Standard solution of copper, cadmium, potassium, calcium, magnesium (1000 μg/mL) and nitric acid (AR grade)
were purchased from Thermo Scientific, UK. Hallow cathode lamps of copper, manganese, mercury, potassium,
calcium, magnesium and cadmium were parts of AAS as purchased from PG-Instruments, UK. Grade 1 quality
water (0.01 μS/cm) was prepared in our own laboratory