Background Correction Methods in Atomic Absorption Spectroscopy

Abstract

AbstractAtomic absorption spectroscopy (AAS) is based on the absorption of element‐specific primary source radiation by analyte atoms. If part of the radiation isabsorbed by molecules or lost due to scattering, a higher gross absorbance is measured. The difference between the net absorption of the analyte atoms and the measured gross absorbance is called background absorbance. Background absorption and scattering effects have much more serious effects on the results produced in electrothermal atomization atomic absorption spectroscopy (ETAAS) than flame atomic absorption spectroscopy (FAAS).The amount of incident light deflected or absorbed by nonatomic species must be measured to obtain the correct, net absorbance of the analyte atoms only. Perfect background correction can be obtained only when the background absorbance measurement corresponds exactly in space, time and wavelength with the atomic absorbance measurement. Since exact coincidence of all three parameters is obviously impossible, it is customary to give priority to the equality in space and to make the difference in time and/or wavelength as small as possible. Although molecular absorption and radiation scattering are both broad‐band phenomena, there is no spectral range where constant background attenuation can be guaranteed.In all background correction systems two measurements are made. The total or gross absorbance is measured at the wavelength of the resonance line emitted by the hollow cathode lamp (HCL). The background attenuation is then subtracted from the measured analyte absorbance to obtain the analyte absorbance. There are several ways in which the nonatomic absorption at the resonance wavelength can be estimated, including two‐line background correction, continuum‐source or deuterium lamp background correction, Zeeman background correction, pulsed lamp or Smith–Hieftje background correction and wavelength‐modulation correction methods. The principle of each method, the instrumentation and applications are discussed. Continuum‐source background correction is widely used in FAAS and ETAAS, whereas Zeeman background correction and pulsed lamp background correction are often preferred in ETAAS.