Graphite Furnace Atomic Absorption spectroscopy (GFAA) is a sensitive analytical method suitable for the routine measurement of trace elements. Very briefly, in a GFAA instrument, the sample is injected into a graphite tube that is heated so that solvents and matrix components evaporate, and the remaining analyte is atomized. The graphite furnace is an electrothermal atomizer system that can produce temperatures as high as 3,000°C. It provides the thermal energy to break chemical bonds within the sample and produce free ground-state atoms. Ground-state atoms are capable of absorbing energy, in the form of light, and are elevated to an excited state. A light source (e.g., hollow cathode lamp) emits light at a specific wavelength and the emission spectrum passes through the graphite tube containing the remaining atomized analyte. The analyte absorbs light at the specific wavelength and light that has not been absorbed will reach the detector after first passing trough a monochromator. This is illustrated in Figure 1.
Figure 1: The atomic absorption process
Light with initial intensity, Io, is focused on the sample cell (furnace) containing ground state atoms. The initial light intensity is decreased by an amount proportional to the concentration of analyte atoms in the cell. The light is then directed onto the detector where the reduced intensity, I, is measured. The amount of light absorbed is determined by comparing I to Io, and this is related to the concentration of the analyte present in the sample.
Routine GFAA analyses at µg/L level for most elements have made GFAA the regular method for trace metal analysis applications. A number of methods for the analysis of metals in environmental samples are based on GFAA. In clinical analysis, it is used in analyzing metals in biological fluids such as blood and urine. In some pharmaceutical manufacturing processes, trace amounts of a metal catalyst used in the process are sometimes present in the final product. GFAA is used to determine the amount of catalyst present in that final product. In industrial materials, GFAA is used to check that the major elements are present and that toxic impurities are lower than specified.
Advances in instrumentation and techniques have made it possible to analyze very complex sample matrices, such as those frequently found in biological and geological samples. The small sample volume requirement (µL range) offers additional benefits where the amount of sample available for analysis is limited, as in many clinical analyses.