Investigation of chemical modifiers for the determination of lead in fertilizers and limestone using graphite furnace atomic absorption spectrometry with Zeeman-effect background correction and slurry sampling

In this work, chemical modifiers in solution (Pd/Mg, NH4H2PO4 and NH4NO3/Pd) were compared with permanent modifiers (Ir and Ru) for the determination of lead in fertilizer and limestone samples using slurry sampling and graphite furnace atomic absorption spectrometry with Zeeman-effect background correction. The analytical line at 283.3 nm was used due to some spectral interference observed at 217.0 nm. The NH4H2PO4 was abandoned due to severe spectral interference even at the 2833-nm line. For Pd/Mg and NH4NO3/Pd the optimum pyrolysis and atomization temperatures were 900 degrees C and 1900 degrees C, respectively. For Ru and Ir, the integrated absorbance signal was stable up to pyrolysis temperatures of 700 degrees C and 900 degrees C, respectively, and up to atomization temperature of 1700 degrees C. The limit of detection (LOD) was 17 ng g(-1) using Pd/Mg and 29 ng g(-1) using NH4NO3/Pd. Among the permanent modifiers investigated, the LOD was 22 ng g(-1) Pb for Ir and 10 ng g(-1) Pb for Ru. The accuracy of the method was evaluated using the certified reference material NIST SRM 695. Although Ru provided lower LOD, which can be attributed to a lower blank signal, only the modifiers in solution showed concordant values of Pb concentration for the NIST SRM 695 and the most of analyzed samples. Moreover, the Pd/Mg modifier provided the highest sensitivity and for this reason it is more suitable for the determination of Pb in fertilizers samples in slurry; besides this it presented a better signal-to-noise ratio than NH4NO3/Pd. (C) 2013 Elsevier B.V. All rights reserved.