Microwave-assisted digestion for multi-elemental determination in beans, basil, and mint by ICP OES and flame...

A microwave-assisted digestion method using diluted HNO₃ was proposed for subsequent determination of Ca, Cd, Co, Cu, K, Mg, Mn, Mo, Na, P, Pb, S, V, and Zn in beans, basil, and mint using ICP OES and flame photometry. After applying factorial design, the optimized conditions were an HNO₃ concentration of 1 mol L^-1, 2.5 mL of H₂O₂, and a digestion time of 20 min. The method accuracy was assessed using seven reference materials, with statistical agreement between determined and certified values and an RSD of up to 11 %. Linearity was satisfactory (r > 0.999), and limits of quantification ranged from 0.031 mg kg^-1 (Mn by ICP OES) to 60 mg kg^-1 (K and Na by flame photometry). Applying the method to real samples, the concentrations obtained met the Cd limits established by international regulations. Finally, low agreement was verified between measured concentrations and those reported on food packaging.