Efficiency of methods for Karl Fischer determination of water in oils based on oven evaporation and azeotropic distillation

The efficiency of azeotropic distillation and oven evaporation techniques for trace determination of water in oils has recently been questioned by the National Institute of Standards and Technology (NIST), on the basis of measurements of the residual water found after the extraction step. The results were obtained by volumetric Karl Fischer (KF) titration in a medium containing a large excess of chloroform (> or = 65%), a proposed prerequisite to ensure complete release of water from the oil matrix. In this work, the extent of this residual water was studied by means of a direct zero-current potentiometric technique using a KF medium containing more than 80% chloroform, which is well above the concentration recommended by NIST. A procedure is described that makes it possible to correct the results for dilution errors as well as for chemical interference effects caused by the oil matrix. The corrected values were found to be in the range of 0.6-1.5 ppm, which should be compared with the 12-34 ppm (uncorrected values) reported by NIST for the same oils. From this, it is concluded that the volumetric KF method used by NIST gives results that are much too high.     

Determination of the analytical performance of a headspace capillary gas chromatographic technique and karl Fischer coulometric titration by system calibration using oil samples containing known amounts of moisture

Over the past few years, concerns have been raised in the literature about the accuracy of the Karl Fischer (KF) method for assessing moisture in transformer mineral oils. To better understand this issue, the performance of a static headspace capillary gas chromatographic (HS-CGC) technique was compared to that of KF coulometric titration by analyzing moisture in samples containing known amounts of water and various samples obtained from the National Institute of Standards and Technology (NIST). Two modes of adding samples into the KF vessel were used: direct injection and indirect injection via an azeotropic distillation of the moisture with toluene. Under the conditions used for direct injection, the oil matrix was totally dissolved in the anolyte, which allowed the moisture to be titrated in a single-phase solution rather than in a suspension. The results have shown that when HS-CGC and combined azeotropic distillation/KF titration are calibrated with moisture-in-oil standards, a linear relation is observed over 0-60 ppm H(2)O with a correlation coefficient better than 0.9994 (95% confidence), with the regression line crossing through zero. A similar relation can also be observed when calibration is achieved by direct KF addition of standards prepared with octanol-1, but in this case an intercept of 4-5 ppm is noted. The amount of moisture determined by curve interpolation in NIST reference materials by the three calibrated systems ranges from 13.0 to 14.8 ppm for RM 8506 and 42.5 to 46.4 ppm for RM 8507, and in any case, the results were as high as those reported in the literature with volumetric KF titration. However, titration of various dehydrated oil and solvent samples showed that direct KF titration is affected by a small bias when samples contain very little moisture. The source of error after correction for the large sample volume used for the determination (8 mL) is about 6 ppm for Voltesso naphthenic oil and 4 ppm for toluene, revealing a matrix effect on the measurement. Finally, the results revealed that HS-CGC is a good technique for measuring moisture in oil samples and that the use of azeotropic vapors for introducing moisture into the titrator almost completely eliminates the matrix effect observed with the oil components. Direct KF injection could also be used provided the system is calibrated with moisture-in-oil standards prepared in the same matrix which is to be used for the determination.     

共沸蒸馏法制备单分散氧化镍微粉

先采用均匀沉淀法制得单分散的氧化镍前驱体粉末 ,然后用正丁醇进行共沸蒸馏脱水处理。经干燥、煅烧后成功地制成了单分散性相当好的氧化镍微粉。实验证明 ,共沸蒸馏能有效地脱除湿粉末中的水分 ,丁氧基取代了颗粒表面的羟基 ,从而防止了颗粒间Ni—O—Ni的形成 ,消除了硬团聚形成的可能性。     

Source of the Difference between the Measurement of Water in Hydrocarbons As Determined by the Volumetric and Coulometric Karl Fischer Methods

The disparity between the volumetric and coulometric Karl Fischer methods for the measurement of water in hydrocarbons and hydrocarbon mixtures (oils) has been resolved. The amount of water detected by the volumetric method when the titration vessel solution is homogeneous is higher than that measured coulometrically or volumetrically when the titration vessel solution is heterogeneous. Water in oil that is not measured by the coulometric method when the oil is incompletely dissolved has been shown to reside in the oil phase of the heterogeneous (multiphasic) coulometric vessel suspension. Water that is not measured volumetrically under relatively low chloroform concentrations after the point of transition to a heterogeneous titration vessel solution is reached also appears to reside in the nonaqueous phase of the titration vessel solution. It appears that this water is retained in the hydrocarbon phase in a manner such that it is completely inaccessible to the volumetric or coulometric Karl Fischer reagents.     

Study on drying stage of nanoscale powder preparation

Nanoscale barium titanate powders of cubic phase were prepared by solprecipitation method following three kinds of drying stages: freeze drying, azeotropic distillation and oven drying. Freeze drying is the most effective procedure, though both freeze drying and azeotropic distillation stages are successful in preventing hard agglomerate formation and improving the sinterability of powder. The mechanism by which the drying stage prevents the formation of hard agglomerates was investigated.     

油页岩灰渣提取纳米α-Al_2O_3的方法研究

以油页岩为原料合成纳米α-Al2O3,采用表面活性剂超声辅助分散制备氢氧化铝前躯体,再用共沸蒸馏干燥的综合处理制备超细纳米氧化铝,并以共沸蒸馏法干燥,用XRD、TEM、BET进行分析,用热重/差热、红外、XPS进行表征,实验结果表明,所得的纳米氧化铝分散均匀,粒径为50-80nm,表面活性剂超声结合共沸蒸馏的方法对防止前躯体硬团聚很有效。     

纳米粉体干燥方法的研究

采用三种干燥方法：冷冻干燥、共沸蒸馏和烘箱干燥对溶胶-沉淀法制备的沉淀进行干燥处理,得到了立方相BaTiO₃纳米粉．研究发现：冷冻干燥和共沸蒸馏都能防止粉体中形成硬团聚,提高了烧结活性,其中冷冻干燥法效果更明显．文章同时对两种干燥方法防止硬团聚形成的机理进行了讨论．     

Measuring techniques for autogenous strain of cement paste

Volumetric measurement of autogenous strain is frequently performed by placing the fresh cement paste in a rubber membrane submerged in water. The volume change of the cement paste is measured by the amount of water displaced by the submerged sample. Volumetric and linear measurements of autogenous strain should in principle give identical results. However, the measuring results from the volumetric method are typically 3–5 times higher than the results from the linear technique. In this paper, water uptake from the buoyancy bath through the rubber membrane is identified as the principal artefact of the volumetric method. Water absorption is driven by a lowering of the water activity in the cement paste due to dissolved salts in the pore fluid and to self-desiccation. From the moment of casting, significant water uptake was registered in all experiments. This water uptake influenced the volumetric measurements by the same order of magnitude as the autogenous strain itself. By performing the measurements in a paraffin oil bath instead of a water bath, this artefact was eliminated. Furthermore, volumetric measurements performed in paraffin oil gave almost identical results as linear measurements performed on the same cement pastes.     

Antibacterial and photocatalytic activity of ZnO nanoparticles from Zn(OH)2 dehydrated by azeotropic distillation,freeze drying,and ethanol washing

In this study, the antibacterial and photocatalytic activities of a series of ZnO nanoparticles (NPs) produced using different dehydration methods on as-prepared zinc hydroxide precipitates (Zn(OH)₂) have been investigated. Oven drying, azeotropic distillation, freeze drying, and ethanol washing methods were compared for their ability to yield non-agglomerated powders after precipitation synthesis. β-Zn(OH)₂ single phase was observed after ethanol washing, oven drying, and freeze drying procedures, while azeotropic distillation transformed β-Zn(OH)₂ into ZnO before calcination. Nanosized powders with high surface areas were produced via sublimation during the freeze drying process, and by replacement of hydroxyl groups on the precipitate surface with butoxy groups during azeotropic distillation. Both the photocatalytic degradation of Rhodamine B and the antibacterial activity against the pathogens Escherichia coli and Staphylococcus aureus were enhanced for dehydration methods that increased the surface area of ZnO NPs, suggesting that both photocatalytic and antibacterial behaviors were governed by similar mechanisms.     

废旧油墨的再生处理与利用的研究

目前废弃的油墨越来越多,对废弃物大多采取焚烧和掩埋的方式进行处理,对环境造成了极大的污染。采用对废旧油墨进行共沸蒸馏的方法,去除废弃油墨中大量的溶剂和水(润版液),经研磨、调色等加工处理,使废弃的油墨变为黑色油墨,进行再利用,并减少废弃物对环境的污染。     

Bias assessment of current technologies used for the determination of low levels of moisture in mineral oil samples

The problem in the current debate on the accuracy of Karl Fischer (KF) titrations lies in the fact that coulometry is being compared to volumetry on mineral oil samples for which the true moisture content is unknown. To clarify this point, dehydrated oil samples equilibrated under known temperature and relative humidity conditions and equilibrated oil samples containing known amounts of added moisture were used to assess the accuracy of the determinations. In addition, the measurements were extended to other techniques given that it is unlikely that they would be affected by the same phenomenon causing the KF systematic errors. The samples sent to different laboratories were analyzed by headspace/capillary gas chromatography, gas-phase H2 sensor, oil-phase or gas-phase RH sensors, KF coulometric titration with direct or indirect injection, and KF volumetric titration using a standard or NIST modified procedure. The laboratory comparison showed that with the exception of 4 techniques out of 10 that were tested, the measurements gave results in the expected concentration range. Considering the exceptions, two techniques based on volumetric titration yielded results tainted with an important positive bias for both sample types. This bias, tentatively associated with the high iodine end point concentration used by these systems, was estimated at approximately 22 ppm under the conditions applied by NIST. On the other hand, the two RH sensors showed a marked tendency to underestimate the value of the samples containing high moisture content. In this case, a loss of analyte through wall adsorption during the time required to achieve steady-state conditions in the measuring chamber seems to be at the origin of the negative biases.     

沉淀-共沸蒸馏法合成超细钴蓝颜料的研究

利用沉淀-共沸蒸馏法合成超细钴蓝颜料,并采用扫描电镜(SEM)、X射线衍射(XRD)、荧光反射仪现代分析测试技术对样品性能进行表征.结果表明,用正丁醇共沸蒸馏能有效防止干燥过程中颗粒间的团聚.经1000℃煅烧2h后的钴蓝粉体材料具有良好的分散性、结晶度高、外形规则.其蓝光波段反射率为67 %,红光波段反射率为13 %,达到彩色显象管用钴蓝颜料的要求.为实现性能优异、超细钴蓝的国产化提供了借鉴意义.     

In Vitro Dissolution Profile of Theophvlline Lorded Ethvl Cellulose Microspheres Preprred by Emulsificrtion Soluent Eurporrtion

Theophylline was entrapped in ethyl cellulose microspheres by a water/oil/water emulsification-solvent evaporation method. Aqueous solution of drug was emulsified into a solution of ethyl cellulose in toluene, containing polyisobutylene as protective colloid, followed by emulsification of this primary emulsion into an external aqueous phase to form a water/oil/water emulsion. Microspheres was formed after solvent evaporation and precipitation of ethyl cellulose. In vitro dissolution profile and effect of polyisobutylene on it were studied.     

Modeling evaporation using models that are not boundary-layer regulated

Experimentation shows that oil is not strictly air boundary-layer regulated. The fact that oil evaporation is not strictly boundary-layer regulated implies that a simplistic evaporation equation suffices to describe the process. The following processes do not require consideration: wind velocity, turbulence level, area, thickness, and scale size. The factors important to evaporation are time and temperature. The equation parameters found experimentally for the evaporation of oils can be related to commonly available distillation data for the oil. Specifically, it has been found that the distillation percentage at 180 degrees C correlates well with the equation parameters. Relationships have been developed enabling calculation of evaporation equations directly from distillation data: percentage evaporated = 0.165 (%D)ln(t) where %D is the percentage (by weight) distilled at 180 degrees C and t is the time in minutes. These equations were combined with the equations generated to account for the temperature variations: percentage evaporated = [0.165(%D)+0.045(T-15))ln(t) The results have application in oil spill prediction and modeling. The simple equations can be applied using readily available data such as sea temperature and time. Old equations required oil vapour pressure, specialized distillation data, spill area, wind speed, and mass transfer coefficients, all of which are difficult to obtain.     

In Vitro Dissolution Profile of Theophvlline Lorded Ethvl Cellulose Microspheres Preprred by Emulsificrtion Soluent Eurporrtion

Abstract

Theophylline was entrapped in ethyl cellulose microspheres by a water/oil/water emulsification-solvent evaporation method. Aqueous solution of drug was emulsified into a solution of ethyl cellulose in toluene, containing polyisobutylene as protective colloid, followed by emulsification of this primary emulsion into an external aqueous phase to form a water/oil/water emulsion. Microspheres was formed after solvent evaporation and precipitation of ethyl cellulose. In vitro dissolution profile and effect of polyisobutylene on it were studied.     

共沸蒸馏法合成CeO2纳米颗粒研究

分别以乙醇、正丙醇、异丙醇、正丁醇、异丁醇、仲丁醇及叔丁醇等七种有机醇作为共沸剂,采用液相沉淀法结合共沸蒸馏处理前驱体成功合成了分散性良好、粒子尺寸分布为10-20nm的纳米CeO2颗粒,运用TG／DTA、FI—IR、XRD、TEM等方法对不同有机醇的共沸蒸馏作用以及产品性能进行了分析和表征,探讨了共沸蒸馏法制备纳米CeO2的机理。结果表明：共沸蒸馏能起到有效脱除前驱体凝胶中的水分,防止其干燥和焙烧过程中的硬团聚形成的作用,其中七种醇中以正丁醇的共沸蒸馏效果最佳,所得纳米CeO2颗粒的粒度、均匀及分散性能最好。     

超声模板法制备纳米二氧化铈的研究

采用超声模板法结合共沸蒸馏和水热法处理前驱体成功制备出了纳米CeO2颗粒,通过TEM、XRD、FT-IR、UV-Vis等分析方法对产物形貌、结构和性能进行了表征;研究了模板剂的性质、模板剂的用量、共沸蒸馏和水热处理对纳米CeO2颗粒形态、尺寸的影响。实验结果表明,与OP-10和SDBS比较,CTAB最适合应用于制备纳米CeO2颗粒。当模板剂用量为n(CTAB)∶n(Ce(NO3)3.6H2O)=1∶2,制备出粒径约为6.1nm的球形纳米CeO2;共沸蒸馏能有效去除前驱体中的模板剂和吸附水,丁氧基的取代吸附及其空间位阻作用有利于制得分散性好、粒度分布均匀、粒径约为1.5～2.2nm的纳米CeO2颗粒;水热处理改善了纳米CeO2颗粒的晶化度,避免了高温焙烧过程时硬团聚体的生成,颗粒尺寸为2.5～3.8nm;纳米CeO2颗粒具有良好的可见光透过和优异的紫外光吸收性能。     

Importance of solubility in the sample preparation of poly(ethylene terephthalate) for MALDI TOFMS

The role of solubility in the sample preparation process for matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is demonstrated for oligomeric and medium molar mass poly(ethylene terephthalate) (PET). For low molar mass oligomers (PET-1), minor discrimination effects were observed when the sample was not completely in solution. MALDI spectra of medium molar mass PET, representative of the entire molar mass distribution, were obtained only when a good solvent for PET was used, such as 1,1,1,3,3,3-hexafluoro-2-propanol (commonly referred to as HFIP), as the sample preparation solvent and dithranol as the matrix. The azeotropic composition of 70:30 CH(2)Cl(2)/HFIP better solubilizes the more nonpolar matrixes, which enables more latitude in selecting sample preparation conditions than pure HFIP. Segregation effects were observed when the azeotrope mixture was diluted with tetrahydrofuran, resulting in large molar mass distribution discrimination effects in the MALDI spectra. Dilution with CH(2)Cl(2) resulted in a significant decrease in the overall signal intensity for the entire polymer distribution. With each attempt to dilute the azeotrope, the sample after solvent evaporation was visibly heterogeneous, which resulted in shot-to-shot variability. Both examples demonstrate the importance of constant solvent composition during solvent evaporation. The compatibility of matrix and polymer was explored using relative HPLC retention times. Consistent with previous work in our laboratories, it was found that the matrix/polymer combination that has the closest match of retention time resulted in the best MALDI signal intensity.     

Effect of water removal on the textural properties of resorcinol/formaldehyde gels by azeotropic distillation

The resorcinol/formaldehyde gels containing 5% (w/v) of reactants have been prepared. After curing for seven days, the gel is treated with trifluoroacetic acid to initiate the condensation of hydroxymethyl groups. Drying of the prepared gels is done by removing water with the help of vacuum heterogeneous azeotropic distillation using amyl acetate and n-butanol. The textural properties of the gels thus obtained are compared with the properties of the gel obtained from exchange of water by acetone (control experiment). The pore volume and average pore diameter of the gel obtained from the azeotropic distillation of water with amyl acetate are 0.7663 × 10–3 m3/kg and 0.0145 m, respectively. These values are 1.5 times higher than the values obtained by vacuum heterogeneous azeotropic distillation with n-butanol and about twice than the values obtained in the control experiment. The surface areas in all the three gels are almost constant.     

无团聚纳米氧化锆的制备及应用

采用高分子表面修饰－共沸蒸馏工艺成功地制备了纳米氧化锆微粒;合成过程中高 分子的空间位阻作用阻碍了前驱体颗粒的长大,通过与正丁醇的共沸蒸馏有效地脱除了前驱体 内的水分,在颗粒表面形成了正丁醇分子的包裹结构,在随后的干燥过程中避免了颗粒间形成 强化学键,获得了平均粒径在２０ｎｍ的无团聚的纳米微粒．纳米氧化锆微粒加入到润滑脂中能 明显改善后者的耐磨性能．