Coulometrische Wismutometrie

Zusammenfassung Durch elektrolytische Oxydation einer Bi-Anode in gesättigter NaCl-Lösung können Bi³⁺-Ionen in Lösung gebracht werden. Dieser Prozeß ermöglicht die coulometrische Bestimmung anwesender Anionen, die schwerlösliche Bi-Verbindungen bilden.Es wurden Semimikro- und Mikrobestimmungen von Phosphationen durch elektrolytisch erzeugte Bi³⁺-Ionen bei konstanter Stromstärke ausgeführt. Die Endpunktbestimmung erfolgte amperometrisch bei konstantem Potential mit einer Indikatorelektrode — tropfende Quecksilberelektrode — und mit einer gesättigten Kalomelelektrode als Bezugselektrode. Die coulometrische Wismutometrie bietet eine weitere Möglichkeit der coulometrischen Eichung volumetrischer Lösungen im Sinne des seinerzeitigen Vorschlags vonTutundi.

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Summary Bi³⁺ ions can be brought into solution through electrolytic oxidation of a Bi-anode in saturated NaCl solution. This process makes possible the coulometric determination of the anions present that yield difficulty soluble bismuth compounds.Semimicro- and micro-determinations of phosphate ions were made via Bi³⁺-ions produced electrolytically at constant current strength. The endpoint was determined amperometrically at constant potential with an indicator electrode-dropping mercury electrode-and with a saturated calomel electrode as reference electrode. The coulometric bismuthometry affords a further possibility of the coulometric standardization of volumetric solutions in the sense of the proposal previously advanced byTutundi.

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Résumé On peut utiliser les ions Bi³⁺ en solution par oxydation électrolytique d'une anode en bismuth, en solution de chlorure de sodium saturée. Ce procédé permet le dosage coulométrique des anions présents qui forment des composés peu solubles avec le bismuth.On a mis au point le dosage semimicro et micro des ions phosphates par les ions Bi³⁺ formés électrolytiquement sous intensité constante. On détermine par ampérométrie le point équivalent à potentiel constant à l'aide d'une électrode indicatrice — électrode de mercure à goutte pendante —et avec une électrode au calomel saturée comme électrode de référence. La «bismuthométrie» coulométrique offre de grandes possibilités pour l'étalonnage coulométrique de solutions volumétriques, suivant l'idée queTutundi a émise en son temps.

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Vorgetragen beim Symposium für analytische Chemie in Graz, 29. September bis 1. Oktober 1965.

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Wir danken Herrn Dipl.-Ing.Vladimir Pantovi für seine Hilfe bei unserer experimentellen Arbeit.     

The rate difference between the weak decays of t and in supersymmetry

We find that the CP-violating asymmetry

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at the one-loop order within the minimal supersymmetric extension of the standard model is of the order of few percent for maximal CP violation. It could be measured by considering the rate difference in the one-lepton events.     

DPPH as a primary standard for quantitative EPR spectrometry

The present studies are concerned with the influence of the nature of the solvent on the time-dependent stability of the absorption maxima of the free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) at 520 nm as well as the intensity of its EPR spectrum. The correlation between these two characteristics of DPPH, the behaviour of which is found to be unpredictably strange, unambiguously shows that the problem for calibration of DPPH in order to be used as a primary standard for quantitative EPR spectrometry purpose is not solved yet. This problem needs additional studies in order to find exact methods for examination of the data concerning DPPH quantitative characteristics before its use.     

A new membrane electrode system with iodide-selective properties

The strongly basic anion-exchange resin Dowex 2 when saturated with triiodide and placed in a gel layer in a glass tube acts as an electrode for iodine, as does a platinum wire electrode. When the gel membrane is placed with a platinum electrode in an iodide solution, the anion-exchange resin adsorbs iodide selectively, and a decrease in the potential of the membrane electrode is caused. The arrangement can be used as an iodide-selective electrode, which shows a linear response over the pI^-range 1–5 and an excellent selectivity for iodide over other halides.     

A highly selective and sensitive method for identification of gold

Summary A highly sensitive method for detection of gold, almost free from interferences, is described. The reaction is performed on a short column of anion-exchange resin Dowex 1 X8 (100–200 mesh) in iodide form. To the test solution containing 0.13g/ml of gold(III) is added Sb-solution (weight ratio Au: Sb=1 200) and the mixture is then passed through the resin, followed by 1N NaOH. A crimson colour appearing within 2–3 min indicate gold. Many metal ions, including Pt-metals, Tl(I), Tl(III), Ir(IV), In (III), Ga(III), Cu(II), Cd(II), Zn(II), Pb(II), Fe(III), Mn(II), Co(II), Ni(II), Hg(II), As(III) do not interfere. In the presence of 50-fold excess of Ag(I) or Bi(III) there is no colour because of the formation of a precipitate on the resin.

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Zusammenfassung Ein hochempfindliches und selektives Verfahren zum qualitativen Gold-nachweis wurde vorgeschlagen. Die Reaktion wird in einer 10 mm hohen Anionenaustauschersäule Dowex 1 X8 in Jodidform durchgeführt. Zu der aufgetragenen Probelösung fügt man Sb(III) und (V) (im Verhältnis Au: Sb= 1 200) und versetzt nachher auf der Säule mit 1-n NaOH. Nach einigen Minuten entsteht um die Harzkörner eine himbeerrote Färbung. Pt-Metalle, Tl(I), Tl(III), Ir(IV), In(III), Ga(III), Cu(II), Cd(II), Zn(II), Pb(II), Fe(III), Mn(II), Co(II), Ni(II), Hg(II), As(III) stören nicht; Ag(I) und Bi(III) stören gleichfalls nicht, solange sie in nicht mehr als 50facher Menge neben Gold vorliegen. Bei höheren Konzentrationen setzen sie sich als unlösliche Jodide um die Harzkörner ab und stören. Die Nachweisgrenze der Reaktion liegt bei 0,13g/ml.

     

Geochemical investigation of alluvial sediments: validation of ICP-OES determination of heavy metals. A case study from the Utrata River Valley (central Poland)

The development and validation of a reliable analytical procedure for the determination of selected metals (Cd, Cr, Cu, Pb, Zn and Mn) in sediments accumulated in the Utrata River (Poland) is described. The aqua regia extraction followed by inductively coupled plasma optical emission spectrometry (ICP-OES) was used for this purpose. The optimized analytical procedure was validated, and adequate quality control actions were implemented in order to provide reliable data. The precision under’ within-laboratory’ reproducibility conditions was estimated from duplicate analysis. Certified reference material (CRM) was used in order to evaluate the accuracy of the results regarding the sewage sludge amended soil CRM 143R. The detection limits for all elements of interest were well-below their content in the investigated sediment samples. The obtained reliable data could be used for assessment of the relationship between human economic activity in the past and the geochemical features of the sediments.     

Morphology of Polyethylene Foamed Crosslinked Specimens made by Hot Mold Injection Molding

Abstract

Foamed and crosslinked specimens of polyethylene made by hot mold injection molding were investigated. A combination of PELD, dicumilperoxide and azodicarbonamide was used. The three components were mixed and granulated in an extruder-granulator at temperature 100—120°C. The degree of crosslinking was calculated by equilibrium strain ?_r determined at temperature 140°C and pressure stress σ_p=0.045 MPa. The same parameter was evaluated by thermomechanical curves. The degree of crystal-linity was determined by DSC-kinetics of a nonisothermal melting and crystallization. The morphology was investigated by a polarized microscope MIN 8.

It is established that a part of polymer crystallizes as spherulites. The spherulites can observed with crossed polarizers. The samples on the whole are not oriented. There exists only a local orientation around the edge of the bubbles which is proved by the observed bright regions. The number of the spherulites decreases with the increase of crosslinking degree. This also conforms with the degree of crystallinity which decreases with the increase of the crosslinking degree.     

Morphology and Orientation of PP-Structural Foam Moldings

Abstract

An experimental study was conducted to investigate the interaction between the macrostructure and morphology of PP-structural foam moldings made by gas-counter pressure process by egression of foamed melt from the core of the molding. The structural foam moldings, center-gated cylindrical plate “disc” (diameter 1800 mm. high 11 mm) were produced on an in-line injection molding machine KuASY 800/250, varying the shot weight and melt temperature. The polymer used was isotactic polypropylene “Buplen” 7523 with 1 wt% chemical blowing agent (azodicarbonamide) added. The morphology, orientation, and processes of non isothermal phase transition have been studied using polarized optical microscopy, SALS, DSC and birefringence. Samples were cut from the discs at different distances from the gate. The presence of a two-layered structure was observed in the solid skin: an outer smectic layer and an inner particular crystalline layer. The thickness of the smectic layer and size of spherulites from skin to the foamed core were determined. The orientation in radical and tangential direction of the flow and perpendicular to the disc surface were studied in mold filling and egression stage. The fixed orientation in final moldings is a complex picture of bubble growth, bubble orientation and shear flow. It was found that the radical orientation decreases with the distance from the gate. Maximum orientation is located in the solid skin, and minimum in the foamed core, and was shown by means of a birefringence profile.     

Fast and easy multiresidue method employing acetonitrile extraction/partitioning and "dispersive solid-phase extraction" for the determination of pesticide residues in produce

A simple, fast, and inexpensive method for the determination of pesticide residues in fruits and vegetables is introduced. The procedure involves initial single-phase extraction of 10 g sample with 10 mL acetonitrile, followed by liquid-liquid partitioning formed by addition of 4 g anhydrous MgSO4 plus 1 g NaCl. Removal of residual water and cleanup are performed simultaneously by using a rapid procedure called dispersive solid-phase extraction (dispersive-SPE), in which 150 mg anhydrous MgSO4 and 25 mg primary secondary amine (PSA) sorbent are simply mixed with 1 mL acetonitrile extract. The dispersive-SPE with PSA effectively removes many polar matrix components, such as organic acids, certain polar pigments, and sugars, to some extent from the food extracts. Gas chromatography/mass spectrometry (GC/MS) is then used for quantitative and confirmatory analysis of GC-amenable pesticides. Recoveries between 85 and 101% (mostly > 95%) and repeatabilities typically < 5% have been achieved for a wide range of fortified pesticides, including very polar and basic compounds such as methamidophos, acephate, omethoate, imazalil, and thiabendazole. Using this method, a single chemist can prepare a batch of 6 previously chopped samples in < 30 min with approximately 1 dollar (U.S.) of materials per sample.     

Gels with exceptional thermal stability formed by bis(amino acid) oxalamide gelators and solvents of low polarity

Some bis (amino acid) oxalamide gelators form common thermo-reversible gels with various organic solvents but also gels of exceptional thermal stability with some solvents of medium and low polarity; the latter gels can be heated up to 50 degrees C higher temperatures than the bp of the solvent without apparent gel-to-sol transition.