The system was then switched, after 4.5 min, and the Pb2þ was eluted from the RACNTs' column, and analyzed in the TS-FF-AAS. The absence of proteins in the system during the TS-FF-AAS analyses can be shown by the very low background, as well as by the same behavior of the thermo spray in the extraction and elution steps (Fig. 1a and b). It is important to emphasize that the thermospray stops when a serum sample is injected directly in the system without the RACNTs' column. This fact is a consequence of the high level of proteins in the sample as well as its high viscosity