Thermal analysis applied to the characterization of degradation in soil of polylactide: I. Calorimetric and viscoelastic analyses

An accelerated soil burial test has been performed on a commercial polylactide (PLA) for simulating non-controlled disposal. Degradation in soil promotes physical and chemical changes in polylactide properties, which can be characterized by Thermal Analysis techniques. Physical changes occurred in polylactide due to the degradation in soil were evaluated by correlating their calorimetric and viscoelastic properties. It is highly remarkable that each calorimetric scan offers specific and enlightening information. Degradation in soil affects the polylactide chains reorganization. A multimodal melting behavior is observed for buried PLA, degradation in soil also promotes the enlarging the lamellar thickness distribution of the population with bigger average size. Morphological changes due to degradation in soil lead to an increase in the free volume of the polylactide chains in the amorphous phase that highly affected the bulk properties. Thermal Analysis techniques provide reliable indicators of the degradation stage of polylactide induced by degradation in soil, as corroborated by molecular weight analysis.     

On‐line flow‐through extraction–preconcentration‐large volume injection‐RP LC for trace determination of pyrethroids in Slovak soil

A rapid micro‐analytical multiresidue method was developed for analysis of pyrethroids (kadethrin K, cypermethrin C and permethrin P) in soil micro‐sample (200 mg). It uses on‐line flow‐through extraction of soil micro‐samples (packed into a short glass column) with a methanol‐aqueous citric acid buffer mixture, successive on‐line SPE preconcentration of analytes from the extract and on‐line RP‐HPLC analysis with UV photometric detection. The separation of pyrethroids is performed on a Purospher RP‐18e column with methanol/water as mobile phase. Effects of sorbent placed at the bottom of a short column holding the soil sample and different kinds of on‐line SPE columns were tested. Besides, the influence of volume of the effluent on the pyrethroids recovery was also studied. Calibration curves were linear over the range assayed from 0.01 to 0.2 μg/mL with correlation coefficients of linear regression (least‐squares method) in the range 0.998–0.999. Recovery studies were carried out at 0.25–1.00 μg/g dry soil fortification level and obtained recoveries were for K 81–84%, C 56–59% and for P 58–63%. Achieved LOD (confidence band) of studied pyrethroids were for large‐volume injection (1 mL) 4.5 ng K, 3.7 ng C, 3.6 ng P or 27 ng/g K, 32 ng/g C and 29 ng/g P in dry soil “solid sampling HPLC”.     

The carbon versus mass diagram to visualize and exploit FTICR‐MS data of natural organic matter

A two‐dimensional diagram is proposed, in which the carbon number of each formula is plotted against its nominal mass, to visualize large sets of molecular formula data that can be derived from data generated by ultrahigh‐resolution Fourier transform ion cyclotron resonance‐MS. In such a carbon versus mass (CvM) diagram, each formula (C_cH_hO_o) is unambiguously described by c, its (nominal) mass and the parameter i = c + o. Calculations of chemically allowable formulas illustrate that organic molecules occupy only certain spaces in such a diagram. The extension of these spaces increases with molecular mass in x‐direction (hydrogenation) and y‐direction (oxygenation). The data sets of molecules determined in natural organic matter(NOM) occupy only a certain range of the allowable space. The intensity of the mass spectrometric signals can be included as the third dimension into a CvM diagram. Separate CvM diagrams can be plotted for NOM molecules that include different heteroatoms. The benefits of the CvM diagram are illustrated by application onto data sets of fulvic acids from riverine and marine origin, of secondary organic aerosol, including organosulfates and organonitrates, as well as of ozonation of fulvic acids. The CvM diagram is a useful tool to visualize the elemental regularities in NOM isolates as well as the differences between isolates. It may also be applicable to large sets of molecular formula data generated in other disciplines such as petroleum biogeochemistry or metabolomics. Copyright © 2010 John Wiley & Sons, Ltd.     

气相色谱法测定茶叶及土壤中的高效氯氟氰菊酯残留量

建立了气相色谱测定茶叶及土壤中高效氯氟氰菊酯残留量的分析方法。茶叶和土壤样品用正己烷提取,毛细管柱分离,气相色谱-电子捕获检测器(GC-ECD)检测。结果表明: 在高效氯氟氰菊酯添加量为0.02～2.00 mg/kg范围内,高效氯氟氰菊酯在鲜茶叶和土壤中的平均添加回收率分别为89.0%～94.1%和89.8%～94.7%,相对标准偏差(RSD, n=5)分别为3.0%～4.9%和2.5%～4.2%,方法的最低检出限(S/N=3)为0.002 mg/kg。采用该方法测定2.5%高效氯氟氰菊酯微乳剂在湖南长沙茶叶及土壤中的消解动态,其符合一级动力学消解模式,消解方程分别为y=3.1996e-0.3394x和y=0.1224e-0.1036x,相关系数分别为0.9956和0.9247。在茶叶中的半衰期为2.04 d,在土壤中的半衰期为6.69 d。该方法为湖南长沙地区茶叶种植科学合理地使用杀虫剂高效氯氟氰菊酯提供了依据。     

原子吸收和原子荧光光谱法测定茶园土壤中的微量元素

采用微波消解-火焰原子吸收和原子荧光光谱法同时测定了贵州梵净山茶园土壤中14种微量元素含量,方法简单、准确、迅速,有助于全面、迅速地了解茶园土壤中微量元素的含量,对于特色茶叶品质鉴定和指导合理科学栽培茶树等方面有重要意义.     

冲击载荷下土的动态力学性能研究

 利用分离式霍普金森压杆（Split Hopkinson Pressure Bar,SHPB）技术,研究了土体在不同应变率条件下的冲击动态力学性能,发现土体有明显的应变率效应,与静载相比,冲击载荷下土的动强度和动模量均有很大的提高。根据实验曲线的特征,以一根线性弹簧和两个不同松弛时间的Maxwell体并联的粘弹性模型来表达土体的损伤型粘弹性本构模型,两个Maxwell体分别表示土体的低应变率响应和高应变率响应,模型的数值拟合曲线与实测动态本构曲线具有较好的一致性。拟合参数表明,土体对低应变率的响应与混凝土相同,对高应变率的敏感性远远高于混凝土。     

激光烧蚀脉冲放电激发的土壤等离子体电子数密度和温度的研究

以激光烧蚀快脉冲放电激发土壤为例,研究了激光烧蚀快脉冲放电等离子体技术产生的土壤等离子体的电子数密度和温度。根据实验测得的Si原子和离子谱线的强度和萨哈玻尔兹曼方程,计算了等离子体的电子温度,并从分析Si I 250.69nm谱线的斯塔克展宽中导出了等离子体的电子数密度。与使用同样激光能量激发的激光等离子体相比,激光烧蚀快脉冲放电激发等离子体的电子数密度和温度都明显增加,与观察到的光谱信号强度是一致的。     

土壤重金属铬元素的激光诱导击穿光谱定量分析研究

利用Nd ∶YAG脉冲激光器(波长:1064 nm)作为光源,在实验室自然大气环境下诱导产生土壤激光等离子体,通过等离子体原子发射光谱法定量分析了国家标准土壤样品中元素Cr的含量.实验上研究了在最佳实验条件下土壤中Cr的LIBS分析谱线,测定了Cr元素的定标曲线.实验结果表明,Cr元素浓度在(60—400)×10^-6范围内,元素含量与光谱线强度之间有较好的线性关系;元素Cr浓度分析测量的相对标准偏差(RSD)为7.89%,定量分析结果与标准值的相对偏差为5.3%,Cr元素的检测限为1 关键词： 土壤污染 定量分析 激光诱导击穿光谱 定标曲线     

酸性红黄壤土上大麦遗传改良研究

本文报道了酸性红黄壤土上大麦遗传改良研究结果:(1)采用酸铝营养液培养幼苗的方法鉴定了我国3871份大麦品种的耐酸铝性，得到一级耐性材料315份，占鉴定总数的8.13劣，(2)相关通径分析表明，酸性红黄壤土上大麦单株籽粒产量损失起主要作用的是有效分菜数下降(P = 0. 7324 )、每穗实粒数减少(P = 0 . 5923 )和千粒重降低(P = 0.5877),由此可见，这是在红黄壤土田间条件下选择耐酸铝性大麦的三个主要选择指标;(3)发现大麦耐酸铝性基因遗传方式除单基因遗传方式外，尚有多基因控制的表现数量性状遗传方式;'(4)从对酸铝性表现敏感的大麦品种“早熟3一号”的花药、幼胚等外植体诱导出的愈伤组织，通过离体细胞突变体筛选，得到了“耐性细胞系”.以上结果表明，通过耐酸铝性遗传改良培育出适应酸性红黄壤土种植的大麦新品种是可行的，亦为开发利用红黄壤土地资源补充了另一条有效途径.     

Dynamics of digging in wet soil

Numerous animals live in, and locomote through, subsea soils. To move in a medium dominated by frictional interactions, many of these animals have adopted unique burrowing strategies. This paper presents a burrowing model inspired by the Atlantic razor clam (Ensis directus), which uses deformations of its body to cyclically loosen and re-pack the surrounding soil in order to locally manipulate burrowing drag. The model reveals how an anisotropic body - composed of a cylinder and sphere varying sinusoidally in size and relative displacement - achieves unidirectional motion through a medium with variable frictional properties. This net displacement is attained even though the body kinematics are reciprocal and inertia of both the model organism and the surrounding medium are negligible. Our results indicate that body aspect ratio has a strong effect on burrowing velocity and efficiency, with a well-defined maximum for given kinematics and soil material properties.