Arsenic sorption and speciation with branch-polyethyleneimine modified carbon nanotubes with detection by atomic fluorescence spectrometry.

Multi-wall carbon nanotubes (MWNTs) are modified with branched cationic polyethyleneimine (BPEI). The MWNTs-BPEI nanocomposites serve as a novel adsorbent and exhibit favorable selectivity toward adsorption of As(V). Appropriate amount of MWNTs-BPEI suspension containing ca. 5 mg of the composites is used to pack a mini-column for on-line solid phase extraction preconcentration of inorganic arsenic in a sequential injection system, following detection by hydride generation atomic fluorescence spectrometry. At pH 5.8, an sorption efficiency of 80% is achieved for As(V) at 10 μg L(-1), resulting in a sorption capacity of 26.18 mg g(-1). Meanwhile, the sorption efficiency for As(III) is <5%. The retained As(V) is readily recovered by 100 μL NH4HCO3 (0.6%, m/v). With a sample volume of 2.0 mL, an enrichment factor of 16.3 for As(V) is obtained along with a detection limit of 14 ng L(-1) within a linear range of 0.05-1.50 μg L(-1). A RSD of 3.6% is derived at 0.5 μg L(-1). Total amount of arsenic is obtained by converting As(III) to As(V) and following the same procedure. The speciation of inorganic arsenic is realized by difference. This procedure is validated by analyzing a certified reference material of human hair (GBW09101), achieving satisfactory agreements between the certified and the obtained values. Speciation of As(V) and As(III) is also performed in snow water and rain water samples.