Electrochemical oxidation of some tetrahydropteridine derivatives at the platinum electrode

6 and 7-substituted 2-amino-4-hydroxy-5,6,7,8-tetrahydropteridines are oxidized at a platinum electrode in several waves in the potential range between hydrogen and oxygen evolution potentials. The electrode process in the first (main) anodic wave was investigated in more detail using a stationary and rotating disc platinum electrode. The process in this wave is “semireversible” with an exchange of two electrons. The standard rate constants of this reaction were determined. The oxidation product is deactivated by an irreversible chemical reaction. Some of the products block the surface of the electrode.     

Near-edge X-ray absorption fine structure study of disordering in Gd2(Ti1-yZry)2O7 pyrochlores

Disorder in Gd2(Ti(1-y)Zry)2O7 pyrochlores, for y = 0.0-1.0, is investigated by Ti 2p and O 1s near-edge X-ray absorption fine structure spectroscopy. Ti(4+) ions are found to occupy octahedral sites in Gd2Ti2O7 with a tetragonal distortion induced by vacant oxygen sites. As Zr substitutes for Ti, the tetragonal distortion decreases, and Zr coordination increases from 6 to 8. The migration of oxygen ions from 48f or 8b sites to vacant 8a sites compensate for the increased Zr coordination, thereby reducing the number of vacant 8a sites, which further reduces the tetragonal distortion and introduces more disorder around Ti. This is evidence for simultaneous cation disorder with anion migration.     

Determination of 6-keto-PGF1 alpha, 2,3-dinor-6-keto-PGF1 alpha, thromboxane B2, 2,3-dinor-thromboxane B2, PGE2, PGD2 and PGF2 alpha in human urine by gas chromatography-negative ion chemical ionization mass spectrometry

A method for quantification of 6-keto-PGF1 alpha, 2,3-dinor-6-keto-PGF1 alpha TXB2, 2,3-dinor TXB2, PGE2, PGD2 and PGF2 alpha in human urine samples, using gas chromatography-negative ion chemical ionization mass spectrometry, is described. Deuterated analogues were used as internal standards. Methoximation was carried out in urine samples which were subsequently applied to phenylboronic acid cartridges, reversed-phase cartridges and thin-layer chromatography. The eluents were further derivatized to pentafluorobenzyl ester trimethylsilyl ethers for final quantification by gas chromatography-mass spectrometry. The overall recovery was 77% for tritiated 6-keto-PGF1 alpha and 55% for tritiated TXB2. Urinary levels of prostanoids were determined in a group of six volunteers before and after intake of the thromboxane synthase inhibitor Ridogrel, and related to creatinine clearance.     

Automatisierte Jodbestimmung in R?ntgen-Kontrastern

Zusammenfassung Eine neue Dehalogenierungs-Methode mit 0,15% Natriumborhydrid in 1 N Natronlauge und Palladium als Katalysator (2 m mit Palladium beschichtetes Messing-Reaktionsrohr) ermöglicht die Ionisierung des organisch gebundenen Jods in 5 min bei 85° C. Anschließend wird die wäßrige Lösung mit Schwefelsäure angesäuert, das Jodid mit Nitrit zu Jod oxydiert und photometrisch bei 455 nm gemessen. Die Prozedur läuft in einem Technicon AutoAnalyzer.

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Automatic iodine determination in X-ray contrasters

A new dehalogenation method with 0.15% sodium tetrahydroborate in 1 N sodium hydroxide and palladium as a catalyst (2 m Pd coated brass reaction tube) makes possible the ionisation of the organic bound iodine in 5 min at 85° C. Subsequently the aqueous solution is made acidic with sulphuric acid, the iodide oxidized to iodine with the aid of nitrite and then measured photometrically at 455 nm. The procedure is carried out in a Technicon AutoAnalyzer.

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Wir danken Herrn Marcel Bonnafé für seine Mithilfe und die wertvollen Ratschläge bei der Aufstellung der Apparatur.     

Effective on-line coupling of HPLC and flame-AAS by means of hydraulic high pressure nebulization

Summary Hydraulic high pressure nebulization is used as an effective way of on-line coupling of HPLC to flame-AAS for speciation of metal compounds in the ng range. Compared to coupling with a conventional nebulizer a signal enhancement by a factor of 7.5 (peak height) and 10.1 (peak area) for copper is obtained. Using an injected volume of 50 μL the detection limits for Cu, Fe, Ni and Cd are below 0.1 μg/mL (=5ng) and for Mg below 0.01 μg/mL (=0.5ng). The effects of HPLC flow-rate and nebulization nozzle diameter on the signal peak height have been investigated. The performance of the system is demonstrated using speciation of iron. A base-line separation of Fe(II) and Fe(III) is achieved within two minutes. Also species changes (Fe acetate to Fe citrate) can be analysed using the proposed system.     

DECAY KINETICS OF N, N, N', N-TETRAMETHYLBENZIDINE PHOTOCATIONS IN FROZEN MICELLAR SOLUTION OF CETYLTRIMETHYLAMMONIUM BROMIDE

Abstract—
After UV irradiation of rapidly frozen solutions of N, N, N', N' -tetramethylbenzidine (TMB) in dilute aqueous micellar cetyltrimethylammonium bromide at 80 K, the ESR signal corresponding to the TMB⁺ cation was detected indicating photoionization. This signal was monitored as a function of time at various temperatures between 80 K and 260 K. On a timescale of a few days the signal decayed to a plateau value that was stable for months. Two distinct second-order processes for the decay from the initial to the plateau value were observed: one prevailing at low temperatures with an activation energy of 0.6 kJ/mol, and one prevailing at T > 220 K with an activation energy of 13 kJ/mol. By means of spin probe investigations the latter process was shown to be connected with a local softening of the region adjacent to the micellar surface.