Simultaneous Analysis of Hexaconazole, Myclobutanil, and Tebuconazole Residues in Apples and Soil by SPE Clean-Up and GC with Nitrogen–Phosphorus Detection

A facile and sensitive method utilizing capillary gas chromatography with nitrogen phosphorus detection (GC–NPD) has been developed and validated for simultaneous analysis of hexaconazole, myclobutanil, and tebuconazole, three broad-spectrum systemic fungicides, in apples and soil. Two samples were fortified with the three pesticides and subjected to ultrasonic extraction, followed by solid-phase extraction (SPE) to remove coextractives, before analysis by GC–NPD. SPE procedures were performed on PSA cartridges (500 mg, 3 mL), the analytes being eluted with n-hexane–acetone (9:1 v/v, 2 mL). Recovery of three pesticides from the fortified apple and soil samples ranged from 94.5 to 107.3% with relative standard deviations less than 9.7% at the three spike levels (0.01, 0.1, and 0.5 mg kg^?1). Limits of quantification of the method for apple and soil were 0.01 mg kg^?1, sufficiently below the maximum residue limits. Direct confirmation of the analytes in samples was achieved by gas chromatography–mass spectrometry (GC–MS).     

Step‐Mediated Anisotropic Adsorption and Condensation of tert‐Butylamine on Cu(111)

Scanning tunneling microscopy (STM) combined with density functional theory (DFT) calculations were applied in studying the anisotropic adsorption and condensation of tert‐butylamine (t‐BA) molecules in the vicinity of the steps on the Cu(111) surface. The preferential adsorption at the upper step edges and uneven distribution of t‐BA in the vicinity of the steps illustrate the asymmetric electronic structure of the surface steps. Our observation demonstrates that the adsorption and diffusion of a polar molecule would be significantly mediated by steps on metal surfaces due to the molecule–step interaction and the intermolecular interactions.     

UV and visible light controllable depletion zone of ZnO-polyaniline p-n junction and its application in a photoresponsive sensor

In this communication, we report that the depletion zone thickness of the p-n junction between an n-type ZnO and a p-type polyaniline could be controlled by UV and visible light illumination. Based on this princile, photoresponsive sensors were constructed by combining polyaniline thin film and ZnO nanorods. Different from pure ZnO nanomaterials whose conductivity increases when they are exposed to UV illumination, the conductivity of the photoresponsive sensor studied in this communication decreased when the UV light was turned on. The surface modification of ZnO could switch the wavelength of the response light from UV to visible light.     

Development of single‐drop microextraction and simultaneous derivatization followed by GC‐MS for the determination of aliphatic amines in tobacco

In this work, for the first time, headspace (HS) single‐drop microextraction and simultaneous derivatization followed by GC‐MS was developed to determine the aliphatic amines in tobacco samples. In the HS extraction procedure, the mixture of derivatization reagent and organic solvent was employed as the extraction solvent for HS single‐drop microextraction and in situ derivatization of aliphatic amine in the samples. Fast extraction and simultaneous derivatization of the analytes were performed in a single step, and the obtained derivatives in the microdrop extraction solvent were analyzed by GC‐MS. The optimized experiment conditions were: sample preparation temperature of 80°C and time of 30 min, HS extraction solvent (the mixture of benzyl alcohol and 2,3,4,5,6‐pentafluorobenzaldehyde) volume of 2.0 μL, extraction time of 90 s. With the optimal conditions, the method validations were also studied. The method has good linearity (R² more than 0.99), accepted precision (RSD less than 13%), good recovery (98–104%) and low limit of detection (0.11–0.97 μg/g). Finally, the proposed technique was successfully applied to the analyses of aliphatic amines in tobacco samples of seven different brands. It was further demonstrated that the proposed method offered a simple, low‐cost and reliable approach to determine aliphatic amines in tobacco samples.     

MEKC determination of IgG in human serum via a pH‐mediated acid stacking method

An on‐column preconcentration technique, pH‐mediated acid stacking, was used in this study to improve the sensitivity of MEKC‐UV analysis of IgG in human serum. Various parameters affecting pH‐mediated acid stacking were optimized systematically. To eliminate the matrix interferences of human serum and to combine the sample pretreatment procedure with the detection methodology, silica‐coated Fe₃O₄ magnetic nanoparticles modified with N‐(2‐aminoethyl)‐3‐aminopropyl‐trimethoxysilane were prepared and employed as solid phase extraction adsorbent to remove the abundant HSA from human serum. HSA was quantitatively removed by silica‐coated Fe₃O₄ magnetic nanoparticles modified with N‐(2‐aminoethyl)‐3‐aminopropyl‐trimethoxysilanes without retaining IgG at pH 9.3. Under the optimum conditions, the sensitivity of IgG was improved 40.3‐fold using a 100 s electrokinetic injection as compared with a 6 s hydrodynamic injection. The detection limit of IgG was found to be 0.1 mg/L, and the proposed method was successfully applied for the determination of IgG in human serum with satisfactory results.     

Synthesis,characterization, and drug release behaviors of a novel thermo‐sensitive poly(N‐acryloylglycinates)

In this study, a novel thermo‐sensitive poly(N‐acryloylglycinates) was prepared in order to get a potential drug release carrier. The corresponding monomers and the polymers were characterized with Fourier‐transform infrared (FTIR) and ¹H NMR. The thermo‐sensitivity of the poly(N‐acryloylglycinates) was evaluated by measuring their lower critical solution temperatures (LCST) in water, inorganic salt solution, and different pH solutions. The results indicated that poly(N‐acryloylglycine methyl ester) (NAGME) and poly(N‐acryloylglycine ethyl ester) (NAGEE) exhibit a reversible thermo‐sensibility in their aqueous solutions at 61.5 and 12.5°C, respectively. However, no thermo‐sensitive behavior of poly(N‐acryloylglycine propyl ester) (NAGPE) was found due to its over hydrophobicity. The swelling studies on hydrogels were carried out at different temperatures, in different pH, and inorganic salt solutions. The hydrogels showed a remarkable phase transition at about 35°C with changing temperature. The release rate of caffeine from the thermo‐sensitive hydrogel was apparently decreased as the crosslinker content increased and temperature decreased. Seventy five percent caffeine from the polymeric hydrogel with 5% NMBA (N, N‐methylenebis(acrylamide)) was released at room temperature within 240 min, whereas 95.4% caffeine diffused into the medium at 37°C. Copyright © 2009 John Wiley & Sons, Ltd.     

Molecular modeling for the interaction between proteasome beta 5 subunit and organotin compounds

It has been reported that organotins can inhibit the proteasomal chymotrypsin-like activity and induce cell death, but the interaction mode of organotins with proteasome has not been well defined. In this study, the IC₅₀ of butyltins and phenyltins against the proteasomal activity and the nature of their inhibition were investigated. It was found that both mono- and di-organotins were weak, reversible inhibitors against the proteasome, while tributyltin and triphenyltin were potent, irreversible proteasome inhibitors. In silico studies using the reversible organotin proteasome inhibitors demonstrated a tight correlation of the estimated proteasomal inhibition constants (Ki) with the experimental IC₅₀ values for proteasome inhibition. Furthermore, the Sn atom in TBT and TPT was found susceptible to form a coordinate bond with Thr 1 O^γ of the β5 subunit, which may account for the irreversible proteasome inhibition. The computational docking approach well predicted the inhibition nature of organotins toward the proteasomal chymotrypsin-like activity. This predictive model might aid in understanding the cytotoxic behavior of similar organometallic compounds.     

Establishment of an immunoaffinity chromatography for simultaneously selective extraction of Sudan I, II, III and IV from food samples

The establishment of an immunoaffinity chromatography (IAC) for simultaneously selective extraction of four illegal colorants Sudan dyes (Sudan I, II, II and IV) from food samples was described. The IAC column was constructed by covalently coupling monoclonal antibody (mAb) against Sudan I to CNBr-activated Sepharose 4B and packed into a common solid phase extraction (SPE) cartridge. It was observed that IAC column was able to separately capture Sudan I, II, III and IV with maximum capacity of 295, 156, 184 and 173ng, respectively. The extraction conditions including loading, washing and eluting solutions were carefully optimized. Under optimal conditions, the extraction recoveries of the IAC column for Sudan I-IV at two different spiked concentrations were within 95.3-106.9%. After 50 times repeated usage, 64% of the maximum capacity was still remained. Six food samples randomly collected from local supermarket without spiking Sudan dyes were extracted with IAC column and detected by high performance liquid chromatography (HPLC). It was found that there was no detectable Sudan II, III and IV in all six food samples, but Sudan I with the content of 2.7-134.5ngg(-1) was detected in three food samples. To further verify the extraction efficiency, other three negative samples were spiked with Sudan I-IV at the concentrations of 20ngg(-1) and 50ngg(-1), which were then extracted with IAC column. The extraction recoveries and relative standard deviation (RSD) were 68.6-96.0% and 4.8-15.2%, respectively, demonstrating the feasibility of the prepared IAC column for Sudan dyes extraction.     

Combination synchronization of three classic chaotic systems using active backstepping design

In this paper, an active backstepping design is proposed to achieve combination synchronization between three different chaotic systems: Lorenz system, Chen's system, and Lu? system. The proposed method is a systematic design approach and consists in a recursive procedure that interlaces the choice of a Lyapunov function with the design of active control. Numerical simulations are shown to verify the feasibility and effectiveness of the proposed control technique.