Pb/U fractionation during Nd : YAG 213 nm and 266 nm laser ablation sampling with inductively coupled plasma mass spectrometry

Elemental fractionation during laser ablation sampling was investigated by measuring Pb/U ratios in NIST 610 synthetic glass. Two Nd:YAG lasers with w avelengths of 213 and 266 nm were used to ablate the sample into an inducti vely coupled plasma mass spectrometer. Pb/U fractionation was observed to b e similar for both laser wavelengths, and dependent on the irradiance. For representative Pb/U measurements, the necessary laser irradiance should be >0.6 GW/cm(2). However, if the laser beam is initially focused close to the sample surface, fractionation increases and is influenced by the formation of a crater during repetitive pulsing at a single sample location. As the ratio of crater depth to radius increases, plasma sampling and/or an effect ive irradiance decrease could cause additional fractionation. A good correl ation was found between the fractionation of 14 elements in NIST 610 glass and the logarithms of their oxide melting temperatures.