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A new method for cadmium determination at ng L−1 levels is described. The method is based on the on-line coupling of a flow preconcentration system using multiwall carbon nanotubes (MWCNT) as sorbent with TS-FF-AAS determination. Cadmium preconcentration was at pH 4.9 onto an MWCNT minicolumn (30 mg) for 2 min at a 5.0 mL min−1 flow rate. The elution step is performed by using 0.5 mol L−1 HNO3 and the cadmium desorbed is directly pumped to a TS-FF-AAS. All experimental parameters that play important roles in system performance were evaluated and optimized by means of fractional factorial designs and response surface methodology. The excellent characteristics of MWCNT as sorbent, mainly owing to its high surface area, make it possible to obtain a preconcentration factor of 51-fold, thus improving the detection and quantification limits in TS-FF-AAS, 11.4 and 38.1 ng L−1, respectively …