Simulation of a continuum-source atomic absorption spectrometer

Abstract

Continuum source atomic absorption spectrometry becomes a method for simultaneous multi-element analysis leading to a renewed interest in this method. The linear range of the calibration curve and the detection limits of continuum source atomic absorption spectrometers depend on the parameters of the instrumental function of the spectral instrument and the absorption line, the intensity of the radiation source, the level of radiation scattered in the instrument, and other factors. Calculating these dependences was the aim of this work. A theoretical model of the process of the absorption signal formation was constructed, and a computer program for its simulation was developed. Adequacy of the simulation was verified by comparing the absorption signals and calibration curves with the experimental ones obtained on a Grand-AAS spectrometer for several elements: Cd 228.8022 nm, Be 234.8610 nm, Mn 279.4817 nm, and Pb 283.3053 nm, as well as for the Ag 338.289 nm line recorded by two polychromators with different spectral resolution and scattered radiation levels. The relative deviation of the measured analytical signal from the simulated one did not exceed 15% in the concentration range of five orders of magnitude. The simulation results showed that nonlinearity of the calibration curve was primarily determined by the ratio of the width of the instrumental function (resolution) of the spectral instrument to the absorption line. The contribution of scattering in the spectrometer to the nonlinearity was secondary. The influence of the aperture characteristics of the photodetector arrays on the analytical signal was not significant. It was shown that decreasing resolution of the spectral instrument resulted in expanding the linear part of the calibration graphs from above to the level determined by scattering in the spectrometer. The detection limits limiting the graphs from below decrease with decreasing resolution until it approaches twice the width of the element's absorption line. After that, they start to increase.