Calcium alginate caged multiwalled carbon nanotubes for the pre-concentration of polycyclic aromatic hydrocarbons from environmental water samples

Abstract

Monitoring of polycyclic aromatic hydrocarbons (PAHs) in water samples is important for human protection due to the carcinogenicity and mutagenicity of these compounds. A new technique termed dispersive micro solid phase extraction (D-µ-SPE) based on multiwalled carbon nanotubes (MWCNTs) caged in calcium alginate (Ca+2-Alg) was developed and applied for efficient extraction of PAHs from environmental water samples. The prepared adsorbent (Ca-Alg-MWCNTs) was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and thermal gravimetry analysis. The hydrophilicity of the Ca+2-Alg cage enhances the dispersibility of the adsorbent in water samples and the MWCNTs core facilitates separation of PAHs. The composite beads not only make full use of the good PAHs adsorption properties of alginate and MWCNTs, but also prevent MWCNTs from breaking off from the composites to cause secondary micro-pollution to water. The proposed D-µ-SPE method was applied successfully for the extraction of selected PAHs from environmental water samples. The D-µ-SPE technique provides reasonable extraction time (30 min) to extract trace levels of PAHs from 100 mL of water samples with 100 mg of adsorbent. The extracted PAHs were desorbed by 0.1 mL of ethyl acetate to give enrichment factor of 1000. Under the optimized conditions, the detection limits for fluorene, phenanthrene and fluoranthrene were 0.42 ng mL-1, 0.3 ng mL-1 and 0.22 ng mL-1, respectively. The recoveries of several spiked real water samples for PAHs were in the range of 71.2-104.2% with good relative standard deviations (1.2% - 7.2%), showing good reproducibility of the method. The potential benefits of the D-µ-SPE using Ca-Alg-MWCNTs include high extraction efficiency, short analysis time and convenient extraction procedure. Thus D-µ-SPE method based on Ca-Alg-MWCNTs is a suitable candidate for use as an alternative adsorbent in the simultaneous pre-concentration of PAHs from environmental water samples.