Spettroscopia di emissione atomica: interferenze

Atomic emission spectroscopy experiences two main interference types: spectral and chemical. Spectral interferences arise from overlapping emission lines or bands produced by high-temperature atomizers that excite a wide range of elements and generate complex emissions from oxides, hydroxides, and combustion products. Chemical interferences occur when analytes react with other species to form stable compounds that do not dissociate, altering analyte signals.

High-temperature plasma sources contain abundant electrons that offset ionization interference. Fewer species remain stable in plasma conditions, reducing interference from inorganic anions, organic solvents, and dissolved species. Additionally, introducing easily ionizable elements into samples and standards counteracts chemical interferences and improves sensitivity by promoting analyte ionization.

Four main strategies reduce spectral interferences: increasing instrument resolution to separate overlapping lines, choosing alternative emission lines less prone to overlap, optimally placing the detector in low-background regions, and applying background correction techniques. These approaches address the complex emissions generated by high-temperature atomizers that excite multiple elements simultaneously.

Self-absorption occurs when ground-state analyte atoms absorb radiation emitted by excited atoms before detection, decreasing emission intensity. In plasma sources, this effect is minimized due to shorter path length and more uniform temperature distribution compared to flame sources. These characteristics reduce the likelihood of emitted radiation being reabsorbed by ground-state atoms.

Organic solvents enhance spectral line intensities by increasing flame temperature, accelerating feed rate, and producing smaller aerosol droplets. Conversely, salts, acids, and other dissolved species depress emission intensity. Careful sample and standard matching is essential to account for these effects and ensure accurate analyte quantification.

Releasing agents selectively react with interferents to release the analyte from stable compounds formed during flame reactions. Higher temperatures also facilitate dissociation of these stable compounds. These approaches eliminate or moderate chemical interferences, allowing accurate measurement of analyte emission signals.

Inductively coupled plasma atomic emission spectroscopy instrumentation operates at extremely high temperatures that minimize both spectral and chemical interferences. The plasma's abundant electrons offset ionization effects, fewer species remain stable, and the uniform temperature distribution reduces self-absorption, making plasma sources superior to flame sources for interference-prone analyses.