Electrocatalytic oxidation of formaldehyde and methanol on Ni(OH)2/Ni electrode

A nickel hydroxide-modified nickel electrode (Ni(OH)₂/Ni) was successfully prepared by the cyclic voltammetry (CV) method and the electrocatalytic properties of the electrode for formaldehyde and methanol oxidation have been investigated respectively. The Ni(OH)₂/Ni electrode exhibits high electrocatalytic activity in the reaction. A new method has been developed for formaldehyde determination at the nickel hydroxide-modified nickel electrode and the experimental parameters were optimized. The oxidation peak current is linearly proportional to the concentration of formaldehyde in the range of 7.0 × 10^?5 to 1.6 × 10^?2 M with a detection limit of 2.0 × 10^?5 M. Recoveries of artificial samples are between 93.3 and 103.5%. The effect of scan rate and methanol concentration on the electrochemical behavior of methanol were investigated respectively.     

氢化物发生–原子荧光光度法测定食品和食品添加剂中的砷、汞和铅

建立氢化物发生–原子荧光光度法测定食品和食品添加剂中砷、汞和铅元素的方法。对茶叶、方便面、精料与二氧化硅样品的前处理方法进行了研究,讨论了酸介质与酸度、还原剂浓度、铁氰化钾与草酸浓度等因素对样品测定的影响。当还原剂质量浓度为20 g/L、载流酸度为5%、铁氰化钾和草酸质量浓度分别为4 g/L和2 g/L时,砷、汞和铅的方法检出限分别为0.024,0.008,0.066μg/L,方法的回收率为85%~105%,测量结果的相对标准偏差分别为0.7%,0.7%,1.8%。该方法简便、快速、结果准确可靠,能满足食品和食品添加剂中砷、汞、铅的测定。     

Catalytic effect analysis of metallic additives on light crude oil by TG and DSC tests

This research aimed at the investigation of the effect of different metallic additive on the combustion and kinetic behavior of crude oil. For this purpose, the thermal behavior of the oil-only and oil–metallic salts mixtures were studies by the thermogravimetry (TG)/derivative thermogravimetry and differential scanning calorimetry (DSC) on heating rate at 10 °C min^?1. The result shows that Dagang crude oil exhibited apparent low temperature oxidation (LTO), fuel deposition, and high temperature oxidation processes. With the addition of metallic salts, the LTO process has been shortened and samples added CuSO₄, CrCl₃·6H₂O, and AlCl₃·6H₂O achieved a much lower peak temperature than that of oil. Based on the Arrhenius model, metallic additives were proven to have obvious influence on the combustion activation energy. And, by comprehensive analysis of TG/DSC profile and activation energy, ZnSO₄ exhibited a positive influence on light crude oil combustion during the high pressure air injection process.     

Electrochemical sensor based on a carbon nanotube-modified imprinted sol–gel for selective and sensitive determination of ß2-agonists

We describe a molecularly imprinted electrochemical sensor for selective and sensitive determination of β₂-agonists. It is making use of a combination of single-wall carbon nanotubes (SWNTs) with a molecularly imprinted sol–gel. The SWNTs were introduced in order to enhance electron transport and sensitivity. The imprinted sol–gel film with its specific binding sites acts as a selective recognition element and as a preconcentrator for β₂-agonists. The morphology of the imprinted film was characterized by scanning electron microscopy. The optimized sensor displays high sensitivity and excellent selectivity for the β₂-agonists as shown for their determination in human serum samples.

Study of internal ring rotation and molecular reorientation in the liquid crystal 5O.7 by deuterium N.M.R. spectroscopy

Abstract

The spectral densities of motion were determined by deuterium N.M.R. relaxation measurements in the nematic, smectic A and smectic C phases of 4-n-pentyloxybenzylidene-d ₁-4′-heptylaniline and 4-n-pentyloxybenzylidene-4′-heptylaniline-2,3,5,6-d ₄. By examining two atomic sites on a 5O.7 molecule, we were able to gain information on the reorientation motion and internal rotation of the aniline ring. It was also found that director fluctuations make some contribution to the spectral density J ₁ (ω). We use the superimposed rotations model to account for the internal ring motion and the small step rotational diffusion model for the molecular reorientation. The derived rotational diffusion constants for the spinning and tumbling motions appear to give physically plausible activation energies in the mesophases of 5O.7.     

Multi-residue determination of plant growth regulators in apples and tomatoes by liquid chromatography/tandem mass spectrometry

A sensitive and rapid multi-residue analytical method for plant growth regulators (PGRs) (i.e., chlormequat, mepiquat, paclobutrazol, uniconazole, ethephon and flumetralin) in apples and tomatoes was developed using high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS). A homogenised sample was extracted with a mixture of methanol/water (90:10, v/v) and adjusted to pH <3 with formic acid. Primary secondary amine (PSA) adsorbent was used to clean up the sample. The determination was performed using electrospray ionisation (ESI) and a triple quadrupole (QqQ) analyser. Under the optimised method, the results showed that, except for ethephon, the recoveries were 81.8-98.1% in apples and tomatoes at the spiked concentrations of 0.005 to 2 mg/kg, with relative standard deviations (RSDs) of less than 11.7%. The limits of quantification (LOQs) were lower than their maximum residue limits (MRLs). The procedure was concluded as a practical method to determine the PGR residues in fruit and vegetables and is also suitable for the simultaneous analysis of the amounts of samples for routine monitoring. The analytical method described herein demonstrates a strong potential for its application in the field of PGR multi-residue analysis to help assure food safety.     

Surface structure and catalytic properties of MoO3/CeO2 and CuO/MoO3/CeO2

XRD, LRS, TPR and in situ NH(3) adsorption FT-IR were used to investigate the dispersion state of the copper oxide and molybdena species of MoO(3)/CeO(2) and CuO/MoO(3)/CeO(2) catalysts as well as their surface acidity. The results showed that the molybdena monolayer modification promoted the dispersion of CuO due to the formation of new tetrahedral vacancies. Meanwhile, CuO changed the structure of molybdenum species and then influenced the surface acidity of the samples. A detail discussion about the possible model of the surface structure of the catalyst was presented. In addition, combining with the in situ NH(3) adsorption FT-IR, the relationships between the activities for 'NO + NH(3) + O(2)' reaction and surface acid properties (Br?nsted and Lewis acid sites) of the catalysts were discussed.