An environmental chemist working for the Environmental Protection Agency (EPA) w
ID: 981824 • Letter: A
Question
An environmental chemist working for the Environmental Protection Agency (EPA) was directed to collect razor clams from a heavily-contaminated river superfund site and analyze them for cadmium (Cd^2" ) content using graphite furnace atomic absorption spectrometry (GFAAS) The chemist dried the dams at 95 C overnight and ground them in a scientific blender, resulting in ~ 50 g of homogenized dry weight .A representative 81.00 mg sample was taken from the ~ 50 g of dry material and dissolved in 100.00 mL of 0. 7 M HQ to create a sample solution. Using the method of standard additions. The chemist prepared rive standard solutions in 100.00-ml volumetric tasks. Each containing 5 00-mL aliquots of the sample solution Varying amounts of a 96 0 ppb (Mu g . L ^-1 ) cadmium standard were added to each of the flasks, which were then brought to volume with 0.1 M HCI The solutions wore then examined for their Cd^2' content using GFAAS. resulting m the following absorbance data Determine the amount of Cd^2" per gram of dry dam Express your final result as milligrams of Cd^2" per gram Of dry clamExplanation / Answer
Answer:
81 mg of dried cadmium sample were dissolved in 100ml of 0.1M HCL. 5 ml from this standard solution were added to 100ml volumetric flask and varying amount of 96 ppb (ug/L) cadmium standard were added to each flask and volume make up with 0.1N HCL at last. And absorbance data for those 5 solutions is given in the question
In graph we have ploted line intercepts x axis at - 0.442 approx
i.e 0.442 ug/L
0.442/L ×0.1 L = x ×0.005L
X = 8.84/L
Suppose no volume changed during 81 mg is mixed with 0.1 L HCL
8.84 ug/L × 0.1L = 0.884 ug
[0.884 ug of Cd/ 81 mg dry Cd] × [1000mg dry Cd/1 g dry Cd] × [1mg Cd/1000 ug Cd] = 0.0109 mg/gm of dried sample
0.0109 mg of Cd is present in per 1 g of dried sample
Since dried sample is 50g , 50 gm will contains = 0.5456 mg of Cd