Simple spectrophotometric method for determination of phosphine residues in wheat

A method has been developed for determination of phosphine residues in wheat, based on the reaction of phosphine with silver nitrate in aqueous solution to form an egg-yellow chromophore with an absorption maximum at 400 nm. At this wavelength, there is a linear relationship between absorbance and concentration of phosphine in the range 10-100 ng/mL. Phosphine-fumigated wheat is soaked in a known volume of AgNO3 solution, and the absorbance of the filtrate is read against a blank at 400 nm. The method is sensitive, with lower detection and estimation limits of 0.008 and 0.01 micrograms PH3, respectively. Recovery of added phosphine from a closed system was 85-100%. Accuracy for this method has been compared with that for the gas chromatographic method.     

A novel method for quantification of 2-methyl-3-furanthiol and 2-furanmethanethiol in wines made from Vitis vinifera grape varieties

A rapid, easy method has been developed for isolating and quantifying 2-methyl-3-furanthiol (2M3F) in wines. Until now, it was not possible to quantify this highly odoriferous compound, with a smell reminiscent of cooked meat, in wine. The original aspect of this method is the specific release of volatile thiols using a cysteamine solution applied in reverse flow to sample percolation on the basis of a p-hydroxymercuribenzoate (pHMB)-volatile thiol conjugate formed by the direct addition of pHMB to 50 mL of wine. Purification of volatile thiols in wines is much faster and easier than our previous method. This method may also be used to assay 2-furanmethanethiol in wine. This thiol's strong aroma of roasted coffee has been shown to contribute to the "roast coffee" aroma of certain wines. Assaying 2M3F by this method showed that it was present in the wines analyzed (red and white Bordeaux, Loire Valley Sauvignon blanc, white Burgundy, and Champagne) at concentrations up to 100 ng/L, i.e., significantly above the olfactory perception threshold for this compound in model dilute alcohol solution.     

Colorimetric determination of hydroxyproline as measure of collagen content in meat and meat products: NMKL collaborative study

A colorimetric method for the determination of hydroxyproline as a measure of collagen in meat and meat products has been collaboratively studied in 18 laboratories. The method includes hydrolysis with sulfuric acid, oxidation with chloramine-T, and formation of a reddish purple complex with 4-dimethylaminobenzaldehyde. Five frozen and 3 freeze-dried samples were tested, ranging in content from 0.11 to 0.88% and from 0.39 to 4.0% hydroxyproline, respectively. The mean values of 2 identical samples were 0.245 and 0.251%. The average recovery from a spiked sample was 96.1%. The hydroxyproline content of a known sample (a mixture of 2 samples in the ratio 5:2) was calculated to 1.42%, which agrees well with the analytical result, 1.40%. In comparison with other collaborative studies, based on the ISO analytical method, the repeatability and reproducibility of this method agree well with the other results. This method was accepted as an official NMKL method by all national Committees, and has been adopted official first action by AOAC as an NMKL-AOAC method.     

贯流式水轮机转轮叶片的多学科优化设计

为了变革传统的转轮优化设计方法,在缩短转轮研发周期的同时能确保转轮安全、高效的运行,有必要开展转轮的多学科优化设计方法研究。该文基于多学科可行性优化策略(multidisciplinary feasible method,MDF)提出了一种能兼顾水力性能和强度应力的贯流式转轮叶片多学科优化设计方法。该方法以转轮叶片的几何形状参数作为优化变量,以转轮叶片的水力效率以及叶片上的最大静应力值作为优化目标,并通过MDF策略构建整个多学科优化求解系统,同时引入NSGA-II算法作为寻优算法开展了贯流式叶片的多学科优化设计。优化过程中,采用弱耦合方法完成每个优化个体的多学科性能分析以缩减整个优化流程的计算时间,提升了该方法的工程实用性。采用该方法对某电站的贯流式水轮机模型转轮进行优化,优化后水轮机的水力效率提高了0.3%,转轮叶片的最大应力值降低了16.3%,表明该方法是有效的,并具有实际的工程应用价值。     

Analytical study of trichlorfon residues in Kaki fruit and cauliflower samples by liquid chromatography-electrospray tandem mass spectrometry

A detailed analytical study on trichlorfon residues in selected vegetables samples has been carried out, focused on the reliable quantification and confirmation of this compound, and on stability of residues under storage. As a consequence, a rapid and sensitive LC-ESI-MS/MS method has been developed for the determination of residues of this insecticide in kaki fruit (flesh and peel) and cauliflower samples. Extraction was performed with acetonitrile using a high-speed blender. After 4-fold dilution of the extract with water, 20 microL was directly injected in the LC-ESI-MS/MS system (triple quadrupole), using matrix-matched standards calibration for quantification. Under optimized MS/MS conditions, limit of detections between 0.006 and 0.013 mg/kg were reached, and a limit of quantification of 0.05 mg/kg was established, with a runtime of only 15 min. Recoveries from spiked blank samples at 0.05 and 0.5 mg/kg were in the range 83-101% with relative standard deviations lower than 10%. The method was applied to treated and untreated samples collected from field residues trials, using quality control samples analysis for the evaluation of the method. Despite the acquisition of two MS/MS transitions in selected reaction monitoring mode, the analysis of treated samples revealed the presence of a chromatographic peak close to the analyte that corresponded to a trichlorfon isobaric compound that shared the same MS/MS transitions. This unusual situation in LC-MS/MS-based procedures required the application of an efficient chromatographic separation to avoid this interference. All experiments have been made in compliance with the principles of Good Laboratory Practices (GLP) and following the European SANCO guidelines for pesticides residue analysis (PRA).     

Changes in the rheological properties and density of a loamy sandy soddy-podzolic soil under the impact of a wheel tractor

Theoretical investigations and field tests have revealed the tendencies of the rheological properties and density of a loamy sandy soddy-podzolic soil under the impact of a wheel tractor. The rheological properties of the soil in the viscoelastic state have been described by a differential equation of the first order relating the compressive stresses with the variation rates of the compressive stresses and the relative vertical compressive deformation. The effect of the dynamic loads at the vertical vibration of a wheel tractor has been mathematically simulated. A method has been proposed for calculating the rheological properties and the soil compaction parameters under a running tractor that considers the effect of the variations of the dynamic load on the soil. Software products have been developed to implement this method. The effect of the main factors on the rheological properties of the soil and its compaction parameters under the impact of a tractor has been quantified.     

水土保持工程的政府投资风险分析

以投资风险评估理论为基础,结合政府水土保持投资风险的特点,研究投资风险辨识体系,在全项目风险结构分解的基础上,提出基于蒙特卡洛风险模拟的政府水土保持投资风险分析方法,并以某水土保持工程为案例进行计算。结果与预期一致,表明用该投资风险分析方法可进行水土保持工程的政府投资风险分析。     

On the determination of total heavy metal content in saline soils and soils rich in organic matter

Abstract

Methods of soil decomposition for determination of heavy metal total content were considered. Two saline soils (chloride and sulphate solonchak solonetz) and one rich in organic matter were uzed for investigation. It has been established that decomposition by using HF‐HCl with a preliminary ignition at 500°C is a very suitable method. The type of the studied soils and the results obtained allow for this method to be recommended for decomposition of various soils.

On the basis of experiments with modelled soils it has been proved that possibilities for heavy metal losses on ignition are created when NaCl content and the percentage of weakly bound heavy metals (water‐soluble, exchangeable, etc.) are high. Under the conditions of the experiment (acid soils ‐ pH 4.3 and 5.0) losses of Zn and Pb but not of Cu have been incurred. Although these cases are not typical, this requires the applicability of the method for such particular occasions to be checked.     

基于多尺度形态学大豆图像滤波方法

提出了一种基于多尺度形态学滤波算法,用于减少噪声影响从而提高大豆图像质量。首先用多尺度结构元素分别对原图像进行开闭重建运算,构造形态学开闭塔;然后计算相邻尺度形态学开闭重建图像间的差,构造亮特征和暗特征的差异塔;最后根据不同尺度的亮特征和暗特征重建图像。通过一组被不同噪声污染的大豆图像验证该文提出的滤波算法,并采用一些标准的评估方法将该文方法与文中提到的其它滤波方法在不同噪声污染情况下进行比较,试验结果表明本文方法的滤波效果优于其它方法。     

Rapid Mercury Analysis for the Field: Method Development and Application to Natural Gas Utility Sites

A new technique based on traditional concepts has beendeveloped for rapid, on-site analysis of mercury inenvironmental media. In this method, mercury isanalyzed by integration of thermal decomposition,amalgamation, and atomic absorption spectrometry(TDA-AAS). Sample preparation and analysis areessentially integrated into a single instrumentalsystem; solid samples can be analyzed directly,without chemical pre-treatment, in an analysis time ofapproximately 5 minutes per sample. A wide range ofstandard reference material has been analyzed byTDA-AAS. Agreement with the certified values at the95% confidence interval for all matrices testedvalidates this technique. Subsequent to validation,TDA-AAS has been used in a series of field studies inconjunction with remediation of mercury-contaminatedsoil at natural gas utility sites. Reasonableagreement has been demonstrated between TDA-AASon-site results and laboratory results usingconventional mercury analysis techniques. Independentlaboratory confirmation of the field data is notrequired as TDA-AAS demonstrates lab-quality resultson-site. This field technique has been shown tosurpass traditional laboratory methods in terms ofboth precision and detection limits. A method for theUnited States Environmental Protection Agency (USEPA), Method 7473, has been developed and validatedbased on TDA-AAS methodology (US EPA, 1998).     

Rapid determination of total cholesterol in homogenized milk

A rapid method that is amenable to automation has been developed for the determination of total cholesterol in homogenized milk. The milk sample is saponified in ethanolic KOH in the presence of an internal standard, cholestane. Cholesterol and the internal standard are then isolated by solid-phase extraction on a nonpolar adsorbent and eluted with organic solvent. The evaporated extract is derivatized and analyzed by capillary gas chromatography. Average recovery of cholesterol acetate added to milk prior to saponification was 95%. The average relative standard deviation for repeated analyses was 2%. The limit of detection for this method is 2 mg/100 g. Twenty samples can be analyzed by one analyst in a normal work day if the gas chromatograph is equipped with an autosampler. This method has been compared with a modified AOAC method for the determination of total cholesterol. At a confidence level of 95%, no difference was observed between the 2 methods.     

Determination of trace levels of bromate in flour and related foods by ion chromatography

In this paper, a method of determining trace levels of bromate in flour and related foods by ion chromatography with large volume injection has been proposed. The detection of bromate was performed with a suppressed conductivity detector after separation on an IonPac AS19 column with KOH as the gradient eluent. Parameters affecting the extraction efficiency of bromate, such as the flour-to-water ratio, extraction time, and temperature, were studied in detail. The optimized pretreatment process was then selected. By using the large volume injection technique, the solution detection limit was decreased to 0.5 microg/L. The linear range of this method was from 5 to 1000 microg/L, and the linear correlation coefficient was 0.9998. The method has been applied to the detection of bromate in flour and related foods, and different concentration levels of bromate were detected in various samples. The spiked recoveries ranged from 86 to 110%. The relative standard deviation (RSD) of the bromate peak height for the seven successive injections of the flour sample was 6.4%.     

农药喷洒雾滴粒径分布数值分析方法

雾滴谱作为衡量喷头雾化性能的重要指标,可用激光雾滴粒径仪测定,但是此设备成本高、操作复杂,不能方便快速地测得雾滴谱。该文以ULLN模型为基础,用3种雾滴谱DV0.1、DV0.5和DV0.9提供的信息作为已知条件,设计了Newton迭代格式并反算出ULLN模型中相关系数,从而确定了模型的具体表达形式,随后利用辛普森数值积分的方法,计算出各雾滴粒径分段所占体积百分率。理论上,由于雾滴谱分布函数已经确定,所以本算法可以计算得到任何雾滴粒径分段的体积百分率。将该方法计算得到的结果和美国俄亥俄州立大学开发的 Driftsim软件计算结果进行了对比,结果表明该算法具有较高计算精度。     

Purge and trap method for determination of ethylene dibromide in whole grains, milled grain products, intermediate grain-based foods, and animal feeds

An improved method has been developed for the determination of ethylene dibromide (EDB; 1,2-dibromoethane) in whole grains, milled grain products, intermediate grain-based foods, and animal feeds. Samples are mixed with water and sparged with nitrogen for 1 h with stirring in a water bath at 100 degrees C. The EDB collected on the adsorbent Tenax TA is eluted with hexane and determined by gas chromatography (GC) with electron capture detection (ECD) and confirmed with Hall electrolytic conductivity detection (HECD) using a second GC column. The highest levels of EDB were also confirmed by full scan GC/mass spectrometry (GC/MS). A total of 24 whole grains, milled grain products, intermediate grain-based foods, and animal feeds analyzed by using this method contained EDB levels up to 840 ppb (wheat). Recoveries from fortified samples ranged from 90 to 105%. Values from this method were compared with those obtained from the acetone soak method; for all 24 samples, this purge and trap method gave equivalent or superior recoveries and detected levels of EDB. Chromatograms for this purge and trap method were clean, enabling a quantitation level of 0.5 ppb to be achieved.     

Spectrophotometric determination of caffeine in coffee products: collaborative study.

An ultraviolet (UV) spectrophotometric method for determining caffeine in regular and decaffeinated coffee products has been studied collaboratively. Nine laboratories participated in this study which compares the proposed UV method with the official AOAC micro Bailey-Andrew method. Caffeine content was determined on as-is basis on 8 samples of green, roasted, and soluble coffees. The coefficients of variation for the proposed method ranged from 2.02 to 6.98% for the 8 samples studied. The results agreed well with those from the Bailey-Andrew Method. The method was adopted as official first action.     

A method for assessing changes in the abundance of butterflies

A method based on transect count has been developed to assess changes in abundance of butterflies from year to year. The method involves weekly walks around atransect route making counts of butterflies seen within defined limits. The transects are divided into sections related to habitat or management units. Walks are made only when weather conditions satisfy specified minimum requirements. The method has been tested for three years at Monks Wood and for two years at a number of other sites.The basis for annual comparisons is an index of abundance which is produced for each brood of each species, except when separation of broods is not possible. This index is correlated with abundance, although the precise nature of the relationship will vary from species to species. Evidence on this presented for two species.The method makes it possible to monitor the abundance of butterflies at selected sites, using recorders, such as nature reserve wardens, who can fit in one or two hours recording each week when the weather is suitable. Such a scheme, based on the methods described in this paper, began in 1976. In addition to the monitoring of fluctuations of abundance, the method provides considerable information on the phenology and ecology of butterflies. The division of the transects into sections makes some assessment of the effects of habitat change, due to management or other factors, possible.     

Rapid and Sensitive Analytical Method for Simultaneous Determination of Imidacloprid and Thiamethoxam Residues in Soils of Sugarcane Ecosystem by Reversed-Phase HPLC

A rapid, simple, sensitive and cost-effective analytical method has been standardised to determine the residues of imidacloprid and thiamethoxam in soil. This method does not require any cleanup with costly sorbents. The recoveries of imidacloprid and thiamethoxam obtained in this no-cleanup method were on par with the protocol involving primary?Csecondary amine-based cleanup. This method requires less volume of solvent (20?mL of acetonitrile/sample) and is suitable for high throughput analyses involving large number of samples. The limit of quantification of the method was 0.01???g/g. Dissipation kinetics of imidacloprid and thiamethoxam in the soils of sugarcane ecosystem was studied by adopting this rapid method. The half-life of imidacloprid and thiamethoxam was 9.07 and 6.22?days when applied at 70 and 100?g a.i./ha, respectively. The dissipation of both the neonicotinoids followed first-order kinetics with good fit.     

Use of 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole for determining cysteine and cystine in cereal and legume seeds

A new colorimetric method has been developed for the determination of chemically available cysteine and half-cystine in maize and legume seeds. The method is based on the reduction of cystine with aqueous NaBH(4)/urea/EDTA solution and the reaction of cysteine with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) in 0.2 M sodium acetate/HCl buffer (pH 2.0) to form a greenish product showing maximum absorbance at 410 nm. The method is simple, accurate, and highly specific for cysteine, in the presence of other naturally occurring amino acids. The method was applied to the determination of cysteine and of cysteine plus half-cystine in some seed meals. There was a good correlation between the results obtained using this method and those obtained using Ellman's reagent [5, 5-dithiobis(2-nitrobenzoic acid)]. There was also a good correlation between the results obtained using this method and cysteic acid values calculated from amino acid analysis of the samples.     

推广软埝田 加快旱塬地治理

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