An aliquot (250 lL) of each extract or
standard solution was mixed with 1.25 mL of dd H2O and 75 lL of
5% NaNO2 solution. After 6 min, 150 lL of 10% AlCl3.H2O solution
were added. After 5 min, 0.5 mL of 1 M NaOH solution were added
and then the total volume was made up to 2.5 mL with distilled
H2O)