Multi-energy calibration as a strategy for elemental analysis of fertilizers by microwave-induced plasma optical emission spectrometry

Multi-energy calibration (MEC) was applied for the determination of As, Ba, Cd, Cr, and Pb in fertilizer samples by microwave-induced plasma optical emission spectrometry. Commercial fertilizer samples and a certified reference material of mineral fertilizer (CRM NIST 695) were digested using microwave-assisted acid. The MEC approach was carried out using only two calibration solutions: S-1, composed of 50% v/v digested sample and 50% v/v standard reference solution containing the analytes, and S-2, composed of 50% v/v sample and 50% v/v blank solution. The accuracy of the method was evaluated by analyzing CRM NIST 695, with recoveries in the 96-101% range. Addition and recovery experiments were also carried out for Cd determination, with recoveries between 92 and 105% for the evaluated samples. The MEC strategy was compared with traditional external standard calibration and standard additions methods and was the only one to provide accurate results for all evaluated analytes.