HPLC—UV determination of pesticide residues at 0.01 ppm in apple and pear pulp used for baby food

Two distinct methods are described for determination of residues of ethiofencarb and triforine, and of diflubenzuron, teflubenzuron, and triflumuron at the 0.01 ppm level in apple and pear pulp used for baby food;recoveries are above 50%. Diflubenzuron, teflubenzuron, and triflumuron are extracted with a 1:1 mixture of dichloromethane and acetone, and the extracts are cleaned by SPE using C₁₈ as stationary phase and methanol as mobile phase. Ethiofencarb and triforine are extracted with dichloromethane, and the extracts cleaned using the same stationary phase but a 1:1 mixture of acetonitrile and water as mobile phase. Analysis of both groups of pesticides is by isocratic HPLC—UV at 210 nm using an RP-18 column and acetonitrile-water as mobile phase.     

Isolation and Identification of Residual Chromophores in Cellulosic Materials

A general procedure was developed for the isolation of residual chromophores in or on cellulosic material, which were hitherto inaccessible to structure elucidation due to their extremely low content in the ppb concentration scale. It is applicable to cellulosic pulp, cellulosic fibers (viscose, Lyocell) and cellulose derivatives (acetate, carbonyl-labeled cellulose) as well. The chromophore identification comprises treatment of the cellulosic material with boron trifluoride – acetic acid complex (BF₃*2HOAc) containing sulfite, chromatographic separation of the resulting chromophore-containing mixture, and structure determination of the main constituents by NMR / MS and comparison to authentic samples. Both adsorbed and covalently bound aromatic and quinoid compounds are selectively released by the treatment. Covalent ester, ether and secondary alkyl links between chromophore and cellulose are broken. Two cellulosic example substrates have been analyzed for their chromophore content: Lyocell fibers and non-bleached viscose fibers, and up to eleven chromophores per sample have been identified.     

昆虫自由飞行时翅膀攻角的光学测量

昆虫运动空气动力学研究需要测量昆虫运动的多种参数。其中 ,翅膀攻角是主要参数 ,是流体分析时主要的边界条件之一。由于昆虫的运动参数的测量同一般的测量相比具有一些特殊要求 ,它要求一定是非接触测量 ,因此成功的测量方法大都集中在光学测量方法上。本文以近年来有关昆虫自由飞行的实验为基础 ,着重介绍几种比较有特色的翅膀攻角的光学测量方法     

The influence of hemicellulose on fibril aggregation of kraft pulp fibres as revealed by FE-SEM and CP/MAS 13C-NMR

Three Norway spruce pulps were produced using different kraft pulping methods, in order to obtain large differences in cellulose and hemicellulose proportions at a similar lignin content. The hemicellulose content in the three pulps varied between 10% and 22%. The aim of the study was to evaluate the influence of cellulose and hemicellulose on fibre ultrastructure and correlate this with the differences observed in the mechanical properties between the pulps. The ultrastructure of the pulp fibres were studied using Field Emission Scanning Electron Microscopy (FE-SEM) and Solid-State Cross Polarisation Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance (CP/MAS ¹³C-NMR) in combination with spectral fitting. CP/MAS ¹³C-NMR measured the average bulk properties of the pulp fibres, while FE-SEM allowed for observations on the ultrastructure of fibre surfaces. The ultrastructure of the fibres varied with varying hemicellulose content. The pulp with a high hemicellulose content had a porous surface structure. In fibres with a low hemicellulose content, the fibril aggregates (macrofibrils) formed a much more compact surface structure. With CP/MAS ¹³C-NMR this change was reflected by an increase in average fibril aggregate width with decreasing hemicellulose content. Results from FE-SEM and CP/MAS ¹³C-NMR correlated well. The changes recorded in ultrastructure may explain the very different mechanical properties reported previously for pulps with different hemicellulose content.     

Properties and treatments of pulps from recycled paper. Part II. Surface properties and crystallinity of fibers and fines

Surface properties of bleached kraft pulps were evaluated before and after recycling, and after a series of chemical treatments designed to improve and/or modify the pulp characteristics. The surface free energy characteristics of the pulps were determined using the Wilhelmy technique, and ESCA and ATR-FTIR methods were used to evaluate the chemical composition of the surfaces of the pulp fibers. In general rather small changes were noted at the fiber surfaces with recycling and chemical treatment. Recycling tended to increase the acid component and decrease the base component of the surface free energy of the pulps. This could result from exposure of carboxyl groups from hemicelluloses and/or from oxidized layers from the bleaching process. ESCA analyses also indicated increased carboxyl concentration at the surfaces of the recycled fibers. Although treatment with aqueous bases and organic solvents tended to increase the hydroxyl content on the surface of recycled pulps, the chemical treatments were not beneficial to pulp quality. AFM and SEM of fiber and fine surfaces of kraft pulps revealed that the fines fraction was altered to a much greater extent with recycling. Although recycled fibers appeared to have improved wettability, these small changes in the surface characteristics do not appear to play the dominant role in the characteristics of recycled pulps. Recycling did not change the crystallinity of whole pulps, but it increased the crystallinity of the fines fraction. The increase in the crystallinity of the fines fraction and the reduction in the water retention value (WRV) and the bulk carboxyl content (xylan) of the recycled pulps, as noted in Part I of this paper, appear to play the predominant role in determining the characteristics of recycled pulps. It appears that the loss of the hemicelluloses in the bulk of the fiber with recycling is much more important for internal fibrillation than the apparent small increase of hemicelluloses at the surface of recycled fibers.     

昆虫运动机理的研究

昆虫运动机理研究是一门交叉学科的前沿基础研究。旨在完善现有的空气动力学理论,为微机械设计寻找新思想、新概念。本文重点介绍目前在昆虫运动参数测量中的一些关键问题和研究进展情况,并对如何分析这些参数进行一些简单说明     

纸浆卡伯值的在线测量数学模型

从Kubelka-Munk基本方程和纸浆中残留木素的光谱特性出发推导出纸浆漫反射理论模型,进而根据纸浆残余木素与纸浆卡伯值的本质关系推导出在线实时测量纸浆卡伯值的理论模型.根据纸浆中残留木素的光谱吸收特性,选择F390,F560和F840为自变量,建立了"三波长"纸浆卡伯值光谱测量简化模型.该模型结构简单,物理意义清晰,能够揭示模型自变量与卡伯值之间的线性关系.由于从机理模型变为简化模型经过了多次线性近似和简化,造成了纸浆卡伯值与反射光谱间的非线性信息缺失.为此,结合纸浆卡伯值光谱测量简化模型和自适应神经模糊推理系统(ANFIS),建立了纸浆卡伯值在线光谱测量的融合模型,经过样本训练后,融合模型预测结果稳定,精度高.     

Desorption of Coffee Pulp Used as an Adsorbent Material for Cr(III and VI) Ions in Synthetic Wastewater: A Preliminary Study

Some of the diverse agro-industrial waste generated in primary or secondary stages have proved to be promising biomaterials for treating aqueous effluents contaminated, in this case, with heavy metals. Therefore, it is necessary to know their optimal operating conditions and the regeneration or reusability of the solid by-product, an aspect related to desorption. Considering the above, this article presents the findings of a preliminary study related to the desorption process of coffee pulp without physicochemical modification (Castilla variety), an agricultural waste used as a sorbent of Cr(III and VI) ions in synthetic wastewater. The desorption efficiency of four eluting agents at defined concentrations (0.10M)—HC1, HNO₃, H₂SO₄, and EDTA—was evaluated in a time interval of 1 to 9 days. Likewise, the proposals for the sorption and/or desorption mechanisms proposed and reported in the literature with respect to the use of biosorbents derived from the coffee crop are presented. With respect to the results, the coffee pulp used in previous studies of the adsorption of chromium species mentioned (optimal conditions in synthetic water of particle size 180 μm, dose 20 g·L⁻¹, agitation 100 RPM, room temperature, time of 90 to 105 min) showed efficiencies in the removal of Cr(III) and Cr(VI) of 93.26% and 74.80%, respectively. Regarding the extracting substances used, H₂SO₄ 0.10 M was the one that presented the highest desorption percentage in both chromic species, with a desorption of 45.75% Cr(VI) and 66.84% Cr(III) in periods of 5 and 9 days, respectively, with agitation of 100 RPM and room temperature. Finally, the dissemination of preliminary results on the desorption of coffee pulp contaminated with chromic species without physicochemical modification is novel in this study, as similar work with this specific material has not yet been reported in the literature. On the other hand, the limitations of the study and future research are related to the evaluation at different concentrations and of other extractor solutions that allow improving the efficiency of desorption of these chemical species in a shorter time from the coffee pulp (with and without modification) as well as the reuse cycles. As a result, the desorption of coffee pulp used as an adsorbent material in real water could help researchers identify the possible interfering factors that affect the process (foreign anions and cations, organic matter, environmental conditions, among others).     

黑液除硅的模型试验

根据三因子二次回归正交设计试验,建立了草浆黑液的除硅模型,使用所筛选的除硅剂处理黑液,验证了模型,得到有用结论。     

Characterisation of the undissolved residuals ID CMC-solutions

The undissolved fibre and gel residuals that had not completely reacted to form fully dissolved carboxymethyl cellulose (CMC) ID the production of CMC were studied to clarify the reactivity of wood components ID the pulp. The undissolved residuals, the pulp and the CMC were therefore analysed on the fibre level, the cell-wall level and the chemical composition level. The results may be interpreted as indicating that the presence of undissolved residuals ID the CMC was not due to any chemical difference. The undissolved residuals were shown to consist mainly of swollen cell wall parts and some whole wood cells, mainly thick-walled compression wood and summerwood cells. They react more slowly ID the mercerisation and etherification, probably because of a greater diffusion resistance due to their larger dimensions or to a more dense structure. These cells are assumed to be less accessible for chemical penetration, but they may also contain supramolecular structures that slow down the CMC reaction.