Effect of lanthanides on the relaxation rates of 89Y and 29Si in yttrium silicon oxynitride phases.

Additions of paramagnetic lanthanides are found to increase the relaxation rates of both 89Y and 29Si in the yttrium silicon oxynitride compounds Y2Si3N4O3 (N-melilite) and Y4Si2O7N2 (J-phase), allowing the observation of previously unreported 89Y magic-angle spinning nuclear magnetic resonance spectra of these phases. The dependence of the 89Y and 29Si relaxation rates was determined as a function of Yb3+ and Gd3+ concentration. Both the 29Si and 89Y resonances become broader with increasing Yb concentration, but at all lanthanide concentrations the 89Y spectrum of J-phase is broader than that of N-melilite, possibly due to a greater distribution of Y site geometries in the former. At concentrations below about 360 mumol g-1, the lanthanide ions appear to be incorporated in the lattice, but are not involved in covalent bonding to Y or Si. The effect of a series of lanthanides on the 89Y and 29Si relaxation rates and line widths is presented in terms of the lanthanide spin quantum numbers and magnetic moments. The most effective lanthanide was found to be Eu3+, giving fast relaxation (particularly for 89Y) and sharp lines.

Titanium carbide, nitride and carbonitrides: a 13C, 14N, 15N and 47,49Ti solid-state nuclear magnetic resonance study.

The first 47,49Ti, 13C, 14N and 15N solid-state nuclear magnetic resonance (NMR) spectra of titanium carbide, nitride and a series of cubic carbonitrides have been obtained under both static and magic-angle spinning (MAS) conditions. The 15N samples were isotopically enriched by gas-solid exchange at 1000 degrees C in a closed system. The Ti spectra of the carbide and nitride are sharp, reflecting the well defined cubic symmetry of these compounds, but become considerably broadened in the carbonitride series, with the spectra being approximately the sum of TiC and TiN together with some small electric field gradient (EFG) effects. The resonance positions and widths of all the NMR spectra change as carbon is progressively replaced by nitrogen. A relationship is observed between the 13C chemical shift and the nitrogen content of the carbonitrides, suggesting a possible NMR method for estimating the composition of these compounds. Although electron paramagnetic resonance (EPR) spectra of all these compounds show typically metallic behaviour, the NMR spectra show few effects attributable to conduction electrons, probably due to the lack of s-orbital contributions to the conduction band.

Rapid determination of glyphosate in postmortem specimens using 31P NMR.

Glyphosate was quantified, using 31P NMR, in postmortem blood, liver, and urine specimens taken from two suicide victims. Apart from addition of D2O to give an NMR lock signal, the only pretreatment required of any of the specimens was an enzymic digestion of the liver. Glyphosate was confirmed by its characteristic 31P chemical shift and proton spin coupling and by a downfield shift on addition of NH4OH. Quantitation can be achieved either by comparison with an external standard or by spiking the specimen with glyphosate. Levels of 1 mg/mL could be detected in less than a minute.