydrochloride in solution using nuclear analytical methods

The applicability of two nuclear analytical methods for the determination of hepatacaine hydrochloride in solution was studied, i. e. radionuclide X-ray fluorescence analysis and radiometric titrations based on precipitate formations. Methods used were evaluated on the basis of obtained sensitivity values.     

Corrosion of Cu-xZn alloys in slightly alkaline chloride solutions studied by stripping voltammetry and microanalysis

The mechanism of corrosion of Cu-xZn alloys (x = 10-40 wt %) in slightly alkaline chloride solutions was investigated by analysing solid reaction products by energy dispersive X-ray analysis (EDS) and dissolved reaction products by differential anodic pulse stripping (DAPS) voltammetry. The corrosion process was studied under open circuit and under potentiostatic conditions at selected potentials. Pure metals were studied comparatively so that an interacting effect of particular metal components in the alloy could be determined. All four Cu-xZn alloys show an improved behaviour compared to pure metals. Under open-circuit condition both components dissolve simultaneously in the solution. With increasing immersion time the preferential, dissolution of zinc in the solution becomes pronounced. It is the highest for Cu-10Zn and the lowest for Cu-30Zn alloy. Under potentiostatic control the dissolution mechanism depends on the electrode potential and changes from exclusive dissolution of zinc to simultaneous dissolution of both components with preferential dissolution of zinc. The latter decreases, as the electrode potential becomes more positive.     

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.     

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.     

A simple procedure for the quantitative microdetermination of rhamnose

Summary A simple spectrophotometric procedure for microdetermination of rhamnose is described. It is based on breakdown of the sugar with sulphuric acid followed by treatment withp-hydroxydiphenyl. The coloured product is measured spectrophotometrically at 560 nm. A linear relationship exists between the amount of rhamnose (10-0g–) and the absorbance. The method is recommended for determination of rhamnose in samples containing rhamnose, different neutral sugars, amino-sugars, sugar alcohols, uronic acids, and muramic acid.

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Zusammenfassung Ein einfaches spektralphotometrisches Verfahren zur Mikrobestimmung von Rhamnose wurde beschrieben. Es beruht auf der Spaltung des Zuckers mit Schwefelsäure und nachfolgender Behandlung mit p-Hydroxydiphenyl. Das gefärbte Reaktionsprodukt wird spektralphotometrisch bei 560 nm gemessen. Die Extinktion steht mit der Rhamnosemenge in linearer Beziehung. Das Verfahren wird für die Rhamnosebestimmung in Proben empfohlen, die verschiedene Neutralzucker, Aminozucker, Zuckeralkohole, Uronsäuren und Muramsäure enthalten.

     

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.     

Elektronenspektren einiger Thioamide und ihrer S- und N-Derivate

Zusammenfassung Wir diskutieren und veröffentlichen die Elektronenspektren einiger Thioamide und die einiger S- und N-Derivate (N-Aryl-, N-Methyl-N-aryl-, S-Methyl-N-aryl-, N-Acyl-) davon.

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The electronic spectra of some thioamides and their S- and N-derivatives (N-aryl, N-methyl-N-aryl, S-methyl-N-aryl, N-acyl) have been reported and discussed.

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Aus der vonN. Stojanac eingereichten Dissertation, die einen Teil der zur Erlangung des Titels eines Doktor der Chemie (Ph. D.) der Universität Zagreb gestellten Anforderungen erfüllt.