Field‐amplified sample injection combined with capillary electrophoresis for the simultaneous determination of five chlorophenols in water samples

A sensitive method of CZE‐ultraviolet (UV) detection based on the on‐line preconcentration strategy of field‐amplified sample injection (FASI) was developed for the simultaneous determination of five kinds of chlorophenols (CPs) namely 4‐chlorophenol (4‐CP), 2‐chlorophenol (2‐CP), 2,4‐dichlorophenol (2,4‐DCP), 2,4,6‐trichlorophenol (2,4,6‐TCP), and 2,6‐dichlorophenol (2,6‐DCP) in water samples. Several parameters affecting CZE and FASI conditions were systematically investigated. Under the optimal conditions, sensitivity enhancement factors for 4‐CP, 2‐CP, 2,4‐DCP, 2,4,6‐TCP, and 2,6‐DCP were 9, 27, 35, 43, and 43 folds, respectively, compared with the direct CZE, and the baseline separation was achieved within 5 min. Then, the developed FASI‐CZE‐UV method was applied to tap and lake water samples for the five CPs determination. The LODs (S/N = 3) were 0.0018–0.019 µg/mL and 0.0089–0.029 µg/mL in tap water and lake water, respectively. The values of LOQs in tap water (0.006–0.0074 µg/mL) were much lower than the maximum permissible concentrations of 2,4,6‐TCP, 2,4‐DCP, and 2‐CP in drinking water stipulated by World Health Organization (WHO) namely 0.3, 0.04, and 0.01 µg/mL, respectively, and thereby the method was suitable to detect the CPs according to WHO guidelines. Furthermore, the method attained high recoveries in the range of 83.0–119.0% at three spiking levels of five CPs in the two types of water samples, with relative standard deviations of 0.37–8.58%. The developed method was proved to be a simple, sensitive, highly automated, and efficient alternative to CPs determination in real water samples.     

Fast quantification of cyclophosfamide and its N‐dechloroethylated metabolite 2‐dechloroethylcyclophosphamide in human plasma by UHPLC‐MS/MS

A rapid, novel and reliable UHPLC‐MS/MS method was developed and validated for simultaneous determination of cyclophosphamide (CP) and its dechloroethylated metabolite, 2‐dechloroethylcyclosphamide (2‐DCECP) in human plasma. The plasma samples were conducted by protein precipitation with 3‐fold acetonitrile, containing 0.1% formic acid. Mass spectrometric detection was performed using electrospray positive ionization with multiple reaction monitoring mode, using tinidazole as internal standard (IS). Chromatographic separation was performed on an Agilent poroshell 120 SB‐C₁₈ column (2.1 × 75 mm, 2.7 µm) using gradient elution of acetonitrile and 0.1% formic acid at a flow rate of 0.5 mL/min, the total run time was 2.5 min. The limit of quantification (LOQ) was 20 ng/mL for both CP and 2‐DCECP. Accuracies and precisions were <15% at LOQ and below 10% at quality control concentration levels. This UHPLC‐MS/MS method was successfully applied for the estimation of CP and 2‐DCECP in human plasma, which was also useful for clinical toxicology studies and therapeutic drug monitoring of CP. Copyright © 2014 John Wiley & Sons, Ltd.     

Controlled synthesis of responsive hydrogel nanostructures via microcontact printing and ATRP

Surfaces that are spatially functionalized with intelligent hydrogels, especially at the micro‐ and nanoscale, are of high interest in the diagnostic and therapeutic fields. Conventional methods of the semiconductor industry have been successfully employed for the patterning of hydrogels for various applications, but methods for fabricating precise 3 D patterns of hydrogels at the micro‐ and nanoscale over material surfaces remain limited. Herein, microcontact printing (µCP) followed by atom transfer radical polymerization (ATRP) was applied as a platform to synthesize temperature responsive poly(N‐isopropylacrylamide) hydrogels with varied network structures (e.g. different molecular weight crosslinkers) over gold surfaces. The XY control of the hydrogels was achieved using µCP, and the Z (thickness) control was achieved using ATRP. The controlled growth and the responsive behavior of hydrogels to temperature stimuli were characterized using Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM). The results demonstrate that this platform allows for the controlled growth of hydrogel nanostructures using the controlled ATRP mechanism. It is also shown that the molecular weight of the crosslinker affects the rate of hydrogel growth. These PNIPAAm‐based crosslinked hydrogel patterns were also demonstrated to have a temperature‐dependent swelling response. Using this technique, it is possible to synthesize responsive hydrogel patterns over various surfaces for potential applications in the biomedical field. Copyright © 2009 John Wiley & Sons, Ltd.     

Direct chiral resolution of cloquintocet-mexyl and its application to in vitro degradation combined with clodinafop-propargyl

A simple chiral high‐performance liquid chromatography (HPLC) method with ultraviolet (UV) detection was developed and validated for measuring Cloquintocet‐mexyl (ClM) enantiomers and clodinafop‐propargyl (CP) using cellulose tris‐(3,5‐dimethylphenylcarbamate) (CDMPC) as chiral stationary phase (CSP). The effects of mobile phase composition and column temperature on the ClM enantiomer separation were investigated. Good separation was achieved by using a mixture of n‐hexane and n‐propanol as mobile phase. Based on the chiral HPLC method, enantioselective quantitative determination analysis methods for this herbicide combined with CP in diluted plasma were developed and validated. The assay method was linear over a range of concentrations (0.5–100 µg/mL) in diluted plasma and the mean recovery was greater than 80% for both enantiomers and CP. The limits of quantification and detection for both ClM enantiomers and CP were 0.5 and 0.2 µg/mL, respectively. Intra‐ and interday relative standard deviations did not exceed 10% for three tested concentrations. The result suggested that the degradation of ClM enantiomers was stereoselective in rabbit plasma, and both rac‐ClM and CP degraded quickly in plasma, showing that the main existing forms with biological effect in animals are their metabolites. Copyright © 2011 John Wiley & Sons, Ltd.     

Coupling Proteins to Amine-terminated Magnetic Particles Activated with 1,4-Phenylene Diisothiocyanate

The homobifunctional crosslinker 1,4‐phenylene diisothiocyanate (PDC) was coupled to amine‐terminated magnetic particles, and human IgG, streptavidin, protein G and protein A were immobilized on the activated magnetic particles. The coupling of PDC to the amine‐terminated magnetic particles was completed in 10 min, and 1 mg of activated magnetic particles was able to immobilize 95 (g of protein G, 120 µg of protein A, 160 µg of streptavidin and 280 µg of IgG. Ultraviolet‐visible spectroscopy, FTIR spectroscopy and electron micrography were used to characterize the functional particles. The results indicated that PDC was successfully coupled to the surface of the amine‐terminated magnetic particles, and the proteins were effectively immobilized on their surface. The activity of protein G immobilized on the activated magnetic particles was confirmed by its ability to purify IgG from plasma.     

Two‐Photon Polymerization as a Tool for Studying 3D Printed Topography‐Induced Stem Cell Fate

Geometric topographies are known to influence cellular differentiation toward specific phenotypes, but to date the range of features and type of substrates that can be easily fabricated to study these interactions is somewhat limited. In this study, an emerging technology, two‐photon polymerization, is used to print topological patterns with varying feature‐size and thereby study their effect on cellular differentiation. This technique offers rapid manufacturing of topographical surfaces with good feature resolution for shapes smaller than 3 µm. Human‐induced pluripotent stem cells, when attached to these substrates or a non‐patterned control for 1 week, express an array of genetic markers that suggest their differentiation toward a heterogeneous population of multipotent progenitors from all three germ layers. Compared to the topographically smooth control, small features (1.6 µm) encourage differentiation toward ectoderm while large features (8 µm) inhibit self‐renewal. This study demonstrates the potential of using two‐photon polymerization to study and control stem cell fate as a function of substrate interactions. The ability to tailor and strategically design biomaterials in this way can enable more precise and efficient generation or maintenance of desired phenotypes in vitro and in vivo.     

Facile measurement of polymer film thickness ranging from nanometer to micrometer scale using atomic force microscopy

As many properties of polymer thin films critically depend on their thickness, a convenient and cost‐effective method for precise measurement of film thickness in a wide range is highly desirable. Here, we present a method which enables polymer film thickness, ranging from nanometer to micrometer scale, to be facilely determined by measuring the height of an artificially created film step on smooth substrates with atomic force microscopy (AFM). Three polymeric films (polystyrene, poly(methyl methacrylate) and poly(styrene–ethylene/butylene–styrene) films), spin‐coated on either mica or quartz substrate with thickness ranging from 5.7 nm to 4.4 µm, were employed to demonstrate the procedure and feasibility of our method. The proposed method is particularly suitable for thicker polymer films, thus complementing the traditional AFM ‘tip‐scratch’ method which is generally limited to polymer films of no more than 100 nm thickness. Copyright © 2010 John Wiley & Sons, Ltd.     

On‐line solid‐phase extraction coupled with liquid chromatography/electrospray ionization mass spectrometry for the determination of trace tributyltin and triphenyltin in water samples

On‐line solid‐phase extraction (SPE) for pre‐concentration and sample cleanup is one strategy to reduce matrix effects and to simultaneously improve detection sensitivity in liquid chromatography/mass spectrometry (LC/MS). This paper describes an on‐line SPE‐LC/MS method for the determination of tributyltin (TBT) and triphenyltin (TPhT) at trace levels in water samples. The direct coupling of an on‐line C₁₈ pre‐column to LC/MS was used to pre‐concentrate TBT and TPhT at trace levels from waters and to remove interfering matrix effects. Pre‐concentration was followed by separation of TBT and TPhT on a C₁₈ column using a mobile phase containing 0.1% (v/v) HCOOH/5 mM HCOONH₄ and methanol. While both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) can be interfaced with MS for the detection of TBT and TPhT, ESI‐MS was preferred for this application. The calibration curve for the targets was linear in the concentration range 0.1–30 µg L^?1. The detection limit (signal‐to‐noise (S/N) ratio = 3) was 0.02 µg L^?1 when 3.0 mL of sample was enriched on the C₁₈ pre‐column. The recoveries of TBT and TPhT in spiked waters were from 81.0 to 101.9%. The reproducibilities for the analysis of the standard mixture (10 µg L^?1) for TBT and TPhT were 13.1 and 5.0%, respectively. The developed method was an easy and fast way to analyze TBT and TPhT in water samples. Copyright © 2009 John Wiley & Sons, Ltd.     

Nanodroplets of polyisoprene fluid contained within poly(acrylic acid‐co‐acrylamide) shells

The preparation and characterization of macromolecular nanostructures possessing an amphiphilic core–shell morphology with a hydrophobic, fluidlike core domain with a low glass‐transition temperature are described. The nanostructures were prepared by the self‐assembly of polyisoprene‐b‐poly(acrylic acid) diblock copolymers into polymer micelles, followed by crosslinking of the hydrophilic shell layer via condensation between the acrylic acid functionalities and 2,2′‐(ethylenedioxy)bis(ethylamine), in the presence of 1‐(3′‐dimethylaminopropyl)‐3‐ethylcarbodiimide methiodide. The properties of the resulting shell‐crosslinked knedel‐like (SCK) nanoparticles were dependent on the microstructure and properties of the polyisoprene core domain. SCKs containing polyisoprene with a mixture of 3,4‐ and 1,2‐microstructures underwent little shape distortion upon adsorption from aqueous solutions onto mica or graphite. In contrast, when SCKs were composed of polyisoprene of predominantly cis‐1,4‐repeat units, the glass‐transition temperature was ?65 °C, and the nanospheres deformed to a large extent upon adsorption onto a hydrophilic substrate (mica). Adsorption onto graphite gave a less pronounced deformation, as determined by a combination of transmission electron microscopy and atomic force microscopy. Subsequent crosslinking of the core domain (in addition to the initial shell crosslinking) dramatically reduced the fluid nature and, therefore, reduced the SCK shape change. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1659–1668, 2003     

Ultrathin Covalently Bound Organic Layers on Mica: Formation of Atomically Flat Biofunctionalizable Surfaces

Mica is the substrate of choice for microscopic visualization of a wide variety of intricate nanostructures. Unfortunately, the lack of a facile strategy for its modification has prevented the on‐mica assembly of nanostructures. Herein, we disclose a convenient catechol‐based linker that enables various surface‐bound metal‐free click reactions, and an easy modification of mica with DNA nanostructures and a horseradish peroxidase mimicking hemin/G‐quadruplex DNAzyme.     

Application of a Deconvolutive Procedure to Analyze Several Chlorophenol Species in Natural Waters by Square‐Wave Voltammetry on the Boron‐Doped Diamond Electrode

Abstract

The anodic voltammetric behavior of 4‐chlorophenol (4‐CP) on a boron‐doped diamond electrode (BDD) in aqueous solution was studied by square‐wave voltammetry. After optimization of the experimental conditions, 4‐CP was determined in a Britton‐Robinson buffer solution with pH 6.0, prepared with pure water. Moreover, mixtures of some different chlorophenols were also investigated and an analytical method was developed for the simultaneous determination of these compounds in natural waters. The oxidation of 4‐CP on BDD was used for analytical purposes and quantification limits as low as 9.2 µg L^?1 were obtained. This result illustrates the advantage of using oxidation process currents on BDD electrodes as the analytical signal, even in contaminated matrices. In order to compare the results found here with the conventional methodology to determine chlorophenols, HPLC‐UV‐vis measurements were also performed and were in good agreement with the analytical values obtained by SWV.     

Gas chromatography–electron ionization–mass spectrometry quantitation of valproic acid and gabapentin,using dried plasma spots,for therapeutic drug monitoring in in‐home medical care

A simple and sensitive gas chromatography–electron ionization–mass spectrometry (GC‐EI‐MS) method using dried plasma spot testing cards was developed for determination of valproic acid and gabapentin concentrations in human plasma from patients receiving in‐home medical care. We have proposed that a simple, easy and dry sampling method is suitable for in‐home medical patients for therapeutic drug monitoring. Therefore, in the present study, we used recently developed commercially available easy handling cards: Whatman FTA DMPK‐A and Bond Elut DMS. In‐home medical care patients can collect plasma using these simple kits. The spots of plasma on the cards were extracted into methanol and then evaporated to dryness. The residues were trimethylsilylated using N‐methyl‐N‐trimethylsilyltrifluoroacetamide. For GC‐EI‐MS analysis, the calibration curves on both cards were linear from 10 to 200 µg/mL for valproic acid, and from 0.5 to 10 µg/mL for gabapentin. Intra‐ and interday precisions in plasma were both ≤13.0% (coefficient of variation), and the accuracy was between 87.9 and 112% for both cards within the calibration curves. The limits of quantification were 10 µg/mL for valproic acid and 0.5 µg/mL for gabapentin on both cards. We believe that the present method will be useful for in‐home medical care. Copyright © 2014 John Wiley & Sons, Ltd.     

A solid-phase bioreactor with continuous sample deposition for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

We report the development of a solid‐phase proteolytic digestion and continuous deposition microfluidic chip platform for low volume fraction collection and off‐line matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) mass spectrometry. Tryptic peptides were formed in an on‐chip bioreactor and continuously deposited onto a MALDI target plate using a motor‐driven xyz stage. The bioreactor consisted of a 4 cm × 200 µm × 50 µm microfluidic channel with covalently immobilized trypsin on an array of 50 µm diameter micropost structures with a 50 µm edge‐to‐edge inter‐post spacing. A 50 µm i.d. capillary tube was directly attached to the end of the bioreactor for continuous sample deposition. The MALDI target plate was modified by spin‐coating a nitrocellulose solution containing a MALDI matrix on the surface prior to effluent deposition. Protein molecular weight standards were used for evaluating the performance of the digestion and continuous deposition system. Serpentine sample traces 200 µm wide were obtained with a 30 fmol/mm quantity deposition rate and a 3.3 nL/mm volumetric deposition rate. Copyright © 2011 John Wiley & Sons, Ltd.     

Inhibition effect of cerium in hybrid sol–gel films on aluminium alloy AA2024

Aluminium alloys such as AA2024 are susceptible to severe corrosion attack in aggressive solutions (e.g. chlorides). Conversion coatings, like chromate, or rare earth conversion coatings are usually applied in order to improve corrosion behaviour of aluminium alloys. Methacrylate‐based hybrid films deposited with sol–gel technique might be an alternative to conversion coatings. Barrier properties, paint adhesion and possibly self‐healing ability are important aspects for replacement of chromate‐based pre‐treatments. This work evaluates the behaviour of cerium as corrosion inhibitor in methacrylate silane‐based hybrid films containing SiO₂ nano‐particles on AA2024. Hybrid films were deposited on aluminium alloy AA2024 by means of dip‐coating technique. Two different types of coating were applied: a non‐inhibited film consisting of two layers (non‐inhibited system) and a similar film doped with cerium nitrate in an intermediate layer (inhibited system). The film thickness was 5 µm for the non‐inhibited system and 8 µm for the inhibited system. Film morphology and composition were investigated by means of GDOES (glow discharge optical emission spectroscopy). Moreover, GDOES qualitative composition profiles were recorded in order to investigate Ce content in the hybrid films as a function of immersion time in 0.05 M NaCl solution. The electrochemical behaviour of the hybrid films was studied in the same electrolyte by means of EIS technique (electrochemical impedance spectroscopy). Electrochemical measurements provide evidence that the inhibited system containing cerium displays recovery of electrochemical properties. This behaviour is not observed for the non‐inhibited coating. GDOES measurements provide evidence that the behaviour of inhibited system can be related to migration of Ce species to the substrate/coating interface. Copyright © 2010 John Wiley & Sons, Ltd.     

Electroanalysis of Norepinephrine at Bare Gold Electrode Pure and Modified with Gold Nanoparticles and S‐Functionalized Self‐Assembled Layers in Aqueous Solution. Part II

Gold electrodes modified with S‐containing compounds and gold were used for determination of norepinephrine (NEP) in aqueous solution. A linear relationship between norepinephrine concentration and current response was obtained in the range of 0.1 µM to 600 µM with the detection limit ≤0.090 µM for the electrodes modified at 2D template and in the range of 0.1 µM to 700 µM with the detection limit ≤0.075 µM for the electrodes modified at 3D template. The results have shown that modified electrodes could clearly resolve the oxidation peaks of norepinephrine, ascorbic (AA) and uric acid (UA) with peak‐to‐peak separation enabling determination of NEP, AA and UA in the presence of each other.     

Synthesis of high‐molecular‐weight linear methacrylate copolymers with spiropyran side groups: Conformational changes of single molecules in solution and on surfaces

P(BMA‐co‐HEMA‐spiropyran) was synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization of butyl methacrylate (BMA) and 2‐(trimethylsilyloxy)‐ethyl methacrylate (HEMA‐TMS), removal of the TMS‐protective groups, and the polymer analogous esterification of the hydroxyethyl side chains with a spiropyran containing a carboxylic acid group. UV‐induced conformational changes of the synthesized macromolecules and low‐molecular‐weight spiropyran molecules were studied. Rate constants and half‐life times of the ring closure reaction from zwitterionic merocyanine to the spiropyran species were determined in the presence and absence of mica‐dispersed particles in toluene both with the free spiropyran and the polymer‐bound spiropyran. Scanning force microscopy was used to visualize the conformation of spiropyran‐decorated single macromolecular chains and agglomerated polymer‐bound merocyanine adsorbed on mica. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1274–1283, 2009     

Synthesis of 3,5-Dichloro-4-(1,1,2,2-tetrafluoroethoxy)phenyl Containing 1,2,3-Thiadiazole Derivatives via Ugi Reaction and Their Biological Activities

A series of novel 3,5‐dichloro‐4‐(1,1,2,2‐tetrafluoroethoxy)phenyl containing 4‐methyl‐1,2,3‐thiadiazole derivatives were designed and synthesized via Ugi reaction. Their structures were confirmed by IR, ¹H NMR, ¹³C NMR and high‐resolution mass spectroscopy. The preliminary bioassay results indicated that some title compounds had good fungicide activity at 50 µg/mL; most of the compounds presented a certain degree of direct inhibition activity, good inactivation and curative activity against tobacco mosaic virus at 500 µg/mL and 100 µg/mL; some compounds showed good larvicidal activity against Plutella xylostella L. at 200 µg/mL and excellent larvicidal activities against Culex pipiens pallens at 2 µg/mL.     

High‐resolution resist for screen printing: application to direct fabrication of Ag circuit

High‐resolution screen printing was devised. New resist formulation contains a base polymer, which consists of acid‐labile tetrahydropyranyl‐protected carboxylic acid, hydroxyl, and methacrylic functions. As crosslinkers, multifunctional acrylates were employed. Photoacid generators were used for pattern formation. A 10‐µm feature size of resist on a screen plate was obtained on irradiation at 365 nm and followed by development on a stainless steel screen. Post‐exposure curing improved the mechanical characteristics of the resist patterns. A 13‐µm feature size silver circuit was successfully printed on poly(ethylene terephthalate) film without defect. Copyright © 2011 John Wiley & Sons, Ltd.     

Direct detection of chlorpropham on potato skin using desorption electrospray ionization

Most pesticides, herbicides and other plant treatment agents are applied to the crop surface. Direct mass spectrometric methods, such as desorption electrospray ionization (DESI), offer new ways to analyze plant samples directly and rapidly. A strategy for the development and optimization of a DESI method for the direct determination of chemicals on complex surfaces is described. Chlorpropham (CP) was applied to potato surfaces as an example for a crop protection agent and analyzed using a self‐made DESI source. Aspects such as instrument selectivity, sensitivity and reproducibility were investigated. The MS⁴ fragmentation pattern of CP was analyzed to achieve the necessary detection selectivity, and is discussed in detail. Similar fragmentation was found in the ESI and DESI mass spectra, indicating that the mechanisms of ESI and DESI are closely related. A DESI method for semi‐quantification of CP on potatoes was developed. Detection limits of 6.5 µg/kg were found using MS/MS. The reproducibility, in the range of 12% (signal variation), appears to be sufficient for semi‐quantitative measurements. Copyright © 2013 John Wiley & Sons, Ltd.     

Crystallization of poly-p-oxybenzoate on mica

Thin film polymerization/crystallization of poly-4-oxybenzoate (P-4-OB) from melt or dilute solutions yields on mica cleavage surface an epitaxial overgrowth with crystal blocks oriented in 1 to 3 substrate directions rotated by 60°. The b and c crystal axes of P-4-OB lie in the mica cleavage plane, with the a axis being perpendicular to it. At higher polymerization temperatures a different type of P-4-OB orientation on mica was also observed: two P-4-temperatures a different type of P-4-OB orientation on mica was also observed: two P-4-OB phase I crystals, again with b- and c-axes lying parallel to mica cleavage plane, were oriented perpendicular to each other. There is a pronounced tendency of the relatively thick P-4-OB overgrowth to form complex crystal structures involving both phase I and II with different types of orientation on mica substrate. © 1996 John Wiley & Sons, Inc.