straight from my notes...
3.2.2 Describe the use of atomic absorption spectroscopy (AAS) in detecting concentrations of metal ions in solutions and assess its impact on scientific understanding of the effects of trace elements.
Atomic absorption spectroscopy (AAS) is an important technique in measuring the concentrations of metal ions in very minute quantities. In atomic spectroscopy a liquid sample containing the metal ion to be tested is aspirated through a plastic tube into a flame hot enough to vaporise the molecules into atoms. A cathode lamp of the specific metal passes through the vaporised sample. A detector measures the amount passing through the flame and gives out the absorbance (amount absorbed) reading.
The basis of AAS is the result of the electron structure of the atom. Under quantum theory, electrons move to higher or lower energy levels by absorbing or releasing electromagnetic radiation of a particular frequency. Since each element has a different set of electron energy levels, each has its own set of absorption lines. The greater the concentration of the metal ion, the more radiation is absorbed and the less reaches the detector. According to the Beer-Lambert Law, the amount of light absorbed is proportional to the amount of a substance present. A calibration graph using solutions of known concentrations allows the concentration of the unknown to be determined.
The development of the AAS has allowed chemists to measure accurately and rapidly concentrations of metal ions in water systems and in animals and plants. Such has lead to our understanding of trace elements, those elements which are required by living things in very minute quantities. Prior to this understanding, there were instances where animals had health problems in seemingly good pastureland due to deficiencies in cobalt and human illnesses, due to lack of trace elements in their diet, could not be diagnosed. Now, with atomic absorption spectroscopy, these problems are easily and effectively rectified.
In the University of Sydneys High School Chemistry Workshop, an AAS machine was demonstrated to us and used to test the concentration of Fe2+ ions in various samples of water. The results were as follows:
SOURCE OF WATER, ABSORBANCE, READING CONCENTRATION (PPM)
Tap, 0.003, 0.0
Creek, 0.0012, 0.2
A rusted rainwater tank, 0.252, 4.0
As can be seen, the ability of the AAS technique to measure in parts per million (ppm) allows chemists to measure metal ions of a very low concentration. However, the AAS must be daily calibrated with the ion to be measured for the machine to measure accurately. By monitoring the ions that are known pollutants, atomic absorption spectroscopy is a very effective and inexpensive method to control pollution.
i think some of the info was off Chemistry Contexts, and others were from the sheet given on the day at USYD... but yeah, if you're smart you will reuse the Beer-Lambert law as the chemical principle used for testing water quality at SydneyWater with AAS machines (Monitoring dp 1.2.1).
