Low-density magnetofluid dispersive liquid–liquid microextraction for the fast determination of organochlorine pesticides in water samples by GC-ECD

A new micro-extraction technique named low-density magnetofluid dispersive liquid–liquid microextraction (LMF-DMMLE) has been developed, which permits a wider range of solvents and can be combined with various detection methods. Comparing with the existing low density solvents micro-extraction methods, no special devices and complicated operations were required during the whole extraction process. Dispersion of the low-density magnetofluid into the aqueous sample is achieved by using vortex mixing, so disperser solvent was unnecessary. The extraction solvent was collected conveniently with an external magnetic field placed outside the extraction container after dispersing. Then, the magnetic nanoparticles were easily removed by adding precipitation reagent under the magnetic field. In order to evaluate the validity of this method, ten organochlorine pesticides (OCPs) were chosen as the analytes. Parameters influencing the extraction efficiency such as extraction solvents, volume of extraction solvents, extraction time, and ionic strength were investigated and optimized. Under the optimized conditions, this method showed high extraction efficiency with low limits of detection of 1.8–8.4 ng L⁻¹, good linearity in the range of 0.05–10.00 μg L⁻¹ and the precisions were in the range of 1.3–9.6% (RSD, n = 5). Finally, this method was successfully applied in the determination of OCPs in real water samples.     

Electrochemically controlled self-assembled monolayers characterized with molecular and sub-molecular resolution

Self-assembled organization of functional molecules on solid surfaces has developed into a powerful and sophisticated tool for surface chemistry and nanotechnology. A number of reviews on the topic have been available since the mid 1990s. This perspective article aims to focus on recent development in the investigations of electronic structures and assembling dynamics of electrochemically controlled self-assembled monolayers (SAMs) of thiol containing molecules on gold surfaces. A brief introduction is first given and particularly illustrated by a Table summarizing the molecules studied, the surface lattice structures and the experimental operating conditions. This is followed by discussion of two major high-resolution experimental methods, scanning tunnelling microscopy (STM) and single-crystal electrochemistry. In Section 3, we briefly address choice of supporting electrolytes and substrate surfaces, and their effects on the SAM structures. Section 4 constitutes the major body of the article by offering some details of recent studies for the selected cases, including in situ monitoring of assembling dynamics, molecular electronic structures, and the key external factors determining the SAM packing. In Section 5, we give examples of what can be offered by theoretical computations for the detailed understanding of the SAM electronic structures revealed by STM images. A brief summary of the current applications of SAMs in wiring metalloproteins, design and fabrication of sensors, and single-molecule electronics is described in Section 6. In the final two sections (7 and 8), we discuss the current status in understanding of electronic structures and properties of SAMs in electrochemical environments and what could be expected for future perspectives.     

The dynamics of a novel method coupling high-performance liquid chromatography with resonance Rayleigh scattering

The dynamics of a novel method coupling high‐performance liquid chromatography (HPLC) with resonance Rayleigh scattering (RRS) is presented in the paper. The method was employed in the detection of fluoroquinolones (FQs) of urine samples from healthy human beings, by forming ion‐association complexes between the components separated from HPLC and [Ce(OH)₃]⁺ as the molecular recognition probe. The RRS signal was measured at λ_ex=λ_em=365 nm. It was applied to detect three FQs and obtained satisfactory results. The RRS spectral characteristics of the analytes and the kinetics of flow rate, proportion of organic phase, reaction time and the aggregation level of ion‐association complexes were investigated, which provided a new basis for the development of the hyphenated techniques. It was established that the presence of HPLC‐RRS would open up a new field in the determination of analytes in the absence of UV or fluorescence.     

Intermixed Adatom and Surface‐Bound Adsorbates in Regular Self‐Assembled Monolayers of Racemic 2‐Butanethiol on Au(111)

In situ scanning tunneling microscopy combined with density functional theory molecular dynamics simulations reveal a complex structure for the self‐assembled monolayer (SAM) of racemic 2‐butanethiol on Au(111) in aqueous solution. Six adsorbate molecules occupy a (10×√3)R30° cell organized as two RSAuSR adatom‐bound motifs plus two RS species bound directly to face‐centered‐cubic and hexagonally close‐packed sites. This is the first time that these competing head‐group arrangements have been observed in the same ordered SAM. Such unusual packing is favored as it facilitates SAMs with anomalously high coverage (30 %), much larger than that for enantiomerically resolved 2‐butanethiol or secondary‐branched butanethiol (25 %) and near that for linear‐chain 1‐butanethiol (33 %).     

LC Analysis of Kanamycin in Human Plasma, by Fluorescence Detection of the 9-Fluorenylmethyl Chloroformate Derivative

High-performance liquid chromatography with fluorescence detection has been used for simple and efficient analysis of the aminoglycoside kanamycin in human plasma. Kanamycin sulfate was derivatized with 9-fluorenylmethyl chloroformate (FMOC-Cl) in borate buffer (0.2 M, pH 8.5) for 30 min at 25 °C. The derivative was chromatographed on a 150 mm × 4.6 mm, 5-μm particle, C₈ column with 70% acetonitrile in water as mobile phase at a flow rate of 1.0 mL min^?1. Under these conditions the retention time of kanamycin-FMOC was 6.2 min. The fluorescence excitation and emission wavelengths were 268 and 318 nm, respectively. Recoveries ranging from 92.3 to 100.8% were obtained. The correlation coefficient was >0.999 over the range 0.1–4.0 μg mL^?1. The within-day precision of the method, as coefficient of variation, was 2.9–5.5% (n = 5). The kanamycin-FMOC derivative was stable in the reaction solution for 24 h at room temperature. Validation of the method is reported.     

Facile Synthesis via Electrospinning of a Tetraethoxysilane/Polyvinylpyrrolidone Sol and Characterization of Ultrafine Crystalline SiO2 Nanofibers

Silica nanofibers were developed by a combination of an electrospinning technique and the sol–gel method. In the process, tetraethoxysilane (TEOS), polyvinylpyrrolidone (PVP) and N, N-Dimethylformamide (DMF) were the components of the sol for the production of silica/PVP composite nanofibers by electrospinning. During a thermal treatment, PVP in the hybrid fibers was removed; in this way, we produced ultrafine crystalline silica nanofibers. Scanning electron microscopy, energy dispersive X-ray analyzer, X-ray diffraction, and Fourier transform infrared spectroscopy were used to characterize the nanofibers. These silica nanofibers should be potentially useful in catalyst support, adsorbent, energy storage, and gas storage applications.     

二苯氨基脲比色法测定岩石中的微量铬

采用二苯氨基脲比色法测定岩石中的铬(Ⅵ),相对误差不大于4.0％,处理成溶液后的检出限为1.62×10~(-7)g/mL。