Atomic Absorption Spectroscopy (AAS) was developed by CSIRO Scientist Dr Alan Walsh in the 1950s.
Light with specific frequencies is absorbed by different metals when they vaporize in a flame.
The energy absorbed excites electrons, moving them from their ground state to a higher energy state.
Atomic Absorption Spectroscopy uses hollow cathode lamps to emit light with these frequencies which is then absorbed by the sample containing the metal ion.
The amount of light absorbed is proportional to the concentration of the metal ion in solution.
Concentrations are often expressed as mg/L or ppm.
The amount of light absorbed by the sample is compared to the amount of light absorbed by a set of standards of known concentration.
Atomic Absorption Spectroscopy can be used to measure the concentration of metals in :
mining operations and in the production of alloys as a test for purity
contaminated water, especially heavy metal contamination in industrial waste water
organisms, such as mercury in fish
air, eg lead
Example : Undiluted Sample
Atomic Absorption Spectroscopy (AAS) can be used to determine the lead concentration in soil collected from the side of a road.
A student prepared standard lead solutions for comparison and the aborbance of each solution was measured.
A road-side soil sample was also prepared.
The results are shown in the table below.
What was the concentration of lead in the soil sample?
Step 1: Draw a calibration curve using the data:
Plot the calibration curve using the concentrations and absorbances of the standard solutions (shown as red x's on the graph)
Draw a line of best fit through the plotted points (shown as a red line on the graph)
Step 2: Use the calibration curve to find the concentration of lead in the sample:
Mark the position of the 0.58 absorbance of the sample being investigated (shown on the graph as a blue x)
(Draw a horizontal line, parallel to the x axis, from absorbance 0.58 until it meets the line drawn on the graph. Shown on the graph as a dotted blue line.)
Read off the concentration of lead in the sample from the graph, 3.50 ppm
(From the blue x on the line in the graph, draw a line vertically down to meet the x axis. Shown on the graph as a dotted blue line.)
The concentration of lead in the sample was 3.50 ppm.
(Check that your answer is sensible. The absorbance of the sample lies between the absorbance for standards 3 and 4, therefore the concentration of lead in the sample must be between 3.00 and 4.00 ppm)