graphite furnace AAS
/ GRAF-ite FUR-nis /
Graphite furnace AAS is the high-sensitivity cousin of flame AAS, swapping the open flame for a tiny tube heated like the filament in a toaster. Instead of spraying sample continuously into a flame where most of it escapes, you place one small drop in the tube and zap it with electricity until every last atom of it puffs into the light beam at once.
More precisely, a measured microlitre of sample sits in a small graphite tube. A programmed electric current heats the tube in stages — first to dry, then to char away the matrix (ashing), then a sudden blast to several thousand degrees that atomizes the analyte in a confined puff. The lamp's beam passes through that dense cloud, and the brief absorbance spike is the signal.
It matters because cramming all the atoms into a small space at once gives detection limits far below the flame, reaching parts per billion with just microlitres of sample. The honest trade-offs are slowness — one sample at a time, with a minute-long heating cycle — and a strong tendency to background and matrix interference that demands careful correction.
To measure trace lead in blood, 20 microlitres is pipetted into the graphite tube. The program dries it at 110 C, ashes the organic matrix near 600 C, then fires to about 2000 C; the lead atomizes in a flash and gives a sharp absorbance peak proportional to the lead present.
A drop in a tube, heated in stages, atomized in one burst — sensitivity down to parts per billion.
Graphite furnace AAS is also called electrothermal AAS. The ashing step is meant to burn away the matrix before atomization; matrix modifiers are often added to make the analyte hang on through ashing while the interferences are driven off.