Investigation of matrix effect on dry inductively coupled plasma conditions using laser ablation sampling

The sample matrix can influence the temperature, electron number density, and other excitation characteristics in the inductively coupled plasma (ICP). These ICP characteristics were investigated by measurements of the ionic to atomic spectral line intensity ratio of a test element (e.g. Mg and Zn). The effect of matrices of calcium (CaCO₃ and CaF₂), strontium (SrCO₃), lithium (Li₂O, Li₂CO₃ and LiF), magnesium (pure Mg and MgO), and aluminium metal on plasma conditions was studied using laser ablation sampling. Two Nd:YAG lasers were used to ablate the test element and the matrix simultaneously. Different amounts of matrix were ablated by varying one laser irradiance; the laser irradiance for the ablation of the test element was kept constant. Strontium, calcium, and magnesium had a more pronounced matrix effect than the easily ionizable elements (Li, Na and K). The matrix effect was independent of the anion. Experimental results suggest that the matrix effects may be due to a mechanism that involves the second ionization level of the elements (Sr, Ca and Mg).