In the present work a detailed study has been performed on the effect of the matrix on the limit of detection (LOD) and the plasma parameters of the laser induced breakdown spectroscopy (LIBS) technique. The LOD of magnesium, silicon, manganese and copper as minor elements was evaluated in aluminium standard sample alloys compared to the values of the LOD of the same elements in standard steel alloys. The effect of changing the matrix on the laser induced plasma plume parameters, namely the plasma temperature T_e and the electron density N_e, has been also studied. Calibrations were achieved for the four elements with linear regression coefficients between 98–99% on average. According to the obtained results Mn and Cu have the lowest LOD in the steel alloy matrix, while Mg has much lower LOD in the aluminium alloy matrix. These results may be interpreted in view of the compatibility of the physical properties of the elements existing in the same matrix. Approximately similar electronic structure and values of melting point, density, atomic weight, etc., may facilitate better conditions for energy transfer within the matrix. From the application view point, it is possible for LIBS in the on-line industrial process control to follow up only a single element (that with the lowest LOD in such matrix) as a marker for the correct alloying in metals and mixing in pharmaceuticals.

In order to improve the performance of the LIBS technique – in particular its sensitivity, reproducibility and limit of detection – we studied the effect of applying a static electric field with different polarities on the emission spectra obtained in a typical LIBS set-up. The physical parameters of the laser-induced plasma, namely the electron density Ne and the plasma temperature Te, were studied under such circumstances. In addition to the spectroscopic analysis of the plasma plume emission, the laser-induced shock waves were exploited to monitor the probable changes in the plasma plume dynamics due to the application of the electric field. The study showed a pronounced enhancement in the signal-to-noise (S/N) ratio of different Al, neutral and ionic lines under forward biasing voltage (negative target and positive electrode). On the other hand, a clear deterioration of the emission line intensities was observed under conditions of reversed polarity. This negative effect may be attributed to the reduction in electron-ion recombinations due to the stretched plasma plume. The plasma temperature showed a constant value in the average with the increasing electric field in both directions. This effect may be due to the fact that the measured values of Te were averaged over the whole plasma emission volume. The electron density was observed to decrease slightly in the case of forward biasing while no significant effect was noticed in the case of reversed biasing. This slight decrease in Ne can be interpreted in view of the increase in the rate of electron–ion recombinations due to the presence of the electric field. No appreciable effects of the applied electric field on the plasma dynamics were noticed