The determination of microgram amounts of orthophosphate using ion-selective electrodes

Summary The potentiometric titration ofg amounts of orthophosphate with lead perchlorate using a lead ISE, and with silver nitrate using a silver sulfide ISE, was investigated. With 0.001N lead perchlorate the practical limit of the determination is approximately 10g (0.3mol) of phosphorus. Microgram amounts of phosphate require the application of a small polarizing current to the lead ISE to enhance the potential breaks near the endpoint.Previously reported titrimetric methods for orthophosphate with silver nitrate were reinvestigated using a silver sulfide ISE. The borate-buffered system proved superior to the sodium acetate-methanol system when a partially non-aqueous medium of 60–70% methanol was used. With the borate-buffered system, 0.005N silver nitrate can be used, while it cannot be used in the sodium acetate-methanol system. Also, considerably larger amounts of sulfate and fluoride can be tolerated in the borate-buffered system. The sequential determination of halides and phosphate is feasible in this system.

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Zusammenfassung Die potentiometrische Titration von Mikrogrammengen Orthophosphat mit Bleiperchlorat und einer bleispezifischen Elektrode bzw. mit Silbernitrat und einer silberspezifischen Elektrode wurde untersucht. Mit 0,001-n Bleiperchlorat liegt die praktische Grenze der Bestimmbarkeit bei etwa 10g (0,3Mol) Phosphor. Bei Mikrogrammengen Phosphat muß man an die bleispezifische Elektrode einen schwachen Polarisationsstrom anlegen, um den Potential-Knick nahe dem Endpunkt zu verstärken.Früher veröffentlichte Titrationsmethoden für Orthophosphat mit Hilfe von Silbernitrat wurden neuerlich mit einer Silbersulfidelektrode bearbeitet. Ein Boratpuffersystem erwies sich der Pufferung mit Natriumacetat-Methanol überlegen, wenn in 60–70%igem Methanol gearbeitet wird. In boratgepufferter Lösung kann man mit 0,005-n Silbernitrat titrieren im Gegensatz zu acetat-methanolischer Lösung. Auch können wesentlich größere Mengen Sulfat und Fluorid im boratgepufferten System toleriert werden. Halogenide und Phosphat können in diesem Milieu nacheinander bestimmt werden.

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This work was performed under the auspices of the U. S. Atomic Energy Commission.     

Deactivation of vibrationally excited CD3H using laser-induced fluorescence

Infrared fluorescence observed after exciting to ν₆ (ν=1) of CD₃H with a Q-switched CO₂ laser yields the exponential deactivation rate constant of 0.84 ms^?1 torr^?1. Rate constants for deactivation of CD₃H by rare gases vary from 1.4 (for He) to 0.029 (for Xe) ms^?1 torr^?1.     

Determination of inositol phosphate esters in lake sediments

A procedure for the determination of the total inositol polyphosphate content of lake sediments is presented and evaluated. This technique involves extraction with NaOH, cleanup of the extract, and isolation and identification of two groups of inositol phosphate esters by ion-exchange chromatography. Radioisotope dilution is employed to correct for losses during the extraction, cleanup and isolation steps. Recoveries of the radiotracer inositol phosphates have averaged 85% during the analysis of approximately 40 calcareous and non-calcareous sediment samples and more than 20 soil samples.     

Die Hydrolyse von Phospholinsäureamiden

Hydrolysis of Amides of Phospholinic Acid The acid catalysed hydrolysis of (= OAP, R = organic substituent) has been investigated kinetically. Provided the pH remains constant, the hydrolysis is a first order reaction. From the temperature dependance of the rate constant the activation energy E_a as well as the thermodynamic data ΔH* and ΔS* have been calculated. In comparison to the compound with R = H aromatic substituents and additional the t-butyl group enhance E_a whilst aliphatic substituents included the benzyl group diminish E_a. The first step of the reaction is a protonation at the oxygen or nitrogen resulting in the formation of an equilibrium. After the determination of the basicity constant K_A of some OAPs it was possible to calculate the respective rate constants of the rate determining step of the reactions and the corresponding thermodynamic data E_F, ΔH and ΔS. It is assumed that the mechanism of the hydrolysis takes place according to the same scheme which has been assumed for the hydrolysis of cyclic esters of the phosphinic acid by Ugi [1] and colaborators.     

Complexation of Cu2+ by Binucleating Macrocycles Containing the N6 Donor Set

The hexadentate ligands 1,4,7,12,15,18-hexaazacyclododecosane ([2]aneN₆) and 1,4,7,14,17,20-hexaazacyclohexacosane ([26]aneN₆) both form eight complexes with Cu²⁺, three of them being binuclear. The corresponding stability constants have been determined potentiometrically, and the electronic absorption spectra have been obtained from spectrophotometric data. Possible interactions of the Cu²⁺ pairs in the three binuclear complexes have, in addition, been investigated by ESR and and linear -sweep voltammetry (LSV). The binuclear complex of [22]aneN₆ with one addditional OH group is exceptionally stable, ESR-silent, and the results of the LSV-experiments are characteristically different from those of the other binuclear complexes with both ligands. This indicates that [22]aneN₆ forms a very stable hydroxo-bridged binuclear Cu²⁺ complex Cu₂L(OH)³⁺, whereas in the case of [26]andN₆ no bridged Cu²⁺ pair exists.