Preparation of standard stock solutions
168 mg of the pigment (3, 3
1
,4
1
,5,7-Pentahydroxflavylium chloride)
was dissolved in 20 ml analytical grade methanol in a 100 ml flask
and the solution made up to mark with methanol to give 5 mM
solution. 5 mM solution in ethanol was similarly prepared.
135 mg of Pb (NO3)2, 86 mg of CdCO3 and 134 mg of CrCl3 were
each dissolved in 20 ml of distilled water in separate 100 ml flasks.
The solutions were made up to the mark with distilled water to 5 mM
solutions of the salts. Buffer solutions for pH range of 1 – 8 were
prepared as described by Lange (1973).