After cooling to room temperature, 5 ml of 3 M HCl was added
to each crucible and placed on a sand bath at 120 ◦C for 3–4 h for
dryness. Subsequently, crucibles were removed from the sand bath
and 10 ml of 1 M HNO3 was added to dissolve the ash. After stirring,
the solution was transferred to a 50 ml volumetric flask and make
volume up to the mark with double-deionized water. The samples
were then filtered into 50 ml tubes and kept at 4 ◦C until analysis.
The samples were analyzed for Na and K contents using Atomic
Absorption Spectrometer (Perkin-Elmer 3300, Norwalk, CT, USA).