Determination of Heavy Metals at Sub-ppb Levels in Water by Graphite Furnace Atomic Absorption Spectrometry Using a Direct Introduction Technique after Preconcentration with an Iminodiacetate Extraction Disk

Abstract

A direct analysis method combining an iminodiacetate extraction disk (IED) with graphite furnace atomic absorption spectrometry was developed for the determination of Co, Ni, Cu, Cd, Sn, Pb, and Bi at sub-ppb levels in water. A 100 mL water sample was adjusted to pH 5.6 with nitric acid and a 1 mol?L –1 ammonium acetate solution, and then passed through an IED (diameter, 47 mm; effective filtering diameter, 35 mm) at a flow rate of 80 - 100 mL?min –1 to preconcentrate seven analytes. The IED was dried at 100?C for 20 min in an electric oven, and 110 - 145 small disks, each 2 mm in diameter, were punched out from the IED. A small disk was introduced into the graphite furnace and atomized according to a heating program. For Cd, Sn, Pb, and Bi measurements, Pd was used as a chemical modifier to enhance the absorbances. Calibration was performed using aqueous standard solutions. The detection limits, corresponding to three times the standard deviation ( n = 5) of the blank values, were 0.092 μg·L –1 for Co, 0.12 μg·L –1 for Ni, 0.40 μg·L –1 for Cu, 0.077 μg·L –1 for Cd, 0.92 μg·L –1 for Sn, 0.61 μg·L –1 for Pb, and 0.80 μg·L –1 for Bi with an enrichment factor of 140 using a 100-mL water sample. A spike test for the seven analytes in tap water, rainwater, river water, and mineral drinking water showed quantitative recoveries (93% - 108%).