Briefly 1ml of appropriately dilute
sample was added to a 10ml of volumetric flask
containing 4 ml of distilled water followed by
immediate addition of 0.6 ml of 5% NaNO2, 0.5 ml of
10% AlCl3 after 5 min, and 2 ml of 1 M NaOH after 1
min. Furthermore, each reaction flask was then
immediately diluted with 2.4 ml of distilled water and
mixed.