Solutions of 0.01M NaOH and HCl (from Aldrich) were used for
pH adjustment. Cr(VI) stock solution (from Merck) was prepared
from potassium salts of dichromate (K2Cr2O7), which is analytical
grade. Solutions were stored in plastic sealed beaker. A series
of standard metal solution were prepared by appropriate dilution
of the stock metal solution. Dissolved Cr(VI) ions in the samples
at least three concentrations of each were determined from linear
graph of calibration curve.