A graphene oxide reinforced polymeric ionic liquids monolith was obtained by copolymerization of graphene oxide doped 1-(3-aminopropyl)-3-(4-vinylbenzyl)imidazolium 4-styrenesulfonate monomer and 1,6-di-(3-vinylimidazolium) hexane bihexafluorophosphate cross-linking agent. Coupled to high-performance liquid chromatography, the monolith was used as a solid-phase microextraction sorbent to analyze several phenolic compounds in aqueous samples. Under the optimized extraction and desorption conditions, linear ranges were 5–400 μg/L for 3-nitrophenol, 2-nitrophenol, and 2,5-dichlorophenol and 2–400 μg/L for 4-chlorophenol, 2-methylphenol, and 2,4,6-trichlorophenol (R2 = 0.9973–0.9988). The limits of detection were 0.5 μg/L for 3-nitrophenol and 2-nitrophenol and 0.2 μg/L for the rest of the analytes. The proposed method was used to determine target analytes in groundwater from an industrial park and river water. None of the analytes was detected. Relative recoveries were in the range of 75.5–113%.
Polyetheretherketone tube is a better substrate for in-tube solid-phase microextraction than fused-silica capillary and metal tube because of its resistance to high pressure and good flexibility. It was modified with a nanostructured silver coating, and characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. It was connected into high-performance liquid chromatography equipment to build the online analysis system by replacing the sample loop of a six-port injection valve. To get the highest extraction capacity, the preparation conditions of the coating was investigated. Important extraction conditions including length of tube, sample volume, and desorption time were optimized using eight polycyclic aromatic hydrocarbons as model analytes. The tube exhibits excellent extraction efficiency toward them, with enrichment factors from 52 to 363. The online analysis method provides good linearity (0.5–100 or 1.0–100 μg/L) and low detection limits (0.15–0.30 μg/L). It has been used to determine polycyclic aromatic hydrocarbons in water samples, with relative recoveries in the range of 92.3–120%. The tube showed highest extraction ability for polycyclic aromatic hydrocarbons, higher extraction ability for hydrophobic phthalates and anilines, and almost no extraction ability for low hydrophobic phenols, due to the possible extraction mechanism including hydrophobic and electron-rich element-metal interactions.
A novel palladium solid-phase microextraction coating was fabricated on a stainless-steel wire by a simple in situ oxidation–reduction process. The palladium coating exhibited a rough microscaled surface and its thickness was about 2 μm. Preparation conditions (reaction time and concentration of palladium chloride and hydrochloric acid) were optimized in detail to achieve sufficient extraction efficiency. Extraction properties of the fiber were investigated by direct immersion solid-phase microextraction of several polycyclic aromatic hydrocarbons and phthalate esters in aqueous samples. The extracted analytes were transferred into a gas chromatography system by thermal desorption. The effect of extraction and desorption conditions on extraction efficiency were investigated. Under the optimum conditions, good linearity was obtained and correlation coefficients between 0.9908 and 0.9990 were obtained. Limits of detection were 0.05–0.10 μg/L for polycyclic aromatic hydrocarbons and 0.3 μg/L for phthalate esters. Their recoveries for real aqueous samples were in the range from 97.1 to 121% and from 89.1 to 108%, respectively. The intra- and interday tests were also investigated with three different addition levels, and satisfactory results were also obtained.
Graphene oxide was bonded onto a silver-coated stainless-steel wire using an ionic liquid as the crosslinking agent by a layer-by-layer strategy. The novel solid-phase microextraction fiber was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy and Raman microscopy. A multilayer graphene oxide layer was closely coated onto the supporting substrate. The thickness of the coating was about 4 μm. Coupled with gas chromatography, the fiber was evaluated using five polycyclic aromatic hydrocarbons (fluorene, anthracene, fluoranthene, 1,2-benzophenanthrene, and benzo(a)pyrene) as model analytes in direct-immersion mode. The main conditions (extraction time, extraction temperature, ionic strength, and desorption time) were optimized by a factor-by-factor optimization. The as-established method exhibited a wide linearity range (0.5–200 μg/L) and low limits of determination (0.05–0.10 μg/L). It was applied to analyze environmental water samples of rain and river water. Three kinds of the model analytes were quantified and the recoveries of samples spiked at 10 μg/L were in the range of 92.3–120 and 93.8–115%, respectively. The obtained results indicated the fiber was efficient for solid-phase microextraction analysis.
The anionic part of ionic liquids can provide additional interactions during chromatographic separations. In this work, the chromatographic separation performance of a silica column functionalized with 1-propyl-3-methylimidazolium chloride ionic liquid was improved by in situ anion-exchange from chloride anions to dodecyl sulfonate anions and dodecylbenzene sulfonate anions. The separation performances of these ionic liquid functionalized phases were investigated and compared with each other using polycyclic aromatic hydrocarbons, phthalates, parabens, and phenols as model compounds. Results indicated that the new columns presented a better chromatographic separation than the original one. This was ascribed retention mechanism from organic anions. The introduction of dodecyl sulfonate anions increased the hydrophobicity of stationary phase. Furthermore, the phenyl groups of dodecylbenzene sulfonate anions could provide an enhanced selectivity to aromatic compounds such as polycyclic aromatic hydrocarbons by π–π interactions. Analysis repeatability of the new columns was satisfactory (RSD of retention time, 0.10–0.40%; RSD of peak area, 0.66–0.84%).
A dicationic imidazolium ionic liquid modified silica stationary phase was prepared and evaluated by reversed-phase/anion-exchange mixed-mode chromatography. Model compounds (polycyclic aromatic hydrocarbons and anilines) were separated well on the column by reversed-phase chromatography; inorganic anions (bromate, bromide, nitrate, iodide, and thiocyanate), and organic anions (p-aminobenzoic acid, p-anilinesulfonic acid, sodium benzoate, pathalic acid, and salicylic acid) were also separated individually by anion-exchange chromatography. Based on the multiple sites of the stationary phase, the column could separate 14 solutes containing the above series of analytes in one run. The dicationic imidazolium ionic liquid modified silica can interact with hydrophobic analytes by the hydrophobic C6 chain; it can enhance selectivity to aromatic compounds by imidazolium groups; and it also provided anion-exchange and electrostatic interactions with ionic solutes. Compared with a monocationic ionic liquid functionalized stationary phase, the new stationary phase represented enhanced selectivity owing to more interaction sites.
