Se was determined by GF AAS (A SIMAA-6000 graphite furnace
atomic absorption spectrometer; Perkin–Elmer). Solutions were
delivered into the graphite tube by means of an AS-72 autosampler. For sample analyses, a 10-lL volume of a chemical modifier
solution of 5 lg Pd and 3 lg Mg (solutions of 10 g L1 of Pd(NO3)
and Mg(NO3)2, both from Merck) was co-injected into the graphite
furnace with 10 lL of samples or analytical solutions. A Titrisol
standard solution of 1000 mg L1 of Se (Merck) was used to prepare
the reference analytical solutions in 0.14 M HNO3.