COMPARISON BETWEEN INFRARED AND ULTRAVIOLET-LASER ABLATION AT ATMOSPHERIC-PRESSURE - IMPLICATIONS FOR SOLID SAMPLING INDUCTIVELY-COUPLED PLASMA SPECTROMETRY

The efficiency of laser solid sampling was investigated as a function of several experimental parameters under experimental conditions similar to those used for laser ablation (LA) inductively coupled plasma spectrometry. This was done by studying the amount of material removed as a function of melting temperature of the (metallic) matrix material, laser wavelength and laser energy, and by studying the plasma ignition in air and argon buffer gases as a function of laser wavelength. It was found that direct LA is the major process responsible for the removal of material in the case of a UV laser, as opposed to with an IR laser, where shielding of the laser radiation by the absorbing plasma limits direct LA and increases the temperature of the plasma. The consequences of this difference between IR and UV laser radiation are considerable and lead to a superior performance of UV laser sampling in every analytical aspect: reproducibility, matrix effects, quantification, spatial resolution and sensitivity.