Determination of elements in agricultural soils using IR laser ablation inductively coupled plasma atomic emission spectrometry

Direct sampling of soil samples was studied using laser ablation inductively coupled plasma atomic emission spectrometry (LA-ICP-AES). Samples were pressed into pellets together with a binder and an internal standard. The amount of ablated material for pellets with various binding materials was evaluated. Silver and aluminium powders were found as adequate binders for the pellet preparation. Optimisation of laser parameters, and sample displacement during interaction have been performed. Moderate laser pulse energy of 150 mJ together with a 20-Hz repetition rate was found to be the most suitable to obtain stable analytical signal. Sample displacement leads to more precise sampling and long time signal plateau that can be measured even with sequential spectrometers. Precision was approximately 5% for most of the elements studied. Calibration was performed using soil samples spiked with solutions. Internal standards improved correlation coefficients for calibration, which were at least 0.98. Germanium powder was the most efficient internal standard. Certified reference soils were analysed with an accuracy better than 10%.