Purity assessment problem in quantitative NMR--impurity resonance overlaps with monitor signal multiplets from stereoisomers.

This paper describes the situation that can emerge when the signals to be evaluated in quantitative NMR measurements-so-called "monitor signals"--consist of several resonance lines from the stereoisomers of the analyte in addition to an impurity signal underneath. The monitor signal problem is demonstrated in the purity assessment of two samples of 2-(isopropylamino)-4-(ethylamino)-6-chloro-1,3,5-triazine (atrazine), a common herbizide which served as analyte in a CCQM intercomparison. It is shown that, in DMSO-d6 solution, a mixture of stereoisomers leads to several individual overlapping singlets, which are further split by spin-spin coupling.

Uric acid monohydrate--a new urinary calculus phase.

In our laboratory more than 100,000 urinary calculi have been analysed since 1972. Amongst this huge sample, 15 specimens originating from a total of eight patients were observed showing similar characteristics but escaping unambiguous identification with any of the substances that have been described so far in urinary concrements. Therefore, the unknown substance was submitted to a more extended analytical regimen.

Characterization of silsesquioxanes by size-exclusion chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

Liquid chromatography in combination with spectroscopic methods like matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) or nuclear magnetic resonance (NMR) spectroscopy is a powerful method to characterize silsesquioxanes and silsesquioxane mixtures. As new examples, the formation of silsesquioxyl-substituted silsesquioxanes [(n-octyl)(7)(SiO(1.5))(8)](2)O and [(n-octyl)(7)(SiO(1.

Non-selective signal loss in the 13C CPMAS NMR spectra of soil organic matter. Investigations of particle size fractions.

In 13C cross-polarisation magic angle spinning (CPMAS) spectra of soil samples, the paramagnetic soil constituents partially discriminate against the signal intensity of the 13C atoms. The aim of the present study was to check to what extent this signal depression depends on the paramagnetic ion content and if it is selective for a certain kind of carbon species. The spectra of a variety of particle size fractions of five quite different soils were recorded.