CONCENTRATION CURVES IN ATOMIC-ABSORPTION SPECTROMETRY

A detailed analysis of the correlation between the number of absorbing atoms, N, and the absorbance, A, produced by them, i.e. A = f(N), is given. This analysis is valid for any optical thickness of the absorbing layer and accounts for Doppler broadening and pressure broadening of the emission and absorption lines, hyperfine structure and collisional shift as well as spatial temperature distribution and analyte distribution non-uniformities of the absorbing layer. It is shown that all the spectral features lead to curvature and a decreasing of the slope of the initial portion of the concentration curves. However, these effects are considerable only for analysis lines that consist of widely spaced hyperfine components, High stability of the concentration curves to variations of parameters defining the profile of the analysis line is shown. Parameters of the concentration curves, sensitivity, characteristic concentrations, curvature coefficient, and linearity range are introduced and calculated. Spatial non-uniformities of the absorbing layer affect the concentration curves much more strongly than the above spectral features of the analysis line. It is shown that the spatial non-uniformities act in two different ways: longitudinal temperature and concentration gradients result in a decrease in the slope of the concentration curves while cross-sectional non-uniformities lead to curvature of the concentration curves. It is suggested that the lateral non-homogeneity of the analyte distribution is a main cause of the curvature of analytical working curves in GFAAS.