Multiwalled carbon nanotubes as solid sorbent in dispersive micro solid-phase extraction for the sequential determination of cadmium and lead in water samples

Abstract

The combination of dispersive micro solid-phase extraction (DMSPE) with high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GFAAS) was developed for the sequential determination of cadmium and lead in water samples. During the preconcentration step the multiwalled carbon nanotubes (MWCNTs) were used as solid sorbent. MWCNTs were dispersed in water samples containing trace elements to be determined. The samples were mixed for 5min. After the sorption, the aqueous samples were separated by centrifugation. Then, the metal loaded MWCNTs were suspended using a small volume of deionized water and introduced to the atomizer. The experimental parameters including the pH of sample solution, amount of MWCNTs, sample volume and extraction time, as well as main parameters of HR-CS GFAAS were investigated. The concentration limits of detection were 0.001 and 0.03μgL−1 for Cd and Pb, respectively. The preconcentration factors achieved for Cd and Pb were 30 and 15, respectively. The relative standard deviations (RSDs) were 3% and 4% for Cd and Pb, respectively. The accuracy of this method was validated by analyses of NIST SRM 1643e (Trace Elements in Water) and ERM-CA011b (Hard Drinking Water). The measured element contents in these reference materials were in satisfactory agreement with the certified values according to the t-test for a 95% confidence level. The proposed method has been successfully applied for the determination of cadmium and lead in four different water samples (seawater, lake water, mine water and tap water).