A flame atomic absorption spectrometer (model AAS vario 6,
Analytik Jena, Germany) equipped with a deuterium background correction
and an air/acetylene flame was used. The hollow cathode
lamps of Cu and of Fe were operated at 3 and 8 mA, wavelength set at
324.8 and 248.3 nm and spectral band pass set at 1.2 and 0.2 nm,
respectively. Signals were obtained as integrated absorbance and analytical
signal was integrated within 15 s.