In this methods, the sample is completely
oxidized by wet ashing
with concentrated sulfuric acid, concentrated nitric
acid and hydrogen peroxide, or
if only iron and copper are to
be determined, by dry ashing. To determine sulfated residue, the
solution obtained by wet ashing
is transferred to a weighed
dish, evaporated to dryness, ignited at 775 degree C, cooled and weighed. In determining lead, iron and copper, the
solution resulting from the
wet ashing is mixed with
alcohol and filtered to give
a precipitate of
primarily and sulfate. This precipitate
is boiled with
sodium carbonate and then precipitated
with hydrogen sulfide.
Iron and copper are determined on
separate aliquots of the
filtrate from wet
ashing. The iron is separated
as the hydroxide and determined colorimetrically as the
orange ferrous orthophenanthroline complex,
while copper is
determined colorimetrically as the
yellow diethyldithiocarbamate
complex
