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A new approach to the quantification of the optical emission signals from a laser produced plasma in air at atmospheric pressure is described. It is based on a simple analytical model giving intensity of the emission lines as a function of the vaporized mass and the plasma excitation temperature. Under the hypothesis of a stoichiometric ablation process, these two parameters are presumed to be responsible for the matrix effects observed when the composition of the sample is changed. Under the experimental conditions chosen it is demonstrated that the acoustic signal emitted by the plasma is proportional to the vaporized mass and that the excitation plasma temperature can be controlled using the line ratio of a given element chosen as a ‘temperature sensor’. Normalization of the emission signals by these two parameters allows for an efficient correction of the matrix effects. Results obtained on a series of aluminium alloys, steel and brass samples demonstrate, for the first time, the possibility of matrix independent analysis with LA-OES with an accuracy of a few percent.

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.