Flame atomic absorption spectrometric determination of lead and cadmium after solid phase extraction using magnetic multi-walled carbon nanotubes modified with polythiophene

Heavy metals such as lead and cadmium have serious toxic effects on living organisms due to their cumulative nature [1]. Lead and cadmium are known as the carcinogenic agents with irreversible effects on human’s body which causes a variety of diseases and undesired health consequences [2]. The main sources of these metal ions for humans and animals are food, water, and atmosphere. Sensitive and reliable analytical techniques have an important role to evaluate the impacts of metal pollutants. However, due to the existence of lead and cadmium at very low levels in environmental and biological samples, a separation/preconcentration process is usually required prior to their determinations by instrumental analytical techniques [3].In the present study, polythiophene (PT) coated magetic multi-walled carbon nanotubes (MMWCNT) as the magnetic solid phase extraction (M-SPE) sorbent was synthesized and characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and scanning electron microscopy (SEM). The sorbent was applied for the separation and preconcentration of trace amounts of lead and cadmium ions from aqueous solutions before their determinations by flame atomic absorption spectrometry. The main factors affecting the extraction of lead and cadmium such as pH, type and concentration of eluent, the amount of sorbent, ionic strength and the sample volume were investigated and optimized. Under the optimized conditions, the detection limits of lead and cadmium were found to be 0.54 and 0.03 µg L-1, respectively. The enhancement factors of 198 and 196 were obtained for lead and cadmium, respectively. The relative standard deviations (n = 6) at 50.0 µg L-1 of lead and 5.0 µg L-1 of cadmium were 1.5% and 2.1%, respectively. The method was successfully applied to the determination of lead and cadmium in water, hair, nail, black tea and rice samples. The validity of the method was examined through the recovery experiments and independent analysis by electrothermal atomic absorption spectrometry.