Semi-online preconcentration of Cd, Mn and Pb on activated carbon for GFASS

This paper presents a method whereby trace elements in NH4Cl–NH3 medium are adsorbed on activated carbon in a micro-flow-injection (FI) semi-online sorbent extraction preconcentration system and then determined by graphite furnace atomic absorption spectrometry (GFAAS). The analytical performance of the proposed method for determining Cd, Mn and Pb was studied. A microcolumn packed with activated carbon was used as a preconcentration column (PCC). The metals to be determined were preconcentrated onto the column for 60 s and then rinsed with 0.02% (v/v) HNO3 and eluted with 30 μl of 2 mol l−1 HNO3. Compared with the direct injection of 30 μl of aqueous sample solution, enrichment factor of 32, 26, and 21 and detection limits (3σ) of 0.4, 4.7, and 7.5 ng l−1 for Cd, Mn and Pb, respectively, were obtained with 60 s sample loading at 3.0 ml min−1 for sorbent extraction, 30 μl of eluate injection, and peak area measurement. The precisions (RSD, n=6) were 2.8% at the 0.05 μg l−1 level for Cd, 3.0% at the 0.3 μg l−1 level for Mn, and 3.1% at the 0.5 μg l−1 level for Pb. The experimental results indicate that the procedure can eliminate the fundamental interferences caused by alkali and alkaline earth metals and the application of it to the determination of Cd, Mn and Pb in some water samples is successful.