complex may not be stable in water. The exact cause of
the results still needs further investigation, and the reason
for the decreased absorbance is unknown. In acetate buffer
solutionpH4.8 (Fig. 2 (b), both Fe (II) and (III) can form complexes
with a chemical or chemicals in the guava leaf extract.
Both Fe (II) and (III) complexes show maximum absorption
at 570±20 nm. The blank solution, guava leaf extract, did
not show any significant absorption in the visible region. In
a medium of diluted HCl pH 4.8, maximum absorption at
570±20 nm was observed (not shown) only at high Fe (III)
concentration but at much lower value as compared to the one
in acetate buffer of the same pH. This indicates that guava leaf
extract–iron complexes can only be formed at a suitable pH
and that the use of buffer solution to control pH is necessary.