We used an atomic absorption spectrophotometer
model AA6 (Varian Tectron, Melbourne, Australia)
with a carbon rod CRA 90. The temperature of the
carbon rod is measured and controlled with a resistance
feedback system, a standard feature of the CRA 90, to
keep the temperature constant during the ashing and
atomization steps. We used a cadmium hollow-cathode
lamp (Varian) and a hydrogen continuum lamp for
measuring the nonselective absorption.