Question

Imported ceramic bowls are analyzed for toxic heavy metals such as cadmium since these metals can be leached from the ceramic by the food in contact with it. The amount of cadmium that can be leached from the bowl is determined by adding an acetic acid solution to the bowl for a 24 hour period, after which the cadmium concentration in the acidic leaching solution is determined. In one experiment, the cadmium concentration in an acidic leaching solution was analyzed using inductively coupled plasma atomic emission spectroscopy (ICP-AES). A series of cadmium standards were prepared from a 100 ppm Cd stock solution. A micropipet was used to deliver 0.10 mL, 0.20 mL, 0.30 mL, 0.40 mL, 0.50 mL, and 0.60 mL of the stock solution to six separate 50.0 mL volumetric flasks. A known, constant amount of a yttrium stock solution was added as an internal standard, resulting in a final concentration of 0.80 ppm Y in each flask. The volumetric flasks were then diluted to the mark. 25.0 mL of the leaching solution was then pipetted into a separate 50.0 mL volumetric flask. The same known, constant amount of the yttrium stock solution was added to the flask containing the leaching solution, again resulting in a final concentration of 0.80 ppm Y. The flask was then diluted to the mark. The intensities of the cadmium and yttrium emissions are shown in the table below for each of the standard solutions and the unknown solution. Calculate the cadmium concentration in the original leaching solution.

Answer 1

Amount of Emission is directly related to concentration of the Cadmium in the solution [Beer lambert's law]

Since there is a direct relationship, we plot the volume versus emission values and try to ensure drawing a straight line covering maximum points and once the straight line is obtained, we draw a perpendicular starting from the emission value of unknown on y-axis onto the graph line and from the intersection point further drop a perpendicular onto x-axis which intersects at 0.37 ml.

So the volume of unknown Cd solution would be 0.37 ml

100 ppm stock solution of 1 litre [1000 ml] is given to us

0.37 ml * 100 ppm = 0.037 ppm

1 1000 ml

so unknown solution has 0.037 ppm