The possibility to use multi-walled carbon nanotubes as a sorbent for dispersive solid phase extraction of selected pharmaceuticals and their metabolites: Effect of extraction condition

This article presents a dispersive solid phase extraction (dSPE) method combined with liquid chromatography-chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) for the simultaneous isolation and quantification of eight pharmaceuticals and their selected metabolites (metronidazole, sulfamethoxazole, N-acetylsulfamethoxazole, diclofenac, 4-hydroxydiclofenac, 5-hydroxydiclofenac, naproxen and 6-O-desmethylnaproxen) in environmental water samples. Interestingly, in the developed method, multi-walled carbon nanotubes (MWCNTs) were used as a sorbent due to their extraordinary sorption capacity. Key parameters that influence the efficiency of the analytical extraction procedure, such as the type and amount of sorbent, the pH of the sample solution and the composition and volume of the elution solvent have been determined. Significant differences in sorption affinity were observed depending on the pH of the sample. To explain these differences, a computational study was carried out to examine the effect of environmental conditions (different pH levels) on the geometry of the structures sulfamethoxazole, N-acetylsulfamethoxazole, diclofenac (described by the variety of structural properties). It is worth noting that only 4 mg of CNTs (with outer diameter < 8 nm) allowed to achieve 100% sorption for all target analytes. The analytes were eluted with 10 mL of a mixture of ACN:CH3COOH (3:7, v/v). Under the optimal conditions, detection limits and linearity were achieved in the range of 0.01-0.08 mu g L-1 and 0.02-2.5 mu g L-1, respectively. The application potential of the developed methodology for the effective extraction of eight pharmaceuticals from surface and waste water samples was assessed by determining the matrix effects. The developed extraction technique can be considered as a green, mainly due to very low consumption of organic solvent and solid sorbent, fast and low-labor procedure, and the possibility of reuse of the sorbent.