Atomic absorption spectroscopy (AAS) determines the presence of metals in liquid samples. Metals include Fe, Cu, Al, Pb, Ca, Zn, Cd and many more. It also measures the concentrations of metals in the samples. Typical concentrations range in the low mg/L range.
In their elemental form, metals will absorb ultraviolet light when they are excited by heat. Each metal has a characteristic wavelength that will be absorbed. The AAS instrument looks for a particular metal by focusing a beam of uv light at a specific wavelength through a flame and into a detector. The sample of interest is aspirated into the flame. If that metal is present in the sample, it will absorb some of the light, thus reducing its intensity. The instrument measures the change in intensity. A computer data system converts the change in intensity into an absorbance.
As concentration goes up, absorbance goes up. The researcher can construct a calibration curve by running standards of various concentrations on the AAS and observing the absorbances. In this lab, the computer data system will draw the curve for you! Then samples can be tested and measured against this curve.
It is important to understand the theory behind any instrument if you are to be successful using that instrument. However, AAS theory can be looked at either on a simplified basis or a complex basis. Try looking at the complex first--you may surprise yourself by understanding it!
Look over the following sections before the lab on Wednesday. If you do not understand the background section, go on to the other sections. We will have a chance to review the background in the lab prior to the experiment. You should understand the instrument's set-up and operation prior to lab.
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