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 NH ₄ H ₂ PO ₄ , Pd, Pd–Mg, Pd–NH ₄ H ₂ PO ₄ , Mg–NH ₄ H ₂ PO ₄ , Ni–NH ₄ H ₂ PO ₄ and Ni–Sr–NH ₄ H ₂ PO ₄ . 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–NH ₄ H ₂ PO ₄ performs better than the others in all aspects cited above. Pd-based modifiers behave very similarly except that the sensitivity using Pd–NH ₄ H ₂ PO ₄ is slightly lower. The use of Ni–Sr–NH ₄ H ₂ PO ₄ 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–NH ₄ H ₂ PO ₄ modifier. The characteristic masses ( m _o ) for the modifiers NH ₄ H ₂ PO ₄ , Pd, Pd–Mg, Pd–NH ₄ H ₂ PO ₄ , Mg–NH ₄ H ₂ PO ₄ , Ni–NH ₄ H ₂ PO ₄ and Ni–Sr–NH ₄ H ₂ PO ₄ 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–NH ₄ H ₂ PO ₄ modifier. By contrast, the lead recoveries with other modifiers are 53–90%.