Problems involved in the calculation of theoretical sensitivities of flame atomic absorption measurements

Abstract

Theoretical sensitivities cannot replace calibration. Nevertheless, they are important for standardless atomic absorption determinations, and especially, for optimization of experimental conditions. Starting with fundamental processes involved in the interaction of electromagnetic radiation with the matter, a simple sensitivity formula was derived.

$$S_A = [dA(\lambda _0 )/dc_A ]_0 = K_n (b/D)(\rho /M_A )\lambda _0 G$$

The sensitivityS _A is the initial slope of the calibration curve absorbanceA(λ₀) measured at the centre λ₀ of the resonance line vs. concentrationc _A of the element to be determined (analyteA). The relative atomic massM _A of the analyte and the density ϱ of the solutions need no further discussion here. The ratio (b/D) of the absorption path length b to the dilution factor determines the sensitivity of determinations by AAS to a high degree and. will be discussed in detail. The numerical factorK _n depends on the concentration unit and the system of units (CGS or SI) used for the physical constant involved. The former were always used in earlier works in the field of atomic spectroscopy. In order to make a connection more easily between classic (CGS) and modern (SI) formulations, the most important equations are given in both systems of units. The other important factors are combined in the group G-factors of dimension one. The comparison of the theoretical and experimental sensitivities may be transformed to the comparison of theoretical and experimental G-values. Whereas the comparison of sensitivities is always limited to an experimental set-up, the comparison ofG-values is released from this “ballast” and therefore will be preferred here. It is proposed that experimentalG-values are computed from experimental sensitivities and used for compilations in the future, because they are more precise and accurate than their cofactors.