Minimizing matrix effects and spectral interferences produced by Fe absorption lines in the determination of cadmium by electrothermal atomic absorption spectrometry: Application to the fractionation of cadmium in moderated contaminated soils

Solutions, including the extracting solutions used in the sequential procedure recommended by the Standard, Measurements and Testing Program, with different cadmium and iron concentrations were prepared and analyzed using combined electrothermal atomic absorption spectrometry (ETAAS) and two background compensation techniques. The first was based on the deuterium background correction method in which a deuterium lamp was used in combination with a conventional Cd hollow-cathode lamp. For the second, a high-intensity boosted discharge hollow-cathode lamp (BDHCL) was used as in the Smith-Hieftje (S-H) background correction method, but this lamp was modulated with a low and a high current mode at a modulation frequency of 100 Hz. In the present study, the modulation cycle was 10 times higher than in the S-H system. Therefore, the background correction method was called high-speed self-reversal method. Pseudo-total Cd concentrations were determined using ETAAS in five reference materials and fractionation was made in two reference soils. With regard to the results, the high-speed self-reversal background correction method provided a method of choice to eliminate or decrease the spectral interference due to the close positioning of the analytical lines of Cd and Fe in solutions containing high iron concentrations during the Cd determination by electrothermal atomic absorption spectrometry. It is worth noting that using the HSSR-method, the sensitivity losses were from 32% to 39% compared to the continuum source background corrector equipped with a deuterium lamp. The HSSR-method was successfully applied to the determination of Cd in contaminated samples. The results showed that interferences caused by absorption line overlapping of Cd and Fe could be compensated accurately for Fe/Cd = 100,000 in 0.11 M acetic acid and Fe/Cd < 10,000 in 0.5 M hydroxylamine hydrochloride.