Determination of ultra-trace amounts of cadmium by ET-AAS after column preconcentration with a new sorbent of modified MWCNTs.

The present research reports on the application of modified multiwalled carbon nanotubes as a new, easily prepared, and stable solid sorbent for the column preconcentration of ultra-trace amounts of cadmium in aqueous solution. Multiwalled carbon nanotubes were oxidized with concentrated HNO3 and modified with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol and then were used as a solid phase for the column preconcentration of Cd(II). Elution was carried out with 0.5 mol L(-1) HNO3. The amount of eluted Cd(II) was measured using electrothermal atomic absorption spectrometry. Various parameters such as pH, sample and eluent flow rate, eluent concentration, breakthrough volume, and interference of a great number of anions and cations on the retention of analyte on sorbent were studied. Under the optimized conditions, the calibration graph was linear in the range of 0.67 ng L(-1) to 5.0 μg L(-1) and the detection limit (3Sb, n = 7) was 0.14 ng L(-1) in initial solution. A preconcentration factor of 300 and relative standard deviations of ± 3.6 % for seven successive determinations of 3 ng of Cd(II) were achieved. The column preconcentration was successfully applied to the analysis of river water, waste water, and Persian Gulf water sample.