0.1 g of standard reference material (SRM)
(GBW 07309) was digested with aqua regia (12
ml concentrated hydrochloric acid and 4 ml of
concentrated nitric acid) at room temperature then
it was heated to 95 8C. After the evaluation of
NO2 fumes had ceased, the mixture was evapo-
rated almost to dryness on a sand-bath and mixed
with 8 ml of aqua regia. Then the mixture was
again evaporated to dryness. After evaporation 8/
9 ml of distilled was added and the sample was
mixed. The resulting mixture was filtered through
a blue band filter paper. The filtrate was diluted to
10 ml with distilled water