Assessing the greenness of optimized ultrasound and infrared assisted extraction through analytical metrics

Sample preparation involves a critical step due to the high organic matter content that implies its decomposition, prior to analysis. Two alternative analytical strategies for sample preparation employing diluted HNO₃ were optimized and compared, assisted by ultrasound (USAE) and infrared (IRAE) radiation. Multielement determination was achieved by MIP OES. For optimization of experimental conditions, a central composite design centered on the faces was carried out, considering four and five factors for IRAE and USAE, respectively. Dissolved organic carbon (DOC), residual acidity (RA) and solid residue (SR), significantly influence the responses to be evaluated. The response surface methodology was implemented to find the best combination of mass, diluted reagents (HNO₃ and H₂O₂), time and temperature in order to minimize responses for elemental extraction in animal feed samples. The optimized experimental conditions: 500 mg of sample mass, 60 °C of bath temperature, 30 min of extraction time, 2 mol L⁻¹ HNO₃ and 27% H₂O₂, were used to validate the USAE procedure. The conditions established for IRAE were 500 mg of the swine feed sample, followed by the addition of 2 mL of 2 mol L⁻¹ HNO₃ and 23% H₂O₂, irradiating for 23 min. Recoveries ranged from 81 to 114%, with good precision (RSD < 4%). Using five index tools the greenness of the proposed methods was demonstrated. According to IRAE simplicity, reliability, fast and easy to implement, it was successfully applied to the determination of Ca, Cu, Fe, K, Mg, Mn, P and Zn in agrifood samples.