Espectroscopia de Absorção Atômica: Laboratório

Atomic absorption measurements require clear solutions for accurate analysis. Solid samples must be dissolved in suitable solvents or digested with hot mineral acids on a hot plate or through microwave heating. Other methods include oxidizing samples with liquid reagents, combusting them in closed containers, or fusing them with reagents at high temperatures to obtain clear solutions suitable for atomization.

Low-molecular-weight organic solvents like alcohols, esters, and ketones enhance absorbance by improving nebulizer efficiency and promoting rapid solvent evaporation. Using immiscible solvents such as methyl isobutyl ketone can extract chelates of metallic ions, improving sensitivity and reducing interferences from matrix components in the sample.

The standard-addition method involves spiking one sample portion with a standard solution to identify and minimize matrix interferences. This technique compensates for chemical and spectral interferences caused by the sample matrix, improving the accuracy of atomic absorption measurements when matrix effects are suspected.

Calibration curves using multiple standard solutions bracketing the analyte concentration establish the linear absorbance-concentration relationship within the measurement range. Since absorbance versus concentration plots are often nonlinear, periodic calibration curves are necessary to ensure accurate determination of analyte concentrations in unknown samples.

Flame atomization has detection limits ranging from 1 to 20 ng/mL, while electrothermal atomization achieves significantly lower detection limits between 0.002 to 0.01 ng/mL. Electrothermal atomization provides superior sensitivity, making it suitable for trace-level analysis of elements requiring lower detection thresholds.

Insoluble samples like soils, animal tissues, and minerals require extensive preliminary treatment. Common methods include treatment with hot mineral acids, wet ashing, combustion in closed containers, high-temperature ashing, or fusion with reagents. These techniques dissolve or convert solid materials into clear solutions suitable for atomic absorption analysis.

Flame atomic absorption analysis typically has a relative error of a few percent, which can be reduced with special precautions. Electrothermal atomization errors are usually 5 to 10 times higher than those in flame atomization, making flame atomization preferable when lower measurement uncertainty is required.