Multi-walled carbon nanotubes as sorptive material for solventless in-tube microextraction (ITEX2)—a factorial design study

Abstract

Multi-walled carbon nanotubes were evaluated as sorptive packing material for in-tube microextraction (ITEX2) in combination with GC-MS for the analysis of benzene, toluene, ethylbenzene, xylenes, and naphthalene in aqueous samples. For method development, a three-level full factorial design of experiment (DoE) was performed incorporating extraction temperature, number of extraction strokes, and extraction flow. The statistical analysis of method development showed that all considered extraction parameters significantly affected the extraction yield. Furthermore, it was shown that some factors significantly interacted with each other, which indicates the advantage of using DoE for method development. The thereby optimized ITEX2 protocol was validated regarding its linear dynamic range, method detection limit (MDL), and precision. The MDLs of investigated analytes ranged between 2 ng L(-1) for naphthalene and 11 ng L(-1) for p-xylene. The relatively low MDL obtained for naphthalene, despite its comparably low air-water partitioning, can be explained by its strong interaction with carbon nanotubes. All obtained MDLs are at least comparable to previous reports on microextraction techniques, emphasizing both the quality of ITEX2 and the highly promising sorbent characteristics of carbon nanotubes. Furthermore, the method was applied to three real samples, which demonstrated good recoveries of analytes from tap water, a bank filtrate, and an effluent from a wastewater treatment plant.

Investigation of carbon-based nanomaterials as sorbents for headspace in-tube extraction of polycyclic aromatic hydrocarbons

“…An explanation for the higher naphthalene MDL obtained in this work compared to the literature [33] could be the simultaneous extraction of larger molecular size PAHs in this study.…”

“…Extraction yield with CNMs as sorbent Based on previous studies, the extraction temperature, extraction strokes, extraction flow, and desorption temperature were chosen as the most influential parameters for the ITEX extraction procedure [33]. Due to the number of sorbent materials and analytes taken into account, a fast screening approach for method optimization that provides significant data (e.g., BBD) was selected.…”

“…Since all PAHs are present in similar concentrations (Table S4 from the ESM) in the gas phase under equilibrium conditions at the optimal extraction conditions (70°C), the larger PAHs with a stronger sorption to fullerene could have displaced naphthalene and by this caused a higher MDL compared to the reported data [33].…”

“…According to the high F values and low p values in Table 4, the number of strokes and the extraction temperature are the two parameters with the highest influence on the extraction yield [32,33]. In comparison, the extraction flow and desorption temperature are less decisive for the extraction yield.…”

“…After the samples were placed on the TrayCooler, the vials were transported to the SMM, where the samples were heated and stirred at 500 rpm for 15 min [32,33]. For the optimization of the extraction and desorption procedure, four factors (i.e., extraction temperature, extraction strokes, extraction flow, and desorption temperature) at three levels where set Table 1 displays the codification of the factors and levels.…”