Microwave-assisted digestion using diluted HNO3 and H2O2 for macro and microelements determination in guarana samples by ICP OES

Abstract

A microwave-assisted digestion procedure using diluted HNO₃ and H₂O₂ was developed for multi-element determination in guarana samples by ICP OES. Optimization step was performed employing a mixture design with pseudocomponents using HNO₃, H₂O₂ and H₂O. The analytical signal of each element, residual acidity and residual carbon content were optimized simultaneously using the desirability function. The best condition for digestion of a 250 mg sample mass resulted from a mixture constituted by 1.0 mL of HNO₃, 3.0 mL of H₂O₂ and 6.0 mL of H₂O. This condition allowed final digests with residual acidity and residual carbon content of 0.4 mol L^-1 and 6.5%, respectively. The method was validated and applied for the determination of K, Ca, Mg, S, P, Cu, Fe, Mn and Zn in 72 guarana seed samples from Bahia state. This work presents unpublished results about the mineral composition of guarana seed samples produced in Bahia state, Brazil.

Keywords: Diluted nitric acid; Guarana; Macro and microelements; Microwave-assisted digestion; Mixture design.