BIOL 380
Tom Huff, Instructor
thuff@gmu.edu

In atomic absorption, there are two methods of adding thermal energy to a sample. A graphite furnace AAS uses a graphite tube with a strong electric current to heat the sample. In flame AAS, we aspirate a sample into a flame using a nebulizer. The fl ame is lined up in a beam of light of the appropriate wavelength. The flame (thermal energy) causes the atom to undergo a transition from the ground state to the first excited state. When the atoms make their transition, they absorb some of the light from the beam. The more concentrated the solution, the more light energy is absorbed!

The light beam is generated by a lamp that is specific for a target metal. The lamp must be perfectly aligned so the beam crosses the hottest part of the flame and travels into the detector. The detector the measures the intensity of the beam of ligh t. When some of the light is absorbed by a metal, the beam's intensity is reduced. The detector records that reduction as an absorption. That absorption is shown on a readout by the data system. The figure above shows the schematic diagram of a flame AAS. As the diagram indicates, there are four primary parts to the system--the light source, the flame apparatus, the detector, and the data system.

Fortunately, we do not need to separate solutions containing different metals. No chromatography is required for this instrument. We merely change lamps and adjust the detector wavelength.

We can find the concentrations of metals in a sample running a series of calibration standards through the instrument. The instrument will record the absorption generated by a given concentration. By plotting the absorption versus the concentrations of the standards, a calibration curve can be plotted. We can then look at the absorption for a sample solution and use the calibration curves to determine the concentration in that

Link to Instrument Operation

Last update: February 18, 1998