2.2. Chemical reagents
Standard solutions of Se, Cu, Cr, and Mn (1000 ± 0.002 mg/l)
(Tritisol, Merck, Darmstadt, Germany) were used and diluted as
necessary to obtain working standards with acidified water with
0.2% nitric acid. High-quality concentrated nitric acid (65%) and
perchloric acid (65%) were used for sample mineralization.
Hydrochloric acid (37%) was used to reduce the Se+6 to Se+4 in samples
after mineralization for Se determination. Sodium borohydride
and sodium hydroxide were employed for hydride
generation. Magnesium nitrate was used to prepare the matrix
modifier for Cu and Cr determinations. All solutions were prepared
from analytical reagent-grade chemicals (Suprapur, Merck,
Germany