with one modification in that the extraction reagent for the
exchangeable fraction was changed to 1.0 M NH4OAc
instead of 1.0 M MgCl2 at pH 7.0 because of the lower
matrix effect posed by the former reagent in the AAS
analysis. About 5 g of sand samples in triplicates were
weighed accurately and put through the extraction stages in
50 ml polycarbonate centrifuge tubes with screw-on caps.
The extract was separated from the sand by centrifuging at
2000 rpm for 15 min and stored in polyethylene sample
bottle before analysis. The residue was washed with deionized
water before a new extraction stage.