An Optima 4300 DV inductively coupled plasma optical emission
spectrometer (PerkinElmer, USA) with axial view configuration was
used for Cu and Fe determination. A GemCone™ nebulizer coupled to
a cyclonic spray chamber was used. Copper and Fe were determined
at 324.752 and 238.204 nm, respectively. The radiofrequency power
was set at 1400 W and argon (99.996%, White Martins, São Paulo,
Brazil) was used for plasma generation. Plasma gas flow rates were set
at 15, 0.2, and 0.70 L min−1 for principal, auxiliary and nebulizer gas,
respectively. The operational parameterswere selected as recommended
by instrument manufacturer.