Combined Nickel and Phosphate Modifier for Lead Determination in Water by Electrothermal Atomic Absorption Spectrometry

Abstract

The effectiveness of nickel nitrate plus ammonium dihydrogenphosphate as a combined modifier for the determination of lead in a variety of water samples by ETAAS was evaluated. Optimization of the temperature program, modifier mass and pyrolysis hold time for the determination of lead was carried out. The results indicate that the combined modifier allows the quantitative stabilization of Pb in water samples up to 1200 °C during the pyrolysis step. In comparison, the maximum pyrolysis temperature without the modifier is 900 °C or lower. The modifier further reduces the background absorbance caused by sample matrices and significantly enhances the sensitivity of Pb determination. The observed detection limit is 0.14 µg l ^-1 with a sample volume of 10 µl. The characteristic mass or sensitivity of the proposed method is 7 pg. The tolerable amounts of various interferents such as chloride, sulfate and carbonate in the presence of the modifier are high enough for the determination of lead in a variety of waters. The recoveries of spiked Pb in tap water and waters from variably contaminated waters from a ditch, a lake and a river in the Chicago area were 89–101%. The proposed method has several advantages over commonly used methods with H ₃ PO ₄ or Mg(NO ₃ ) ₂ +NH ₄ H ₂ PO ₄ as modifiers.