14.8 : Atomic Absorption Spectroscopy: Lab

For AAS measurements, samples must be introduced as clear solutions, often requiring extensive preliminary treatment to dissolve materials like soils, animal tissues, and minerals. Common methods for sample preparation include treatment with hot mineral acids, wet ashing, combustion in closed containers, high-temperature ashing, or fusion with reagents.

Solutions containing organic solvents, such as low-molecular-mass alcohols, esters, or ketones, enhance absorbances by increasing nebulizer efficiency and promoting rapid solvent evaporation. Using immiscible solvents like methyl isobutyl ketone can extract chelates of metallic ions, improving sensitivity and reducing interferences from matrix components.

Calibration is crucial in AAS since absorbance versus concentration plots are often nonlinear. Periodic calibration curves and the use of standard solutions bracketing the analyte concentration are necessary for accurate analysis. The standard-addition method is commonly used to compensate for chemical and spectral interferences caused by the sample matrix.

It's important to note that detection limits in AAS vary based on the atomization technique. Flame atomization has detection limits ranging from 1 to 20 ng/mL, while electrothermal atomization has detection limits between 0.002 to 0.01 ng/mL. Flame atomic absorption analysis typically has a relative error of a few percent, which can be reduced with special precautions. Errors in electrothermal atomization are usually 5 to 10 times higher than those in flame atomization.