2.2. Sample digestion procedures
To ensure the removal of organic impurities from the samples
and thus prevent the interference in analysis, the sampleswere digested with concentrated Nitric acid. 5 mL of conc.
HNO3 was added to 100 mL of sampling water into the 250 mL
conical flask then heated on a hot plate and evaporated till
20 mL was left. After cooling the flask again 5 mL of conc.
HNO3 was added and heated the flask on the hot plate. The
digestion was continued till 10 mL was left and finally filtered
and diluted with distilled water into 100 mL of volumetric
flask and stored in the refrigerator.