The limit of detectability in X-ray electron-probe microanalysis

Summary The definitions given by various authors for the limit of detectability are compared and their relationship to the basic measurements (especially the background value) is explained. A new definition is derived on the assumption that the relative standard deviation must not exceed 33.3% if negative results are to be avoided. Negative results may still appear, but only very rarely. The properties of this limit of detectability are discussed, together with the effect of making multiple measurements of the background and peak.

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Zusammenfassung Die von verschiedenen Autoren angegebenen Definitionen der Nachweisgrenze wurden verglichen und deren Beziehung zu den Bezugsmessungen (besonders des Untergrundes) wurde erklärt. Eine neue Definition wurde von der Annahme abgeleitet, daß die relative Standardabweichung 33,3% nicht überschreiten darf, sollen negative Resultate vermieden werden. Solche können zwar auftreten, aber nur sehr selten. Die Eigenschaften dieser Nachweisgrenze wurden ebenso wie die Auswirkung mehrfacher Messungen des Untergrundes und der Peaks diskutiert.

     

Catalytic effect of metal ions on photochemical reactions of molecular oxygen, III. Photochemical autoxidation of sulfite catalyzed by manganese(II) ions

The rate of photoinitiated autoxidation of sulfite is influenced by manganese(II) ions even in trace concentrations. An increase in the concentration of manganese(II) ions in the reaction system increases the quantum yield of the photoinitiated reaction.

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(II), - . (II) - .

     

Calculation of cross sections for positron-Ar collisions

The three-body classical trajectory Monte-Carlo (CTMC) method is used to investigate positron-argon atom collisions. The total ionization cross sections are presented along with singly and doubly differential cross sections. The existence of the cusp-like peak in the triply differential electron and positron spectra at positron impact is predicted.     

Analytische Aspekte der Oxydation organischer Stickstoffverbindungen mit Chromsäure. XXVIII

Zusammenfassung Die schon früher beschriebene gasvolumetrische Methode zur N-N-Gruppenbestimmung durch Oxydationsaufschluß mit Chromsäure wurde zur Bestimmung des heterocyklischen Stickstoffes in Indazolinonderivaten mit Erfolg benützt und dadurch weiter die allgemeine Anwendbarkeit der Methode bestätigt. Enthält die Substanz gleichzeitig Amino- oder Nitrogruppen, können diese aus derselben Einwaage als Ammoniak bzw. Salpetersäure bestimmt werden.

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

Summary The gas volumetric method for determining N-N groups by oxidative fusion with chromic acid (which has already been described previously) was successfully employed to determine the heterocyclic nitrogen in indazolinone derivatives. The general applicability of the method was thereby confirmed. If the substance contains amino or nitro groups at the same time, these can be determined in the same sample as ammonia or nitric acid.

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XXVII. Mitteilung, siehe¹.     

Iodide-promoted uncatalyzed bromate oscillators

Iodide ions—in a rather narrow concentration range—induce some of the uncatalyzed bromate oscillators to a more pronounced oscillatory activity: the number of oscillations increases considerably and the overall rate of the chemical reaction drops about an order of magnitude. Preliminary suggestion is made on the mechanism of iodide-induced oscillatory reactions.

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— — : . - .

     

Tröger's base scaffold in racemic and chiral fashion as a spacer for bisdistamycin formation. Synthesis and DNA binding study

‘Head-to-head’ oligo-N-methylpyrrole peptide dimers linked by a methano[1,5]diazocin scaffold are presented in racemic as well as chiral fashion. Their DNA binding activities were assayed on calf thymus DNA, poly(dA-dT)₂, and poly(dC-dG)₂ by NMR and ECD spectroscopies, and fluorescence probe displacement assay. The presented dimers prefer AT sequences, but show higher affinity to poly(dC-dG)₂ than distamycin A. The (4R,9R) configuration of methanodiazocin bridge was found to be better suited for interaction with ct-DNA and poly(dA-dT)₂ than (4S,9S) configuration.     

High-performance liquid radiochromatography: Its application for stability study of [3H] stobadin

An HPLC method was developed for studying the stability of [³H] stobadin stored in physiological saline or buffers at various pH. Optimum conditions for the separation of degradation products were elaborated. A high-performance liquid chromatograph equipped with a radioactivity detector was used.     

Multiparametric curve fitting-I Computer-assisted evaluation of chelatometric titrations with metallochromic indicators

A curve-fitting procedure has been developed for the photometric complex-formation titration of the metal-indicator complex MIn(N) which is assumed to predominate in solution. By means of a least-squares procedure the following five parameters were determined: the end-point, the absorbance of the indicator complex A(M)XXX. the indicator concentration CXXX, the stability constants and, if possible, k(MY) . A modified version of Sillen's Letagrop Vrid has been used for the mathematical-statistical approach of the non-linear model based upon the non-transformed function A = f(v). Additional information is obtained about the goodness of fit, indicating whether the chosen model with predominance of MIn(N) is correct or not. The use of the program is demonstrated by application to chelatometric microtitrations of zinc and lead with EDTA, using Naphthylazoxine 6S and SNAZOXS as metallochromic indicators.