Elements Ca, Cu, Fe, Mg and Zn were estimated following the
method of Bhargava and Raghupathi (1993) using diacid mixture
method. In 1 g powdered unpolished rice sample, 10 ml
HNO3:HClO4 acid mixture (9:4) was added and mixed by swirling.
The mixture was placed in a digestion chamber and heated at
higher temperature until fuming of red nitrogen dioxide ceased.
The contents were evaporated to reduce the volume to 3–5 ml.
The completion of digestion was confirmed by the formation of
colorless liquid. After cooling, 20 ml of de-ionized water was added
and the solution was filtered through Whatman filter paper 1. The
aliquots of this solution were used for determination of mineral
elements. Individual standard stock solutions (1 mg/L) for each
mineral element were prepared for quantification. Different
dilutions ranging from low to high concentrations were made
and standard graph was plotted.