MAINTENANCE OF THE SLOPE OF LINEARIZED CALIBRATION CURVES IN ZEEMAN GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY

L'vov and co-workers developed a theoretical model and computational p rocedure (B.V. L'vov, L.K. Polzik and N.V. Kocharova, Spectrochim. Act a Part B, 47 (1992) 889 and B.V. L'vov, L.K. Polzik, N.V. Kocharova, Y u.A. Nemets and A.V. Novichikhin, Spectrochim. Acta Part B, 47 (1992) 1187) that linearized calibration curves in Zeeman graphite furnace at omic absorption spectrometry by taking into account the presence of st ray light. The calculations of L'vov and co-workers were based on thre e parameters: the rollover absorbance A(r), Zeeman sensitivity ratio R , and the original background corrected peak absorbance values A(z). I n order to simplify the calculations, R was assumed to be unity. In th e studies reported here, this simplification is shown to be unsatisfac tory because the slope obtained in the upper portion of the calibratio n curve, after linearization, is found to be different from the slope obtained in the normal linear region. Deviations between these slopes were found to be as high as 30%. The present work also shows that the theoretical model of L'vov and co-workers does not have a mathematical solution at high values of A(z). This failure of the model prevents i ts use at high A(z) values. The physical nature of this failure is sti ll unclear, which points to the necessity for further work to understa nd the inadequacies of the present theory, In the present studies, cal culations based on the Newton method of successive approximations (A.I . Yuzefovsky, E.G. Su, R.G. Michel, W. Slavin and J.T. McCaffrey, Spec trochim. Acta Part B, 49 (1994) 1643), allow incorporation of the expe rimental value of R at the rollover point R', which better linearizes the calibration curves. By use of this approach, a satisfactory result is obtained for lead (R' = 0.67) up to the point of failure of the mo del at high values of A(z).