Background: Reliable analytical methods for metals determination in tea is a demand of the
nutritional and toxicological sciences. In this work, a constrained mixture design has been applied to
develop an efficient closed-vessel microwave-assisted digestion procedure for Ca, Cu, Fe, K, Mg, Mn,
Na, Sr and Zn determination in vegetal leaves used for tea preparation.
Methods: The optimization step was carried out using a constrained mixture design to find digested
samples of good characteristics such as clarity, low residual carbon and low final acidity. The studied
metals and residual carbon were determined by simultaneous inductively coupled plasma optical emission
spectrometry (ICP OES).
Results: The optimum proportions found by applying the mixture design were 31.3, 56.2 and 12.5%
(v/v) for H2
, respectively. The accuracy of the method was confirmed by analysis of
two certified reference materials: apple leaves (NIST 1515) and spinach leaves (NIST 1570a). The proposed
method was applied for the determination of studied metals in vegetal leaves used for the preparation
Conclusion: The developed method has presented adequate analytical characteristics to determining of
studied elements from tea samples with quickly, accuracy, precision and reliability.