Carboxylated Multiwalled Carbon Nanotubes as Dispersive Solid-Phase Extraction Sorbent to Determine Eighteen Polychlorinated Biphenyls in Vegetable Samples by Gas Chromatography-Mass Spectrometry

Figure 3

Photography of cleanup efficiency using different d-SPE absorbents: (a), without cleanup; (b), MWCNTs-COOH; (c), C18; (d), PSA; (e), GCB.