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41.
低温吹扫捕集-气相色谱-火焰光度法测定南极水样中的甲基锡形态 总被引:2,自引:0,他引:2
:建立了低温吹扫捕集 -气相色谱 -火焰光度法快速测定甲基锡形态的新方法。在 p H 5的 HAc- Na Ac缓冲溶液中 ,加入 1 m L浓度为 30 g/L的硼氢化钾 ,一甲基锡 ,二甲基锡和三甲基锡分别转化成相应的氢化物 ,直接被低温吹扫捕集到冷阱毛细管中 ,经过气相色谱分离 ,用火焰光度检测器检测。方法的最低检出限分别为一甲基锡 1 8ng·L-1,二甲基锡 1 2 ng· L-1,三甲基锡 3ng·L-1,相对标准偏差小于 3%。方法已用于测定南极水样中的甲基锡形态。 相似文献
42.
微粉化技术提高水不溶性药物溶解度 总被引:4,自引:0,他引:4
药物的微粉化可以改善颗粒的润湿性,进而提高水不溶性药物的溶解度和溶解速率。目前普遍采用的药物微粒化技术主要包括机械研磨、超临界流体过程、低温喷淋和溶剂蒸发沉积过程。本文介绍了这些微粉化制备技术的基本原理以及该类技术的应用进展。 相似文献
43.
This paper deals with improvements in the measurements of optical power by using CCD-based stabilization optics. Absolute optical power scale has been realized at discrete laser wavelengths of vertically polarized tuneable Ar+, fixed He–Ne and fixed Nd:YAG (with second harmonic) laser sources. Electrical-substitution cryogenic radiometer was operated at the helium temperature for this purpose. To make measurements on the metrological level the intensities of lasers were stabilized to better than 0.004% by using an established system. Using the highly collimated and stabilized lasers, whose beam shape and dimension were adjusted properly, leads us to measure the absolute optical powers with an uncertainty in the order of 10−4. 相似文献
44.
John M. Gary 《国际流体数值方法杂志》1988,8(1):81-90
A numerical method to obtain the neutral curve for the onset of acoustic oscillations in a helium-filled tube is described. Such oscillations can cause a serious heat loss in the plumbing associated with liquid helium dewars. The problem is modelled by a second-order, ordinary differential eigenvalue problem for the pressure perturbation. The numerical method to find the eigenvalues and track the resulting points along the neutral curve is tailored to this problem. The results show that a tube with a uniform temperature gradient along it is much more stable than one where the temperature suddenly jumps from the cold to the hot value in the middle of the tube. 相似文献
45.
Joseph M. Levy Lori Dolata Robert M. Ravey Eugene Storozynsky Kathy A. Holowczak 《Journal of separation science》1993,16(6):368-371
For many applications using supercritical fluid extraction (SFE), modifiers may be required.This paper will present some findings regarding the use of various modifiers including methanol, hexane, acetone, chloroform, dichloromethane, toluene, and tributylphosphate, in on-line and off-line SFE with cryogenic adsorbent trapping. The specific applications involved the extractions of petroleum hydrocarbons and pesticides from naturally incurred soils. 相似文献
46.
The two-dimensional (2D) data structure generated under a high resolution GC×GC system with a small number of samplings taken across the first dimension is evaluated for the purpose of the application of chemometric deconvolution methods. Chemometric techniques such as generalized rank annihilation method (GRAM) place high demands on the reproducibility of chromatographic experiments. For GRAM to be employed for GC×GC data interpretation, it is critical that the separation method provides data with a bilinear structure; the peak-shape and retention times on both columns must be reproducible. With a limited number of samplings across a 1D (first dimension) peak (e.g. four to six samplings) repeatability of the pattern of the modulated peaks (controlled by the modulation phase) becomes important in producing a bilinear data structure. Reproducibility of modulation phase can be affected by both reliability of the modulation period and reproducibility of the retention time of the peak on the first column (which arises from oven temperature and carrier flow rate stability). Evaluation of within-run and run-to-run retention time reproducibility (retention time uncertainty) on both columns, and modulation phase reproducibility using a modulated cryogenic system for a pair of overlapping components (fatty acid methyl esters) was undertaken. An investigation of the quality of data to permit quantification of each component by using GRAM deconvolution, was also conducted. Less than 4% run-to-run retention time uncertainty was obtained on column 1 and less than 9% run-to-run and within-run retention time uncertainty was obtained on column 2, where these R.S.D. measures are reported normalised to peak widths on each respective dimension. The R.S.D. of duplicate quantification results by GRAM ranged from 2 to 26% although the average quantification error using GRAM was less than 5%. 相似文献
47.
Paul V. Doskey 《Journal of separation science》1991,14(11):724-728
A comparison has been made between two cryogenic preconcentration - high resolution gas chromatography techniques for the analysis of non-methane hydrocarbons in ambient air, one involving treatment of air samples with magnesium perchlorate to remove water, the other involving analysis without treatment. Recoveries of C1-, C2-, and C3-substituted benzenes in treated samples were 80%, 50%, and 50%, respectively. Incomplete recovery of C7-C9 n-1-olefins was also observed. C2-C8 hydrocarbons and C2-C6 n-1-olefins were recovered with greater than 90% efficiency. Analyses of certified audit samples containing a mixture of C2-C8 aliphatic and aromatic hydrocarbons at the 20 ppbv level in humidified zero-grade air indicated that the accuracy of the technique for untreated air samples was approximately 90%. The use of magnesium perchlorate for water removal cannot be recommended for the analysis of non-methane hydrocarbons in ambient air. 相似文献
48.
V.I.T.A. de Rooij-Lohmann A.E. YakshinE. Zoethout J. VerhoevenF. Bijkerk 《Applied Surface Science》2011,257(14):6251-6255
Thin interlayers are essential for high-quality multilayer optics. We present the first investigation of reducing the interlayer thickness of Mo/Si multilayer structures by cooling the substrate with liquid nitrogen during the deposition. The structures were deposited by means of electron beam evaporation. Even after warming up to room temperature prior to analysis, the interlayers that formed upon cryogenic deposition were found to be approximately 60% thinner compared to room temperature deposition. The interlayer thickness reduction at low temperature and its preservation upon warming up are attributed to a lower mobility of adatoms, reduced surface segregation of Si during Mo-on-Si growth, and/or crystallization of Mo. 相似文献
49.
《Arabian Journal of Chemistry》2022,15(6):103866
The primary objective of this study is to develop an empirical correlation model that is able to predict the solid–liquid-vapour phase equilibria (SLVE) for the ternary system of N2-Kr-Xe at pressures ranging from 1 to 45 bar and temperatures ranging from 80 to 180 K. The model was based on Peng-Robinson equation of state. To optimize the interaction parameters that are needed in the model, it was first used to correlate the experimental SLVE data found in the literature for the N2-Kr, and N2-Xe and Kr-Xe binary systems. When the corresponding interaction parameters were optimized, the model was then expanded to predict the SLVE and construct the phase envelope of the ternary system of N2 -Kr-Xe. 相似文献
50.