Comparison of Chemical Modifiers for the Determination of Lead in Water Samples With Electrothermal Atomic Absorption Spectrometry

Abstract

A comprehensive comparison is made of the analytical characteristics of the most frequently used modifiers for lead determination in water samples by ETAAS. These modifiers include NH₄H₂PO₄, Pd, Pd–Mg, Pd–NH₄H₂PO₄, Mg–NH₄H₂PO₄, Ni–NH₄H₂PO₄ and Ni–Sr–NH₄H₂PO₄. The comparison of analytical characteristics is based mainly on the common requirements for the direct analysis of water samples, which include maximum allowable pyrolysis temperature, tolerable interference, characteristic mass (sensitivity) and sample recovery. Overall, Ni–Sr–NH₄H₂PO₄ performs better than the others in all aspects cited above. Pd-based modifiers behave very similarly except that the sensitivity using Pd–NH₄H₂PO₄ is slightly lower. The use of Ni–Sr–NH₄H₂PO₄ raises the maximum tolerable pyrolysis temperature to 1300 °C, which is significantly higher than that of the other modifiers. Similarly, the permissible amounts of chloride and sulfate interference are higher with the Ni–Sr–NH₄H₂PO₄ modifier. The characteristic masses (m_o) for the modifiers NH₄H₂PO₄, Pd, Pd–Mg, Pd–NH₄H₂PO₄, Mg–NH₄H₂PO₄, Ni–NH₄H₂PO₄ and Ni–Sr–NH₄H₂PO₄ are 6.1, 8.8, 7.9, 11.6, 10.5, 7.0 and 4.5 pg, respectively, whereas m_o is 12.1 without modifiers. The lead recoveries in samples of natural and tap waters are 72–94% with the Ni–Sr–NH₄H₂PO₄ modifier. By contrast, the lead recoveries with other modifiers are 53–90%.

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