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.
In atomic absorption measurements, solid samples are dissolved in a suitable solvent to form a clear solution before atomization.
Insoluble samples are digested with hot mineral acids, either on a hot plate or through microwave heating.
Other methods to obtain clear solutions include oxidizing the sample with liquid reagents, combusting it in closed containers, or fusing it with reagents at high temperatures.
Using low-molecular-weight organic solvents improves nebulizer efficiency and absorbance levels, while extraction from aqueous solutions into water-immiscible solvents reduces matrix interferences.
Calibration curves using multiple standard solutions bracketing the analyte concentration are necessary to determine the linear absorbance–concentration relationship within that concentration range.
The standard-addition method, where one sample portion is spiked with a standard solution, is used to identify and minimize matrix interferences.
Typical detection limits in AAS vary depending on the atomization technique: between 1 and 20 ng/mL for flame atomization, and ranging from 2 to 10 pg/mL for electrothermal atomization.
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