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81.
A method for the direct determination of volatile and non-volatile nickel and vanadium compounds in crude oil without previous treatment using direct solid sampling graphite furnace atomic absorption spectrometry is proposed. The crude oil samples were weighed directly onto solid sampling platforms using a microbalance and introduced into a transversely heated solid sampling graphite tube. In previous work of our group losses of volatile nickel and vanadium compounds have been detected, whereas other nickel and vanadium compounds were thermally stable up to 1300 and 1600 °C, respectively. In order to avoid this problem different chemical modifiers (conventional and permanent) have been investigated. With 400 μg of iridium as permanent modifier, the signal started to drop already after two atomization cycles, possibly because of an interaction of nickel (which is a catalyst poison) with iridium. Twenty micrograms of palladium applied in each determination was found to be optimum for both elements. The palladium was deposited on the platform and submitted to a drying step at 150 °C for 75 s. After that the sample was added onto the platform and submitted to the furnace program. The influence of sample mass on the linearity of the response and on potential measurement errors was also investigated using four samples with different nickel content. For the sample with the lowest nickel concentration the relationship between mass and integrated absorbance was found to be non-linear when a high sample mass was introduced. It was suspected that the modifier had not covered the entire platform surface, which resulted in analyte losses. This problem could be avoided by using 40 μL of 0.5 g L−1 Pd with 0.05% Triton X-100. Calibration curves were established with and without modifier, with aqueous standards, oil-in-water emulsions and the certified reference material NIST SRM 1634c (trace metals in residual fuel oil). The sensitivity for aqueous standards and emulsions was close to that for SRM 1634c, making possible the use of aqueous standards for calibration. The limits of detection and quantification obtained for nickel and vanadium under this condition were found to be 0.02 and 0.06 μg g−1, respectively, for both elements, based on 10 mg of sample. Nickel and vanadium were determined in the samples with (total Ni and V) and without the use of Pd (thermally stable compounds), and the concentration of volatile compounds was calculated by difference. The results were compared with those obtained by high-resolution continuum source graphite furnace atomic absorption spectrometry by emulsion technique; no significant differences were found for total Ni and V at the 95% confidence level according to a Student's t-test. 相似文献
82.
Patricia Cava-Montesinos Agustin Pastor Miguel de la Guardia 《Analytica chimica acta》2003,481(2):291-300
A sensitive procedure has been developed for selenium and tellurium determination in milk by hydride generation atomic fluorescence spectrometry (HG-AFS) after microwave-assisted sample digestion. The method provides sensitivity values of 1591 and 997 fluorescence units ng−1 ml−1 with detection limits of 0.005 and 0.015 ng ml−1 for Se and Te, respectively. The application of the developed methodology to the analysis of cow milk samples of the Spanish market evidenced the presence of concentration ranges from 11.1 to 26.0 ng ml−1 for Se, and from 1.04 to 9.7 ng ml−1 for Te having found a good comparability with data obtained after dry-ashing of samples. 相似文献
83.
84.
通过IR方法,观测并讨论了在不同条件下制备的超高分子量PE(WHMPE)凝胶膜中旁式(G构象)构象与超拉伸性的关系,提出了G构象浓度及分布对UHMPE凝胶膜超拉伸性影响的新概念,同时也讨论了它与链缠结之间的联系,发现:反映G构象的相对浓度的比值σ=I1303I1352随制膜浓度的增大而增加,在临界浓度C0(0.4~0.5g@100ml)附近所形成的膜,具有超高拉伸性(λ=200),其G构象的变化与Matsuo由比浓粘度提出的缠结链改变相对应;热处理温度比热处理时间对σ值的影响更显著,在一定温度下约4分钟后σ值基本不变;在σ值最低的温度范围拉伸,凝胶膜具有良好的超高拉伸性. 相似文献
85.
Minkin V. I. Gribanova T. N. Starikov A. G. Minyaev R. M. 《Russian Chemical Bulletin》2003,52(3):519-525
The electronic and molecular structure of planar (cyclic and linear) tetra- and hexaatomic clusters (XY)
n
(XY = CC, BN, BeO, LiF; n = 2, 3) was studied using the ab initio CCD(full)/6-311+G** method and density functional approach (B3LYP/6-311+G**). The stability of cyclic clusters C6, B3N3, and Be3O3 with D3h
symmetry is mainly determined by the aromaticity of their -electron systems. 相似文献
86.
Based on Thiele-Cohen model, a swelling equation was derived by introducing the interaction parameters of a three-component system of polymer Ⅰ-polymer Ⅱ-solvent, which is a reasonable representation of the swelling behavior of general homogeneous IPNs. The degrees of equilibrium swelling of polyvinyl acetate/polymethyl actylate (PVAc/PMA) IPNs were compared between the theoretical and experimental values. The obvious effects of mutual entanglements were observed. 相似文献
87.
密闭微波消解-冷原子荧光光谱法测定蔬菜中的痕量汞 总被引:1,自引:0,他引:1
采用硝酸和过氧化氢体系,密闭微波消解,冷原子荧光光谱法测定蔬菜中的痕量汞,选择0.3g/L硼氢化钾溶液为还原剂,硝酸溶液(1 99)为酸介质。测定结果表明汞浓度在0~1μg/L范围线性良好,相关系数大于0.9990,汞的加标回收率为90.2%~99.6%,测定结果的相对标准偏差均小于4%,检出限为0.0058μg/L。 相似文献
88.
Fly ash samples of cement works were analysed using slurry nebulization inductively coupled plasma atomic emission spectrometric (ICP-AES). Because of the influence of the experimental factors on the signal intensity, the optimal conditions of the analysis circumstances were determined. Control analyses (wet digestion followed by ICP-AES, and XRF of dry powders (pressed pellets)) were also carried out to compare the results. Based on the result, it was concluded that the slurry nebulization method using slurry standard of same type reference material for calibration can be applied for rapid but less precise (RSD 5–10%) determination of the elements in fly ash. 相似文献
89.
90.
胺、醇、醚类化合物电离能的自相关拓扑研究 总被引:1,自引:3,他引:1
原子的染色序数 fi 定义为 :fi=gi·xi,式中 gi 为原子i在分子中的序数 ,xi 为其染色系数 .基于fi 建立改进的原子序数自相关拓扑指数mF ,其中的1F对烷烃及其衍生物具有良好的结构选择性 .使用第一电离能 (Ip)与0 F ,1F的数量关系模型对 32种脂肪族胺、醇、醚进行估算、预测 ,结果令人满意 相似文献