An environmental chemist working for the Environmental Protection Agency (EPA) w
ID: 486561 • 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 their Cd^2+ content using graphite furnace atomic absorption spectrometry (GFAAS). The chemist dried the clams at 95 degree C overnight and ground them in a scientific blender, resulting in approximately 50 g of homogenized dry weight. A representative 57.27 mg sample was taken from the approximately 50 g of dry material and dissolved in 100.0 mL of 0.1 M HCI to create a sample solution. Using the method of standard additions, the chemist prepared five standard solutions in 100.0-mL volumetric flasks, each containing 5.00-mL aliquots of the sample solution. Varying amounts of a 79.0 ppb (mu g/L) Cd^2+ standard were added to each of the flasks, which were then brought to volume with 0.1 M HCI. The Cd^2+ content of the solutions was then analyzed using GFAAS, resulting in the following absorbance data. Determine the amount of Cd^2+ per gram of dry clam. Express your final result as milligrams of Cd^2+ per gram of dry clam.Explanation / Answer
Amount of dry clam taken: 57.27 mg
Let's assume this dry clam contains 'x' mg of Cd+2
Now we have added 79.0 ppb (micron/litre) of Cd+2 standard sample.
If we observe the first two data sets obtained from GFAAS, first data set has the value 0.00 which is the amount of Cd+2 contained in the clad intself ( which we have assumed to be x mg)
In data set 2, the amount of Cd+2 is : 0.079*2.5*5= 0.9875 microgram.
Now the absorbance data is directly proportional to the concentration. Hence the equation can be formed as x/(x+0.000987.5)= 0.08/0.119
imples => x = 6.64e-4 mg
Thus the amount of Cd+2 is 6.64e-4 mg in 57.27 mg of clam.
1 gm of clam contain: 0.0116 mg of Cd+2
Final Result: 0.0116mg Cd+2/ g clam