An eco-friendly infrared method for rapid soil sample preparation for multielemental determination by microwave induced plasma atomic emission spectrometry

In order to attain Sustainable Development Goals (SDGs), soils mineral assessment is of great importance, since even small changes in their concentration levels, either due to natural or anthropogenic factors, can affect food security and human health. Sample preparation is a crucial step in the analytical procedure. Considering the refractory nature of soils, conventional digestion procedures are considered a slow stage with high contamination potential. In order to come across to a simplified method for soil sample preparation, an infrared (IR) radiation digester prototype using commercially available IR lamps was evaluated through soil elemental determination by microwave induced plasma atomic emission spectrometry (MIP OES). Soil samples were digested using 2 mL of HNO3 and 2 mL of H2O2, reducing the amount of reagent commonly used. Digestion efficiency was evaluated: dissolved carbon content was < 1% and residual acidity was < 0.08 mol L-1. The proposed procedure allowed Ca, Cd, Cu, Fe, K, Mg, Mn, P, Pb and Zn quantification in soils, with LOQ among 0.4 mg kg(-1) (Mg and Mn) and 172 mg kg(-1) (P). Soil certified reference materials were studied, and determined concentrations were between 80 and 120% compared to certified values. The proposed IR method is straightforward, low-cost, and it is in agreement with green analytical chemistry (GAC) recommendations.