共查询到20条相似文献,搜索用时 31 毫秒
1.
Sulfur is determined in sebacate-base lubricants spectrophotometrically and gravimetrically. In the spectrophotometric method, a 0.2–0.3-g sample is treated with mixed acids, magnesium chloride is added, and the solution is evaporated to dryness. The sulfate is reduced to hydrogen sulfide by treatment with a mixture of hydriodic. hypophosphorous, and hydrochloric acids, and the hydrogen sulfide is distilled into ammonia solution. Lead citrate reagent is added and the brownish yellow color of lead sulfide sol is measured. An improved technique and apparatus for the distillation is described. In the gravimetric method, a 5-g sample is treated with mixed acids, antimony and tin are volatilized by treatment with hydrobromic acid, and sulfur is precipitated as barium sulfate. The recommended range of the spectrophotometric method is 0.005–0.15%,and that of the gravimetric method is 0.01–1% sulfur. 相似文献
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为实现对卡塞格林光学系统中的非球面主镜表面面形的高精度检测,设计了一种二元位相型计算全息图(CGH)。介绍了工作原理,对CGH的相位模型参数的优化设计、衍射次级分离以及台阶位置与深度计算等关键问题进行了讨论。通过引入虚拟玻璃的概念快速建立非球面检测模型,针对卡塞格林系统主镜中心开孔的特点,通过加入同轴载波实现了衍射次级的完全分离,相比目前常用的倾斜载波方法简化了相位量化复杂度,数值仿真计算出了最优的台阶深度,降低了加工难度。给出了相应的设计方法及实例,研制投产了CGH。测试得到主镜面形的均方根误差为0.018λ,并与传统补偿器结果(RMS=0.019λ)进行对比,两者测试结果吻合,验证了该设计与检测方法的正确性,该设计方法简单快捷,适用于卡塞格林光学系统主镜面形检测。 相似文献
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Chloramine-T is a disinfectant being developed as a treatment for bacterial gill disease in cultured fish. As part of the drug approval process, a method is required for the confirmation of chloramine-T residues in edible fish tissue. The marker residue that will be used to determine the depletion of chloramine-T residues from the edible tissue of treated fish is para-toluenesulfonamide (p-TSA), a metabolite of chloramine-T. The development and validation of a procedure for the confirmation of p-TSA is described. Homogenized fish tissue is dried by mixing with anhydrous sodium sulfate, and the mixture is extracted with methylene chloride. The extract is passed through a silica gel solid-phase extraction column, from which p-TSA is subsequently eluted with acetonitrile. The acetonitrile extract is evaporated, and the oily residue is dissolved in hexane. The hexane solution is shaken with fresh acetonitrile. The acetonitrile solution is evaporated and the residue is redissolved in dilute potassium hydroxide solution. The aqueous solution is extracted with methylene chloride to further remove more of the fat co-extractive. The aqueous solution is reacted with pentafluorobenzyl bromide in presence of tetrabutylammonium hydrogensulfate. The resulting di-(pentafluorobenzyl) derivative of p-TSA is analyzed by gas chromatography/mass spectrometry. This method permits the confirmation of p-TSA in edible fish tissue at 20 ppb. 相似文献
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采用多段升温法将壳聚糖改性,合成了取代度为1.84、平均分子量为3.08×105、等电点为7.28的N,O-羧甲基壳聚糖(CMC),分别用紫外光谱、红外光谱、荧光光谱对其结构进行了表征,并对其水溶液的Zeta电位、电导率、表面张力以及水分散体系中羧甲基壳聚糖微粒的粒径分布进行了研究.结果表明, N,O-羧甲基壳聚糖具有表面活性;介质的pH值和浓度对羧甲基壳聚糖溶液的稳定性有很大的影响. 相似文献
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氟吗啉是一种新型杀菌剂, 合成工艺热危险性和动力学研究将解决工程问题, 并保障安全生产. 采用差示扫描量热-热重分析仪(DSC-TG)测试主要原料、中间体和产品的热稳定性, 采用反应量热仪(RC1)研究反应热行为, 同时开展反应动力学研究. 研究结果显示, 主要中间体(3,4-二甲氧基苯基)(4-氟苯基)甲酮吸热分解温度为559.3 K, 乙酰吗啉吸热分解温度为478.2 K, 氟吗啉吸热分解温度为638.6 K. 氟吗啉合成反应摩尔放热量为15.44 kJ/mol, 绝热温升ΔTad为9.1 K, 本研究合成工艺的热危险性较小. 氟吗啉合成反应动力学方程为:rA=kcAa=8.34×10-3CA0.57, 对主要中间体(3,4-二甲氧基苯基)(4-氟苯基)甲酮的反应级数为0.57 级. 相似文献
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A method for determining traces of sulfate in reagent-grade chemicals is presented. The sample is passed through an alumina column in acid solution to isolate the sulfate, which is then eluted with ammonia. Potassium bromide is added to an aliquot of the eluate, and the solution is freeze-dried. The resulting powder is pressed into a disk whose infrared spectrum is recorded. The method is reasonably accurate and requires a minimum of operator time per sample because a large number of samples can be processed together 相似文献
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水性聚氨酯的制备及其性能的研究 总被引:15,自引:0,他引:15
本文以琥珀酸酐与三羟甲基丙烷反应,制得了含有羟基和羧基的酯类亲水性单体,并以此单体与TDI和PPG-1000反应,制得了含有羧基的聚氨酯预聚体,在三乙醇胺水溶液中分散得到了水性聚氨酯(简称WPU)。本文对预聚体的溶剂种类和用量,对乳胶粒的大小及形状的影响进行了研究,确认溶剂的用量越大,乳胶的粒径就越小;以丙酮作溶剂,乳胶粒为棒状或橄榄球状,而以丁酮为溶剂,得到的乳胶粒为圆球状。通过改变亲水单体的用 相似文献
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We present a new method of measuring the electrophoretic mobility of a particle in a concentrated suspension. The method is used to measure the electrophoretic mobility of PMMA particles (diameter 10 microm) suspended in a mixture of liquid hydrocarbons. The particle volume fraction of the suspension is varied from 0 up to 0.30 and the resulting variation of the electrophoretic mobility is discussed. The suspending liquid is such that its refractive index is very close to that of the particles. Thus the suspension is almost transparent and it is possible to follow through a microscope the motion of one particle. The suspension is subjected to a low-frequency electric field (0.5 Hz). The cell containing the suspension is mounted on a piezoelectric crystal. The displacement that compensates for the particle motion (when the particle image is steady) is determined. 相似文献
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Determination of free, total, and esterified cholesterol by high-performance liquid chromatography 总被引:1,自引:0,他引:1
A method is described for measuring free, total, and esterified cholesterol in blood serum in which reversed-phase liquid chromatography is used and the eluate is monitored at 200 nm. The sample for total cholesterol is prepared according to the Abell-Kendall procedure, and for free cholesterol an extract of serum--isopropanol (1:5, v/v) is used. The column is a muBondapak C18, 10 micrometers, and the mobile phase for total cholesterol is isopropanol--acetonitrile (50:50, v/v); for free cholesterol, it is isopropanol--acetonitrile--water (60:30:10). An approximation of the free cholesterol, triglycerides, and individual cholesteryl esters is obtained from single chromatograms of isopropanol extracts of serum if the first mobile phase is used. In a comparison study with the Abell-Kendall method for total cholesterol, the correlation is excellent and the precision is acceptable. 相似文献
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D241树脂分离纯化黄芩总黄酮的研究 总被引:10,自引:1,他引:10
本文研究了用241树脂分离纯化黄芩总黄酮的方法和工艺。实验结果表明:D241树脂对黄芩总黄酮的静态交换容量是77mg/ml树脂。在pH11.0、流速2.0BV/h、提取液中总黄酮浓度17.5mg/ml条件下,D241树脂对黄芩总黄酮的动态交换容量为43.8mg/ml。用60%甲醇作为黄芩总黄酮洗脱剂,在PH4.0、洗脱流速1.5BV/h条件下,4.5BV洗脱剂即可完全洗脱被D241树脂交换的黄芩总黄酮。与酸沉淀法相比较,经过除去果胶,总黄酮纯度由33.34%提高到74.9%,粗品收得率由11.52%降低至4.83%;经过D241树脂分离纯化,其纯度达到91.5%,产品收得率3.54%。 相似文献
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Wei-Wei Yang You-Ying Di Jing Li Yu-Xia Kong 《The Journal of chemical thermodynamics》2009,41(8):945-950
The crystal structures of ephedrine hydrochloride and N-methylephedrine hydrochloride have been determined by X-ray crystallography. The molar enthalpies of dissolution of the two compounds with various molalities were measured at T = 298.15 K in distilled water by means of isoperibol solution-reaction calorimeter, respectively. According to the theory of Pitzer, the molar enthalpies of dissolution of the two compounds at infinite dilution, , and Pitzer’s parameters , were obtained. Then the values of apparent relative molar enthalpies , hydration heat, and relative partial molar enthalpies of the two compounds were derived from the experimental results of the enthalpies of dissolution of the two compounds. Finally, the ionic radius of the cations can be calculated from the data of the corresponding effective volume of the cations. 相似文献
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Triacylglycerols can be synthesized from glycerol and fatty acids. During this equilibrium reaction water is produced, therefore a mixture of mono-, di- and triesters is obtained. One way to produce an excess of triacylglycerols is to remove the water produced during synthesis. This can be realized in an immobilized enzyme pervaporation system. The enzyme is immobilized onto the lumen side of a cellulose membrane where the organic phase is present. Air circulates at the shell side and the water activity is controlled with the use of a condenser. The lipase catalyzed esterification of decanoic acid and partial glycerides is studied in this reactor. The system is reaction limited. Only at low water activity conditions, an excess of triacylglycerols is obtained. The enzyme activity at the start of the experiments is independent of the water activity within the range studied. Stability is influenced: After 600 hours the activity is 26% of the activity at the start at aw = 0.1 and 71% at aw = 0.45. 相似文献
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Vibrational-translational energy transfer probabilities and collisional efficiencies are calculated for atom-polyatomic molecule collisions. It is assumed that a collision complex is formed and that the total internal vibrational energy is statistically distributed among all the modes of the complex. An attractive potential is assumed and account is taken of the centrifugal barrier. Conservation of system angular momentum is imposed. Convolution of the several thermal distribution functions is carried out and completeness and detailed balance are observed. Comparison of calculated quantum statistical quantities with experiment is made for the thermal isomerization of methyl and ethyl isocyanide in the presence of heavy atomic bath gases, such as Xe or Ar, and semiquantitative agreement is found. 相似文献
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《Sensors and Actuators》1988,13(3):251-262
We present a new type of chemical transducer, the coulometric sensor. This sensor is in fact an integrated sensor-actuator system that is able to measure the concentration of acids and bases by means of coulometric titration. An ISFET is used as the sensor to monitor the pH changes induced by the actuator, which is a gold electrode that fits closely around the ISFET's gate area. Coulometry is an absolute method and therefore the output of the new sensor is only determined by its dimensions and is not subject to changes in offset and sensitivity of the indicator electrode. It is thus expected that the operation of the sensor will be stable for a long time, so that only a one-time calibration is needed. As a first example of this new class of chemical transducers, a carbon dioxide sensor is presented. It is shown that the stability is some orders of magnitude better than that for a ‘classical” potentiometric sensor. 相似文献
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小大之辩是《庄子·逍遥游》的重要论题,对此已形成两种基本解释取向:“小大齐一”和“小不如大”。现代研究者视之为矛盾冲突的表现,解决之道往往是在两者之中选择其一。但这种解决方式犯了误置具体性的错误,合理的解决方式是贞定两种取向的各自有效界域。通过对《逍遥游》的整体研究,可以看到:小不及大的合理界域指向的是心,即生存论的视域与格局,小不及大意味着最大化地扩展生存论视域;小大齐一是就性而言的,每一物之性在质上虽然各不相同,可谓千差万别,根本无法齐等,但皆可通达在己之天,由性而天的道路对每一个存在者都是齐等的,因而,与小大齐一相关联的是,走向适性、足性之路,才能成就主体的自由。主体的自由行程以大其心始,以等齐其性终,在小大之辩的尽头,万物各从其性,不同存在者自性齐等,这就是“天地之正”的世界图景,后者乃是小大之辩的最终归宿。 相似文献
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Susana de Marcos Rubén Hortigüela Javier Gatbán Juan R. Castillo Otto S. Wolfbeis 《Mikrochimica acta》1999,130(4):267-272
A new optical sensor for urea determination is presented. It is based on the enzymatic reaction with urease, which is first photoimmobilized with polyacrylamide onto a chemically polymerized polypyrrole (PPy) film. The main advantage of this sensor is that no indicator dye or pH indicator is needed, because PPy itself acts as the support and the indicator. These PPy films show an absorbance spectrum in the near IR range which is pH dependent. The variation of absorbance is thus directly related to the change of pH caused during the enzymatic reaction, which is also dependent on the urea concentration. The linear range of the sensor is from 0.06 to 1 M of urea, which is the common level of urea concentration found in blood and urine samples. 相似文献