Determination of the infinite dilution diffusion and activity coefficients of alkanes in polypropylene by inverse gas chromatography

Infinite dilution diffusion and activity coefficients of n‐hexane, n‐heptane, and n‐decane in polypropylene were measured from 373.15 to 393.15 K by inverse gas chromatography. The influences of small molecule solvent and temperature on the infinite dilution diffusion and activity coefficients were investigated. The results showed that the infinite dilution diffusion coefficient decreased but the infinite dilution activity coefficient increased with an increasing number of CH₂ group in the aliphatic solvents. The temperature increase resulted in the increase in the infinite dilution diffusion coefficient and the decrease in the infinite dilution activity coefficient. The graphs plotted according to the results of the infinite dilution diffusion coefficient versus temperature were in agreement with the Arrhenius equation. Diffusion constant and activation energy were obtained from the Arrhenius equation. Also, the interdependence on the infinite dilute activity coefficient and temperature accorded with Gibbs‐Helmholtz equation. From the temperature dependence of the limiting activity coefficients partial molar excess enthalpy at infinite dilution H^E,∞ was obtained. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1925–1930, 2006     

反相气相色谱法测定小分子溶剂在聚乙烯粒子中的无限稀释扩散系数

基于经典线性非平衡色谱过程的矩分析理论,用反相气相色谱法测定了323.15～358.15 K温度范围内二氯甲烷、三氯甲烷、四氯甲烷3种不同相对分子量的同系物小分子及正己烷在聚乙烯粒子中的无限稀释扩散系数。采用聚合物粒子直接填充的色谱柱,考察了温度、同系物小分子分子量及聚乙烯结晶度对扩散系数的影响。实验结果表明,对同一种小分子溶剂/聚乙烯体系,扩散系数均随温度升高而增大。不同相对分子量的同系物小分子在同一种聚乙烯中扩散系数随分子量增加而减小,聚乙烯结晶度增加也会导致扩散系数减小。采用文献中所报道的Krevelen扩散系数预测模型的计算值与实验测量值较为吻合,表明本文所采用的以聚合物粒子直接填充色谱柱的反相气相色谱扩散分析具有一定的可靠性。     

Solvent activity coefficients at infinite dilution in polystyrene-hydrocarbon systems from inverse gas chromatography

Inverse gas chromatography was used to measure activity coefficients of solvents at infinite dilution over a temperature range from 373.15K to 423.15 K for monodisperse polystyrene-hydrocarbon systems. Polystyrene has average molecular weight 2.89 ×10⁵. Solvents include six aliphatic hydrocarbons such as cyclohexane, methylethylketone,n-hexane, carbon tetrachloride, acetonitrile and acetone and three aromatic ones as benzene, toluene andp-xylene. The measured data of activity coefficients of solvents were predicted by UNIFAC-FV model. We, also, presented a modified UNIFAC-FV model by empirically assigning to it a temperature-dependent C parameter in the free volume contribution of the model. Fitted results demonstrated that the modification of the model fitted the experiments better than the original one.     

Solubility and diffusivity of solvents by packed column inverse gas chromatography

Inverse gas chromatography was used with solid polymer particles in packed columns to measure polymer-solvent solubility and diffusion. A new model for this IGC technique has been developed and used to obtain experimental results for n-pentane, isopentane, 1-hexene, n-hexane, and 1-octene solvents in polymer beads of polyethylene. The conditions were measured for solvents at infinite dilution, and experimental data were obtained for the binary polymer-solvent systems in a temperature range from 70 to 100 °C.     

Determination of the diffusion coefficients of organic solvents in polyepichlorohydrin: A comparative study of inverse gas chromatography and sorption methods

The diffusivity of organic solvents in polyepichlorohydrin was studied with two different experimental setups: inverse gas chromatography (IGC) with packed columns and sorption measurements in gravimetric experiments monitored in a Cahn electrobalance. The aim of this work was to test the possibility of solving an inherent problem in the data reduction of IGC measurements, that is, the necessity of characterizing the morphology of the polymer coated on the support (usually given in the so‐called geometric factor of the column). Temperatures between 35 and 65°C were used in the IGC experiments, whereas the sorption measurements were performed between 30 and 40°C. Glass beads were used as supports in IGC for obtaining data concerning the variation of the plate height with the average gas velocity, with which the use of the Van Deemter equation allowed the determination of the diffusion coefficient if the geometric factor was known. In the sorption experiments, the diffusion coefficients at different penetrant activities were directly measured. For their extrapolation within the same concentration range used for IGC (infinite dilution of the penetrant), the theoretical model of Vrentas and Duda was used. By a combination of sorption and IGC experiments, the geometric factor of an IGC column could be adjusted, and this allowed the determination of the diffusion parameters of any other solvent in the same column. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2216–2223, 2003     

UNIFAC and infinite dilution activity coefficients

This paper deals with the possibility of estimating UNIFAC parameters from infinite dilution activity coefficients. Such activity coefficients can be obtained from gas chromatographic measurements (GLC). In some cases the original UNIFAC equations do not represent very well the variations of the activity coefficients with the concentration in the very dilute regions. It is then not possible to estimate reliable parameters from infinite dilution activity coefficients alone. It is shown that a recent modification of the combinatorial part of the UNIFAC equations allows for the estimation of UNIFAC parameters from infinite dilution activity coefficients for alkane—-ketone, alkane—-alcohol, and other mixtures.     

Characterisation of the surface thermodynamic properties of cement components by inverse gas chromatography at infinite dilution

The surface thermodynamic properties of three main inorganic compounds formed during hydration of Portland cement: calcium hydroxide (Ca(OH)₂), ettringite (3CaO·Al₂O₃·3CaSO₄·32H₂O) and calcium-silicate-hydrates (C-S-H), respectively, and one mineral filler: calcium carbonate (CaCO₃), have been characterised by inverse gas chromatography at infinite dilution (IGC-ID) at 35 °C. The thermodynamic properties have been investigated using a wide range of non-polar (n-alkane series), Lewis acidic (CH₂Cl₂ and CHCl₃), Lewis basic (diethyl ether) and aromatic (benzene) and n-alkene series molecular probes, respectively. The tested samples are fairly high surface energy materials as judged by the high dispersive contribution to the total surface energy (the dispersive components γ_s^d range from 45.6 up to 236.2 mJ m^− 2 at 35 °C) and exhibit amphoteric properties, with a predominant acidic character. In the case of hydrated components (i.e. ettringite and C-S-H), the surface thermodynamic properties have been determined at various temperatures (from 35 up to 120 °C) in order to examine the influence of the water content. The changes of both dispersive and specific components clearly demonstrate that the material surface properties are activated with temperature. The changes in the acid-base properties are correlated with the extent of the overall water loss induced by the thermal treatment as demonstrated by thermogravimetric analysis (TGA). The elemental surface composition of these compounds has been determined by X-ray photoelectron spectroscopy (XPS).     

Measurement of infinite dilution activity coefficients of selected environmentally important volatile organic compounds in polydimethylsiloxane using gas - liquid chromatography

Silicon oil, chemically known as polydimethylsiloxane (PDMS), is a high boiling point solvent highly suitable for volatile organic compounds (VOCs) absorption. To use PDMS as an absorption solvent for a specific waste gas problem, it is important to determine the infinite dilution activity coefficients of the VOCs to be separated with PDMS. This work reports activity coefficients at infinite dilution of 13 VOCs in polydimethysiloxane determined by the dynamic gas liquid chromatographic technique. The measurements were carried out at various temperatures (303.15, 313.15, 323.15., 333.15, 353.15, 373.15, 393.15 and 423.15 K). Four PDMS polymers with average molecular weight ranging from 760 to 13,000 were used as solvents. A control column packed by Perkin Elmer to our specifications was used to validate the coating and packing methods. Flow rate dependence of the elution peaks was also investigated by varying it from 10–50 ml/min. Precision was improved by reproducing the results using columns with different liquid loading, thus also studying the retention mechanism. The results compare well with the data from previous work using simple headspace and UNIFAC predictions and literature values. The successful comparison gives an indication of the GLC as a rapid, simple and accurate method for studying the thermodynamics of the interaction of a volatile solute with a nonvolatile solvent.     

Modeling infinite dilution and Fickian diffusion coefficients of carbon dioxide in water

We propose a new model for calculating infinite dilution diffusion coefficients for carbon dioxide and water mixtures. The model takes into account temperature dependence of the dipole moment of water and polarizability of CO₂, and fits experimental CO₂? H₂O data at low and high pressures with an accuracy of 4.9%. Remarkably, the proposed model also accurately predicts infinite dilution diffusion coefficients for other binary water mixtures where solute polarizability is close to that of CO₂, such as CH₄, C₂H₆, C₃H₈, and H₂S. Moreover, we present—to the best of our knowledge—the first predictions of composition‐based Fickian diffusion coefficients for CO₂? H₂O mixtures over the temperature range 298.15–413.15 K, and pressures up to 50 MPa. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Calculation of infinite dilution activity coefficients by the NRTL and UNIQUAC models

Infinite dilution activity coefficients have been calculated for 42 binary systems using the NRTL and UNIQUAC models. Temperature dependent parameters of the models are used in the calculations. These parameters have been estimated by using excess Gibbs free energy and enthalpy of mixing data simultaneously. The calculated values are compared with experimental infinite dilution activity coefficients obtained by extrapolation of vapor-liquid equilibrium (VLE) data published in the literature. The agreement between the calculated and experimental values is poor for highly nonideal system. The selection of the best model is difficult and may be system dependent.     

四氢呋喃等物质在1，4－丁二醇中γ~∞的测定

用色谱法对四氢呋喃等物质在溶剂１，４－丁二醇（ＢＤ）中的无限稀释活度系数进行了测定，采用同一柱温下固定液的流失量与实验测定的时间成正比的方法来推算固定液的流失，经过验证，此校正方法对本文测定是适用的     

Prediction of the temperature dependence of liquid diffusion coefficients at infinite dilution by a group contribution method

1 INTRODUCTIONSince experimental determination of the mutual liquid diffusion coefficients atinfinite dilution is rather complicated,it is important,therefore,to be able to esti-mate the coefficients under various temperatures from one available coefficient ata certain temperature such as 298K.Empirical equations for this purpose are avail-able in many forms.Typical examples are the Wilke-Chang equation and the Tynequation,given below     

毛细管气相色谱测定芳烃组成

利用气相色谱快速、准确的分析特点，建立以SP-3400气相色谱仪及聚乙二醇毛细管柱快速分析芳烃类样品组成的方法，对同一样品测定的相对标准偏差为2.54％。此方法与叫/NL08-59-89芳烃组成测定方法对不同的样品进行分析对比，结果表明，误差范围符合要求，分析速度快，操作简便，可以用于日常分析工作。     

毛细管气相色谱法测定氟硅唑原药含量

建立了毛细管气相色谱法测定氟硅唑原药中氟硅唑含量的方法。方法的准确度高、精密度好,变异系数为0．25％,回收率为99．6％-100．9％。方法快速、简便、准确。     

Determination of tocopherols and sterols by capillary gas chromatography

A method is described for simultaneously determining tocopherols and sterols in fats and oils by quantitative capillary gas chromatography. Samples containing ca. 100 mg of lipid were saponified in capped tubes with aqueous KOH by heating for 8 min at 80 C; the unsaponifiable fraction was extracted with cyclohexane, freed of solvent, derivatized to form the trimethylsilyl ethers of both tocopherols and sterols, and chromatographed on a 50 m×0.25 mm glass capillary column coated with Dexsil 400. Most of the individual tocopherols and common sterols were well separated, although interfering peaks were seen in some samples, which for better specificity should be subjected to an initial purification. For most samples, however, the simplified sample preparation, without preliminary purification, was adequate when combined with capillary gas chromatography. Recovery, method and gas liquid chromatographic precision, and applications are discussed.     

顶空气相色谱法测定罗氟司特原料药中残留溶剂的含量

采用顶空气相色谱法测定罗氟司特原料药中残留溶剂甲醇、丙酮、乙腈、二氯甲烷、乙酸乙酯、甲苯和N,N-二甲基甲酰胺的含量。在DB-624毛细管色谱柱(30 m×0.32 mm×1.80μm)上,以高纯氮气为载气,检测器为氢火焰离子化检测器,进样口温度为220℃,检测器温度为250℃,以程序升温方式使甲醇、丙酮、乙腈、二氯甲烷、乙酸乙酯、甲苯和N,N-二甲基甲酰胺达到了完全分离。结果表明,7种溶剂在对应于限度的50%～150%浓度范围内具有较好的线性关系(R2≥0.99),重复性RSD为1.8%～3.7%,平均回收率为94.9%～108.0%,检测灵敏度均达到了预定的分析要求,在罗氟司特原料药中仅检测出甲醇和丙酮。该方法简便灵敏、准确可靠,适用于罗氟司特原料药质量控制中的残留溶剂检查。     

反气相色谱法研究前沥青烯的表面性质

采用反气相色谱法表征前沥青烯的表面性质,测定了其表面色散自由能及酸碱常数,并基于极性探针的吸附,得到极性探针在前沥青烯表面的极性吸附自由能DG^sp和极性吸附焓DH^sp。结果显示,温度在60～100℃范围内,前沥青烯的表面色散自由能随着温度的升高而逐渐减小。前沥青烯表面的酸常数K_a为0.91,碱常数K_b为2.98,K_b/K_a=3.27。由此可知,前沥青烯为两性偏碱性材料。     

毛细管气相色谱测定染发剂中苯二胺

建立了毛细管气相色谱法测定染发剂中邻、间、对苯二胺含量的分析方法。样品用乙酸乙酯、超声波提取,离心除去杂质,然后采用毛细管分离,FID检测,保留时间定性,峰面积定量。苯二胺三种异构体在0.01~10 g/L浓度范围内线性关系良好,相关系数为0.999 5~0.999 6;邻苯二胺、对苯二胺、间苯二胺加标回收率分别为88.6%~97.8%,93.3%~105.0%,88.5%~99.1%,相对标准偏差为1.94%~2.05%(n=7),检出限分别为2,2.5,2 ng/mL。该方法简单、快速应用于实际样品测定,结果满意。     

顶空气相色谱法测定有机废水中多种残留溶剂的含量

建立了顶空-气相色谱法对有机废水中石油醚(30-60)、丙酮、四氢呋喃、乙酸乙酯、甲醇、乙醇、乙腈的含量进行测定的方法;并对顶空分析条件和气相色谱分析条件进行了优化。实验结果表明,最佳顶空分析条件为:样品体积为5 mL,平衡温度为80℃,平衡时间为30 min,NaCl加入量为1.0 g。7种残留溶剂在各自浓度范围内与峰面积呈良好的线性关系,相关系数均大于0.999。该方法的检出限为0.052～3.96μg/mL,精密度(RSD)为1.3%～6.1%(n=6),加标回收率为83.4%～111.6%(n=3)。该方法操作简便,重现性好,结果准确,适用于有机废水中残留溶剂含量的测定。     

Analysis of volatile fatty acids in biological specimens by capillary column gas chromatography

A method was developed to analyze and quantify volatile fatty acids (VFA) such as acetic, propionic, butyric, isobutyric, valeric and isovaleric acids in biological specimens. To obtain good sample transfer into the chromatographic system an organic solvent had to be used together with an aqueous milieu, thus improving wetting properties of the liquid sample plug introduced into the column. Sample preparation was carried out under alkaline conditions in order to exclude or minimize sample losses due to sample transfer during the extraction and work-up procedure. A cold on-column injection was applied to avoid irregular discrimination of the various acids due to sample splitting and an automatic injection technique was used to accommodate the large number of samples generated from biological origin. Connection of a pre-column of wide internal diameter (0.53 mm) to the analytical column (0.32 m) was optimized and adapted to the nature of the injection solvent mixture consisting of acetonitrile, water and hydrochloric acid. To obtain well-separated and correctly quantifiable gas chromatographic peaks, it was essential to perform the chromatography under acidic aqueous conditions. Standard resolution conditions and response factors were evaluated. The chromatographic results of applying this method to biological specimens from both rats and humans are provided.