Study of matrix effects in laser induced breakdown spectroscopy on metallic samples using plasma characterization by emission spectroscopy

Characterization techniques based on emission spectroscopy are used to investigate matrix effects in laser induced plasmas obtained from metallic samples with Ni, Cu and Al matrices. An infrared Nd:YAG laser is used to generate the plasmas in air at atmospheric pressure. The plasma emission is detected at the time window 3–4 µs. Combining the Boltzmann plot, Stark shift, and curve-of-growth (COG) methods, a set of four parameters (T, Ne, Nl, βA) is determined for each matrix that provides a complete description of the plasma emission, assuming the model of a homogeneous plasma in local thermodynamic equilibrium. For the COG measurements, a total of 28 metallic samples were prepared with varying concentrations of an element, selected to form a binary sample with the matrix element. The results reveal the existence of a weak matrix effect that leads to a variation of the plasma parameters. The smallest variation is obtained for the temperature, which is higher in about 500 K (4%) for the Cu matrix. The greatest electron density (20% variation) and Nl (50% variation) correspond to the Al sample. However, the line intensity for a given atomic concentration in the sample is only slightly different for the three matrices due to a compensation of the effects produced by the variation of the plasma parameters. This compensation is interpreted to result from a different influence of plasma shielding taking place for each matrix.