Soil pH was measured on soil suspension using
soil:distilled water at 1:5 (w/v). The mixture of nitric
acid–hydrogen peroxide (2+1, v/v) (for 2.0 g of dried
matter, the mixture of 4.0 ml were used) was added to
2.0 g of soil samples of and dried with occasional shaking
on a hot plate. Then, 2 ml of 1.5 mol l−1 nitric acid
was added to the residue and centrifuged. The clear
solutions were analysed by using direct STAT-FAAS.
A blank digest was carried out in the same way.
The soil extracts were obtained by shaking, separately,
2.0 g of soil samples with 2.0 ml of 0.05 mol l−1
Na2EDTA, 1.0 mol l−1 oxalic acid and concentrated
acetic acid. The mixture was evaporated with occasional
shaking on a hot plate. Then, 2 ml of 1.5 mol l−1
nitric acid was added and centrifuged (this procedure
was mentioned as hot extraction in this text). In addition,
2.0 ml of 0.05 mol l−1 Na2EDTA, 1.0 mol l−1 oxalic
acid, concentrated acetic acid and 1.0 mol l−1 citric
acid were also added to 2.0 g of soil samples at the
room temperature (this procedure was mentioned as
cold extraction in this text). The clear solutions were
analysed by using direct STAT-FAAS. The blank solutions
were carried out in the same ways.