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 (Cd2 ) content using graphite furnace atomic absorption spectrometry (GFAAS). The chemist dried the clams at 95° C overnight and ground them in a scientific blender, resulting in ~ 50 g of homogenized dry weight. A representative 64.00 mg sample was taken from the ~ 50 g of dry material and dissolved in 100.00 mL of 0.1 M HCl to create a sample solution. Using the method of standard additions, the chemist prepared five standard solutions in 100.00-mL volumetric flasks, each containing 5.00-mL aliquots of the sample solution. Varying amounts of a 89.0 ppb (μg ·L-1) cadmium standard were added to each of the flasks, which were then brought to volume with 0.1 M HCl. The solutions were then examined for their Cd2 content using GFAAS, resulting in the following absorbance data.

Determine the amount of Cd2 per gram of dry clam. Express your final result as milligrams of Cd2 per gram of dry clam

	Sample 5	cd2+ standard volume 0	absorbance 0.080
	5	2.50	0.119
	5	5	0.163
	5	7.50	0.200
	5	10	0.241

Answer 1

According to the experiment the cadmium standard concentration is

The concentration need to be measured for the soluions prepared in 100 mL flasks.

Therefore the standard volumes used with sample has concentration

And the absorbance of this standard solution= Absorbance of standard with sample - absorbance of only sample

Absorbance of sample = 0.080

The calibration is linear and the slope is

The absorbance of the sample is = 0.080 A.

Therefore the concentration of the sample=

In the 5 mL sample aliquot Cd2+ conc.

64 mg sample is dissolved in 100mL of sample solution

64 mg sample has Cd2+ concentration =

sample contains =

samples contains

Therefore the 1 gram of dry clam has 0.138 mg Cd2+.