Atomic Absorption Spectroscopy

Flame AAS nebulizes the sample into a hot flame (typically 2000–2700°C), suitable for moderate to high concentrations. Graphite furnace AAS heats a small sample volume to very high temperatures (~2800°C) in a graphite tube, allowing smaller injection volumes and providing 100–1000 times better detection limits. Graphite furnace is preferred for trace analysis but is slower and requires more careful optimization.

The hollow cathode lamp emits sharp, element-specific resonance lines at the exact wavelengths absorbed by ground-state atoms of that element. This ensures maximum sensitivity and selectivity. Broadband light sources (like xenon lamps) do not work well because they lack sufficient intensity at the narrow absorption lines and cannot distinguish between similar elements.

Background absorption from smoke, dust, or nearby absorption lines is corrected using either a deuterium lamp (which emits continuous UV light) or the Zeeman effect (applying a magnetic field to shift sample absorption away from background). The corrected absorbance is obtained by subtracting the background signal from the total signal.

Chemical interferences occur when sample components form refractory compounds (like oxides or phosphates) with the analyte, preventing complete atomization and suppressing the measured signal. Solutions include adjusting flame temperature, adding releasing agents (calcium chloride or lanthanum) to prevent analyte binding, or using the standard addition method to compensate for matrix effects.

Standard AAS measures one element per analysis because it uses an element-specific hollow cathode lamp and wavelength. However, sequential or simultaneous multi-element systems with multiple lamps and optics exist but are more complex and expensive. For routine multi-element analysis, ICP-OES or ICP-MS are more practical alternatives.