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 o f the most frequently used modifiers for lead determination in water s amples by ETAAS, These modifiers include NH4H2PO4, Pd, Pd-Mg, Pd-NH4H2 PO4, Mg-NH4H2PO4, Ni-NH4H2PO4 and Ni-Sr-NH4H2PO4. The comparison of an alytical characteristics is based mainly on the common requirements fo r the direct analysis of water samples, which include maximum allowabl e pyrolysis temperature, tolerable interference, characteristic mass ( sensitivity) and sample recovery, Overall, Ni-Sr-NH4H2PO4 performs bet ter than the others in all aspects cited above, Pd-based modifiers beh ave very similarly except that the sensitivity using Pd-NH4H2PO4 is sl ightly lower, The use of Ni-Sr-NH4PO4 raises the maximum tolerable pyr olysis temperature to 1300 degrees C, which is significantly higher th an that of the other modifiers, Similarly, the permissible amounts of chloride and sulfate interference are higher with the Ni-Sr-NH4H2PO4 m odifier, The characteristic masses (m(o)) for the modifiers NH4H2PO4, Pd, Pd-Mg, Pd-NH4H2PO4, Mg-NH4H2PO4, Ni-NH4H2PO4 and Ni-Sr-NH4H2PO4 ar e 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 contra st, the lead recoveries with other modifiers are 53-90%.