RESUMO
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 250â¯mg sample mass resulted from a mixture constituted by 1.0â¯mL of HNO3, 3.0â¯mL of H2O2 and 6.0â¯mL of H2O. This condition allowed final digests with residual acidity and residual carbon content of 0.4â¯molâ¯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 This work presents unpublished results about the mineral composition of guarana seed samples produced in Bahia state, Brazil.