Comparison of chemical modifiers for the determination of lead in water samples with electrothermal atomic absorption spectrometry

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-NH4PO4 raises the maximum tolerable pyrolysis temperature to 1300 degrees 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%.