Spettroscopia di assorbimento atomico: interferenza

Atomic absorption spectroscopy encounters three interference categories: spectral, chemical, and physical. Spectral interference occurs when signals from other elements or the flame overlap with the analyte signal, falsely elevating or masking absorbance. Chemical interference results from matrix constituents interacting with the analyte, reducing atomization efficiency. Physical interference arises from non-chemical factors like gas flow rate variations or flame temperature changes affecting the nebulization or atomization process.

Zeeman correction uses a magnetic field to split the absorption line into three polarized components: two sigma (shifted) and one pi (unshifted). By alternating the magnetic field, analyte and background absorbances are measured separately, enhancing accuracy in complex matrices. This method effectively differentiates between the analyte signal and background absorption, reducing spectral interference from overlapping signals.

Smith-Hieftje correction pulses a hollow cathode lamp at high currents, causing the emission line to broaden and undergo self-reversal where the central analytical line diminishes. Absorbance is measured under normal and high-current conditions, allowing differentiation between analyte and background signals. Though it requires only a single light source, the method's sensitivity decreases when self-reversal is insufficient or recovery is too slow.

Ionization interference occurs when the analyte ionizes during analysis, reducing absorption. This can be suppressed by adding an excess of a more easily ionized element, which represses the analyte's ionization through competitive ionization. Additionally, using high atomization temperatures or adding complexing or releasing agents helps prevent the formation of nonvolatile salts that lower atomization efficiency.

Deuterium background correction uses a D2 lamp as a broad-spectrum light source to measure background absorption across a wide wavelength range. A rotating mirror alternates between the hollow cathode lamp and D2 lamp, with the difference between signals isolating analyte absorbance. Though inexpensive and requiring only a single light source, it lacks precision in high-accuracy measurements.

Physical interferences from non-chemical factors like gas flow rate variations or flame temperature changes affect the nebulization or atomization process, causing systematic errors in measurements. These interferences are minimized through frequent calibration, internal standards, sample dilution, or preparing calibration standards with a matrix similar to real samples, which helps compensate for these variations.

Chemical reactions between the analyte and matrix species can form nonvolatile compounds that do not readily atomize, hindering free atom formation for absorption. This interference is avoided by adding a chemical competitor or releasing agent, using very high temperatures to promote atomization, or preparing calibration standards with a sample matrix similar to real samples to compensate for matrix effects.