Geological samples were collected from different
regions in Venezuela. In this study we used three
common soil types: clay from Corozo (0-10 cm) and
Camaguan (0-10 cm), sand-clay-loam from Cunaviche
(0-7 cm) and stream deposits from San Fernando
(0-10 cm). After collection, each wet soil
sample was mixed thoroughly and separately and a
portion was oven-dried at 80°C for 6 h. For the digestion
process and slurry analysis, approximately 3
g of the sample were homogenized in a porcelain
mortar, then ground in a mill, which was cleaned between
samples by grinding a small amount of quartz
and washing thoroughly with distilled and deionized
water, and then dried. In order to eliminate any possible
contamination coming from the cleaning procedure,
small amounts of each sample were ground before
the grinding step.