Effects of wavelength, pulse duration and power density on laser activation of glassy carbon electrodes

The hypothesis that laser activation of glassy carbon (GC) electrodes is thermally driven was investigated by comparing simulated surface temperatures for several lasers and experimental conditions. Assuming no phase changes, the surface temperature vs. time profile for a laser pulse striking a GC electrode was predicted by finite difference simulation. It was predicted that peak surface temperature depends on power density, wavelength, pulse duration and the optical properties of the carbon. Experimentally, laser activation is weakly wavelength dependent for ascorbic acid and Fe . The surface temperatures required for activation were consistent for different lasers, supporting the conclusion that laser activation is thermally driven. Furthermore, predicted surface temperatures during activation were below the melting point of carbon but well above the boiling point of water. The results should be useful for predicting the effectiveness of different laser conditions on electron transfer activation.     

Comparison of dissolution methods for the determination of potassium in rocks and minerals by atomic absorption spectrometry

Lithium metaborate fusion and hydrofluoric acid dissolution methods used before the flame emission or atomic absorption spectrometric determination of potassium in rocks and minerals are compared with regard to accuracy and precision. Possible contamination by potassium in borosilicate glassware was avoided by the use of platinum or polyethylene vessels; solutions were prepared and measured by weight instead of volume. Separation of potassium by cation-exchange chromatography enabled potassium in all solutions of a given sample to be measured against one set of standard solutions. When the various dissolution methods were used carefully, the results did not differ in precision. Significant systematic errors were not detected; in particular, potassium was not lost by volatilization during fusion for 15 min with lithium metaborate at 9OO°C.     

Heterogeneous binding of lipoteichoic acid to the surface of titanium dioxide as determined with 31P solid-state NMR spectroscopy

The adsorption of lipoteichoic acid onto the surface of titanium dioxide is shown to be heterogeneous. 31P CPMAS solid-state NMR reveals two distinct phosphate species. The chemical shift anisotropy, asymmetry parameter, and rotating-frame spin-lattice relaxation suggest that 50% of the phosphates are bound to the surface. The remaining phosphates also exhibit restricted molecular motion, but do not have a direct surface bond.