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71.
土壤及蔬菜中微量汞的同位素稀释电感耦合等离子体质谱测定 总被引:1,自引:0,他引:1
建立了微波消解电感耦合等离子体质谱同位素稀释(ID/ICP-MS)测定微量汞的方法。考察了仪器参数及测量条件对汞同位素比值RHg(202Hg/200Hg)测量的影响,根据同位素比值测量误差的传递因子优化了富集同位素稀释剂(202Hg98%)的加入量,并以铊同位素比值(205Tl/203Tl)作为RHg(202Hg/200Hg)测量时发生质量歧视效应的校正因子;通过反同位素稀释法标定了富集汞同位素稀释剂的浓度。利用所建立的ID/ICP-MS方法测定了杨树叶(GBW07604)和湖积物(GBW07423)2种标准参考物中汞的含量,回收率分别为112%和100%。该方法具有准确度高、精密度好等优点,且样品前处理简便,适用于土壤及蔬菜等样品中微量及痕量汞的准确测定。 相似文献
72.
73.
Olga A. Simakova Pavel A. Simonov Anatoly V. Romanenko Irina L. Simakova 《Reaction Kinetics and Catalysis Letters》2008,95(1):3-12
Pd/Sibunit catalysts were prepared by deposition of palladium hydroxide onto the support surface in an alkaline medium. It
was found that the palladium distribution throughout the catalyst grain, and the dispersion of Pd particles depend on (i) the order of the addition of H2PdCl4 and Na2CO3 to carbon suspension, (ii) Na2CO3 to H2PdCl4 ratio, and (iii) aging time of the mixture H2PdCl4 + Na2CO3 before its addition to the carbon. The catalysts were tested in the hydrogenation of cyclohexene and rapeseed oil under static
conditions. The yield of trans-isomers as products of partial hydrogenation of rapeseed oil was found to decrease with decreasing the Pd particle size in
the catalysts, as well as with increasing the Pd concentration on the periphery of the support grains. 相似文献
74.
75.
固相萃取-高效液相色谱联用分析蔬菜中5种有机磷 总被引:3,自引:1,他引:2
建立了固相萃取(SPE)-高效液相色谱(HPLC)联用测定蔬菜中甲基对硫磷、三唑磷、乙基对硫磷、倍硫磷和辛硫磷的分析方法.采用自制Florisil SPE柱,优化了萃取溶剂、SPE柱填料类型、SPE柱填料用量和SPE淋洗溶剂等前处理条件以及HPLC仪器条件.方法线性范围为0.02~2.00μg/L;检出限介于0.10~0.17μg/g.分析加标实际样品,回收率为76.5%~109.0%,RSD为2.1%~8.0%.方法完全符合蔬菜中痕量有机磷农药残留的快速分析要求. 相似文献
76.
原子吸收法测定蔬菜罐头中铜含量的测量不确定度评定 总被引:7,自引:0,他引:7
对GB/T 5009.13-1996《食品中铜的测定方法》中火争原子吸收法测定蔬菜罐头中铜含量的测量不确定度进行评定,根据JJF1059-1999《测量不确定度评定与表示》技术规范的要求,分析了该测量过程的测量不确定度来源,建立了数学模型,并利用标准样品对测量不确定度的各个分量进行计算,计算得该测定水平下铜含量测定结果的扩展不确定度为0.2mg/kg. 相似文献
77.
Melamine (2,4,6-triamino-1,3,5-triazine) is a nitrogen-rich chemical implicated in the pet and human food recalls and in the global food safety scares involving milk products. Due to the serious health concerns associated with melamine consumption and the extensive scope of affected products, rapid and sensitive methods to detect melamine's presence are essential. We propose the use of spectroscopy data-produced by near-infrared (near-IR/NIR) and mid-infrared (mid-IR/MIR) spectroscopies, in particular—for melamine detection in complex dairy matrixes. None of the up-to-date reported IR-based methods for melamine detection has unambiguously shown its wide applicability to different dairy products as well as limit of detection (LOD) below 1 ppm on independent sample set. It was found that infrared spectroscopy is an effective tool to detect melamine in dairy products, such as infant formula, milk powder, or liquid milk. ALOD below 1 ppm (0.76 ± 0.11 ppm) can be reached if a correct spectrum preprocessing (pretreatment) technique and a correct multivariate (MDA) algorithm—partial least squares regression (PLS), polynomial PLS (Poly-PLS), artificial neural network (ANN), support vector regression (SVR), or least squares support vector machine (LS-SVM)—are used for spectrum analysis. The relationship between MIR/NIR spectrum of milk products and melamine content is nonlinear. Thus, nonlinear regression methods are needed to correctly predict the triazine-derivative content of milk products. It can be concluded that mid- and near-infrared spectroscopy can be regarded as a quick, sensitive, robust, and low-cost method for liquid milk, infant formula, and milk powder analysis. 相似文献
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79.
An interlaboratory comparison by 13C-isotope ratio mass spectrometry was organised by working group No. 1 of the European Commission of Standardisation (CEN/TC 174) in order to define the repeatability (r) and the reproducibility (R) of the 13C determination in sugars and pulp, isolated from the same fruit juice. Six unlabelled juices were analysed in 19 laboratories in the European Union, Australia and the USA. Three samples were authentic juices (orange, grapefruit, pineapple) and the remaining samples were the same juices with an addition of sugar at 15 g l−1 (orange, pineapple) or 11.8 g l−1 (grapefruit). The sugar was prepared by mixing equal amounts of beet and cane sucroses. The different laboratories used the same experimental protocol under different conditions (operator, conversion system for CO2 preparation, mass spectrometer). The results for the sugars (r = 0.27%., R = 0.82%.) were comparable to those from an earlier ring test (r = 0.30%., R = 0.70%.), while the results for the pulp presented higher interlaboratory variability (r = 0.38%., R = 1.89%.) possibly due to experimental difficulties. Nevertheless, the RSDR for free sugars ranged 0.9–3.2% and for pulp, 0.9–9.3%. On the basis of the Horwitz equation and taking account of the concentration of the isotopes measured, an RSDR of 7–8% might have been expected. The experimentally determined RSDR values were less than twice the theoretically expected values, which is a criterion of an acceptable method. The results were therefore considered to be acceptable by specialists in the field of isotopic analysis, and the method applied was found to improve the sensitivity of the 13C determination for the detection of sugar addition in fruit juices. 相似文献
80.
Débora de Oliveira Marco Di Luccio Carina Faccio Clarissa Dalla Rosa João Paulo Bender Nádia Lipke Silvana Menoncin Cristiana Amroginski José Vladimir de Oliveira 《Applied biochemistry and biotechnology》2004,115(1-3):771-780
We studied the production of fatty acid ethyl esters from castor oil using n-hexane as solvent and two commercial lipases, Novozym 435 and Lipozyme IM, as catalysts. For this purpose, a Taguchi experimental
design was adopted considering the following variables: temperature (35–65°C), water (0–10 wt/wt%), and enzyme (5–20 wt/wt%)
concentrations and oil-to-ethanol molar ratio (1∶3 to 1∶10). An empirical model was then built so as to assess the main and
cross-variable effects on the reaction conversion and also to maximize biodiesel production for each enzyme. For the system
containing Novozym 435 as tatalyst the maximum conversion obtained was 81.4% at 65°C, enzyme concentration of 20 wt/wt%, water
concentration of 0 wt/wt%, and oil-to-ethanol molar ratio of 1∶10. When the catalyst was Lipozyme IM, a conversion as high
as 98% was obtained at 65°C, enzyme concentration of 20 wt/wt%, water concentration of 0 wt/wt%, and oil-to-ethanol molar
ratio of 1∶3. 相似文献