A novel strategy to increase performance of solid‐phase microextraction fibers: Electrodeposition of sol‐gel films on highly porous substrate

In the present work, the effect of substrate porosity for preparation of solid‐phase microextraction (SPME) fibers was investigated. The fibers were prepared by electrodeposition of sol‐gel coatings using negative potentials on porous Cu wire and compared with previous reported technique for preparation of SPME fibers using positive potentials on smooth gold wire. Porous substrate was prepared by electrodeposition of a thin layer of Cu on a Cu wire. The extraction capability of prepared fibers was evaluated through extraction of some aromatic hydrocarbons from the headspace of aqueous samples. The effect of substrate porosity and some operating parameters on extraction efficiency was optimized. The results showed that extraction efficiency of SPME fibers highly depends on porosity of the substrate. The LOD ranged from 0.005 to 0.010 ng/mL and repeatability at the 1 ng/mL was below 12%. Electrodeposited films were characterized for their surface morphology and thermal stability using SEM and thermogravimetric analysis, respectively. SEM analysis revealed formation of porous substrate and subsequently porous coating on the wire surface and thermogravimetric analysis showed high thermal stability of the prepared fiber.     

A Modified Nanoporous Silica Aerogel as a New Sorbent for Needle Trap Extraction of Chlorobenzenes from Water Samples

In this work, a modified nanoporous silica aerogel was used as a new sorbent for headspace needle trap extraction of chlorobenzenes from aqueous samples. The needle trap extraction is derived from solid-phase microextraction and the sorbent is inside the needle. The thermal stability and functional groups of the sorbent were studied by TG/DTA and FT-IR, respectively. The modified silica aerogels, characterized by field emission scanning electron microscopy, showed a three-dimensional network containing a homogeneous pore structure with pore sizes of a few tens of nm and a sponge-like microstructure. The developed method was applied to the trace level extraction of some chlorobenzene compounds from aqueous samples. The influential parameters on the extraction efficiency, including the extraction temperature, ionic strength and extraction time were investigated and optimized. Under optimized conditions, the detection and quantification limits were in the range of 0.4–0.8 and 1–3 ng L^?1, respectively. The relative standard deviation values for water spiked with chlorobenzenes at 100 ng L^?1 under optimum conditions were 3–7%. The dynamic linear range of the method in the range of 3–3000 ng L^?1 was investigated. Finally, the current method for the analysis of real water samples containing spiked chlorobenzenes was applied and the relative recovery values were found to be in the range of 96–101%.     

Chemically Deposited Sol–Gel Film on Porous TiO<Subscript>2</Subscript> Nanotube Arrays as an Efficient and Unbreakable Solid-Phase Microextraction Fiber

In the present study, a novel technique was proposed to improve the performance of solid-phase microextraction fibers through the chemical deposition of polydimethylsiloxane/divinylbenzene film on modified TiO₂ nanotube arrays substrate. Two different techniques, including the self-assembled monolayer of 3-mercaptopropyl trimethoxysilane and NaOH treatment, were examined to modify the surface of TiO₂ nanotube arrays. The morphology of the prepared fibers was studied by scanning electron microscopy. The applicability of the novel fiber was evaluated through the headspace solid-phase microextraction of some polycyclic aromatic hydrocarbons as the model compounds followed by GC–MS determination. Influencing parameters on the extraction efficiency such as extraction time, temperature and salt content were studied and optimized. The thermal stability experiments demonstrated that the novel fiber was stable at 280 °C and reusable for more than 80 times without an obvious decrease in the extraction performance. The proposed method was successfully applied to the determination of PAHs in river water samples with good relative recoveries from 75.8 to 104.5% and the relative standard deviation values for all analytes were below 12%. Finally, the extraction performance of the prepared fiber was compared with those of commercially available fibers and similar previously reported fibers.     

Distinguishing sources of N2O in European grasslands by stable isotope analysis

Nitrifiers and denitrifiers are the main producers of the greenhouse gas nitrous oxide (N(2)O). Knowledge of the respective contributions of each of these microbial groups to N(2)O production is a prerequisite for the development of effective mitigation strategies for N(2)O. Often, the differentiation is made by the use of inhibitors. Measurements of the natural abundance of the stable isotopes of N and O in N(2)O have been suggested as an alternative for the often unreliable inhibition studies. Here, we tested the natural abundance incubation method developed by Tilsner et al.1 with soils from four European grasslands differing in long-term management practices. Emission rates of N(2)O and stable isotope natural abundance of N(2)O and mineral N were measured in four different soil incubations: a control with 60% water-filled pore space (WFPS), a treatment with 60% WFPS and added ammonium (NH(4) (+)) to support nitrifiers, a control with 80% WFPS and a treatment with 80% WFPS and added nitrate (NO(3) (-)) to support denitrifiers. Decreases in NH(4) (+) concentrations, linked with relative (15)N-enrichment of residual NH(4) (+) and production of (15)N-depleted NO(3) (-), showed that nitrification was the main process for mineral N conversions. The N(2)O production, however, was generally dominated by reduction processes, as indicated by the up to 20 times larger N(2)O production under conditions favouring denitrification than under conditions favouring nitrification. Interestingly, the N(2)O concentration in the incubation atmospheres often levelled off or even decreased, accompanied by increases in delta(15)N and delta(18)O values of N(2)O. This points to uptake and further reduction of N(2)O to N(2), even under conditions with small concentrations of N(2)O in the atmosphere. The measurements of the natural abundances of (15)N and (18)O proved to be a valuable integral part of the natural abundance incubation method. Without these measurements, nitrification would not have been identified as essential for mineral N conversions and N(2)O consumption could not have been detected.     

Pharmacokinetic study and the extraction efficiency of bulk and precipitated ibuprofen-imprinted polymer sorbents for gas chromatography and gas chromatography-mass spectrometry ibuprofen bio-analysis

Bulk and precipitation polymerization methods were used to prepare ibuprofen-molecularly imprinted polymers. Molecularly imprinted polymer-bulk and -precipitation were synthesized in acetonitrile, likewise molecularly imprinted polymer-bulk (mixture) and molecularly imprinted polymer-precipitation (mixture) in a mixture of acetonitrile/toluene (75:25 v/v). N₂ adsorption-desorption analysis data revealed that molecularly imprinted polymer-precipitation (mixture) has the highest specific surface area (200.74 m²/g). The surface chemistry and morphology of the synthesized sorbents were investigated by Fourier-transform infrared analysis and scanning electron microscope micrographs respectively. The prepared sorbents in the mixture of solvents were used in a dispersive solid-phase extraction process for selective extraction and pre-concentration of ibuprofen from urine and human plasma samples. The detection limits were 62.91 and 7.89 ng/ml using molecularly imprinted polymer-bulk (mixture) and molecularly imprinted polymer-precipitation (mixture), respectively. Also, the sorbents showed selective behavior to extract ibuprofen in the presence of naproxen, fenoprofen, and ketoprofen. Overall, the results showed that the precipitation method in the mixture of acetonitrile/toluene resulted in the preparation of a sorbent with the highest extraction efficiency. Furthermore, a pharmacokinetic study was done. The maximum plasma concentration, the time required for maximum plasma concentration, and plasma half-life were 28.95 μg/ml, 2, and 2.39 h, respectively.     

Electroless deposition of silver nanofractals on copper wire by galvanic displacement as a simple technique for preparation of porous solid‐phase microextraction fibers

A novel and porous solid‐phase microextraction fiber was prepared by quick and simple galvanic displacement reaction and applied to the determination of some polycyclic aromatic hydrocarbons in sunflower oil. The parameters affecting the porosity and thickness of the fiber, and parameters affecting the extraction efficiency, including the extraction time, temperature, and ionic strength, were investigated and optimized. The morphology of prepared fiber was characterized by optical and scanning electron microscopy and thermal and chemical stabilities of the fiber were studied. Under the optimum conditions, the limits of detection ranged between 0.1 ng/mL for pyrene to 1.2 ng/mL for anthracene, and LOQ ranged between 0.3 ng/mL for pyrene to 3.6 ng/mL for anthracene. The relative standard deviations, including repeatability (within fibers) and reproducibility (between fibers), varied between 3.2–8.9 and 5.6–9.8%, respectively.