摘要:

Supercritical fluid chromatography usingn-pentane as a mobile phase and Porasil C as a column packing was applied to the characterization of Dow-Corning 710 fluid, a commonly used gas chromatographic stationary phase. Under the experimental conditions, decomposition of the polymer was observed on columns of alumina, and derivatized Porasil packings were found to be unstable. Linear pressure programming variables were studied at 206 and 216°C by normalizing the total analysis time on a fixed length of column. A series of homologous polymer components was used to demonstrate the effects upon resolution of density-isotherm nonlinearity associated with the mobile phase. The results showed that optimal temperature conditions existed for the use of linear pressure programming, with the choice of temperature conditions dependent upon the molecular weight range. Operational guidelines are suggested. Mixed solvent behavior was investigated for this separation. The effect of changing the polarity of the mobile phase by adding 0 to 20% v/v isopropanol ton-pentane was studied under isothermal and isobaric conditions. The alcohol was shown to change adsorption characteristics and alter critical constants. The effect upon the critical constants appeared to conform to Kay's approximation. The results suggest that mixed solvents can be used to speed up separations for mixtures having components of widely different adsorption energies. The pseudocritical concept using Kay's approximation was tested for its qualitative ability to estimate state effects when solvents are mixed. The effect of temperature upon migration behavior was compared for equimolar amounts of isopropanol and methanol, each in n-pentane. Kay's approximation appeared to be useful for qualitative predictions regarding changes in critical pressure. However, an attempt to predict density isotherm behavior for 20 % isopropanol in n-pentane relative to pure n-pentane suggested that Kay's approximation may not be as useful for predicting criticla temperature effects.

ISSN:0037-2366    

DOI:10.1080/00372367508058039

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The chemical exchange reaction between amine carbamate and CO2has been investigated for the purpose of using it as a practical method to concentrate13C. The effects of solvent, concentration of amines, catalysts, flow rate, and diameter of the column have been studied for a number of amines. Of the solutions studied, di-n-butylamine (DNBA) in triethylamine (TEA) as a solvent proved to be the most favorable for use in the preparation of highly enriched13C. The overall separations obtained as a function of the concentration of DNBA using 2.5 cm i.d. × 100 cm column ranged from 2.05 at 1Mto 1.69 at 2.84MFor 2MDNBA the maximum separation was 1.94. At this concentration of DNBA the overall separation as a function of flow rate ranged from 1.94 at 0.845 ml/cm2-min to 1.31 at 2.9 ml/cm2-min. Neither the rate of exchange nor the overall separations were improved by use of catalysts. Increasing the diameter twofold resulted in little or no loss in overall separations. On the basis of the properties of the system and the data obtained with respect to the above variables, design calculations were made for a six-stage tapered cascade. These calculations were based on a flow of 40 ml/min of 2MDNBA in TEA, giving a maximum transport of 7.1 × 10−3mmole/min or a maximum production rate of 130 mg13C/day. The cascade was operated for about 5 months during which period gram quantities of 67%13C were produced.

ISSN:0037-2366    

DOI:10.1080/00372367508058040

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Throughout each programmed multiple development (PMD) in thin-layer chromatography (TLC), the thin-layer plate remains in contact with the solvent. An important result is a spot reconcentration that narrows spots of low as well as highRFSpot reconcentration occurs as an interaction between the spot molecules and the solvent front, during both solvent advance and solvent removal. When solvent is removed by heating in PMD, two separate mechanisms for spot reconcentration exist: (a) solvent removal by heating, and (b) solvent advance that follows solvent removal by heating. These mechanisms have been experimentally isolated and studied quantitatively. A chromatographic quality indexQMD= RRWwas used for expression of the results. HereRis resolution—the center-to-center separation of the spots divided by the average width of the spots—andRwis the maximum ratio of the spot top-to-bottom widths in the chromatogram. To make the measurements of the developed spots more precise and clear, all spots were formed into rings before development. The measurements show that if solvent is removed conventionally—by air-drying the plate away from the solvent reservoir between developments—it matters little whether the successive solvent advances are uniform (QMD= 2.1) or successively more extended (QMD= 1.5). Both compare with straight PMD, for whichQMD= 10.0. The chromatographic quality resulting from isolated solvent advances that follow solvent removal by heating is best for gentler, more prolonged heating (QMD= 3.0), but better for strong, brief heating (QMD= 2.3) than for no heating at all (Qmd= 1.5). The chromatographic quality resulting from solvent removal is better than that resulting from solvent advance whether the heating is as is preferable gentler and more prolonged (Qmdremoval = 4.3, Qmdadvance = 3.0), or strong and brief Qmd= 3.4), Qmd= 2.3). The full chromatographic quality of straight PMD (Qmd= 10.0) is obtained because the solvent advance and solvent removal mechanisms complement each other and are supplemented by prehead and initial, brief continuous development at the origin.

ISSN:0037-2366    

DOI:10.1080/00372367508058041

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Changes in peak shape which accompany the imposition of an electric field were examined by moments analysis. Although peak maxima shifted significantly, only slight changes were observed in the value of the peak mean. Column efficiencies calculated from the second central moment indicated that the field lowered the resistance to mass transfer, probably as a result of electric field-induced convection of the stationary phase.

ISSN:0037-2366    

DOI:10.1080/00372367508058042

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

A number of phenolic components of urine reactive to phosphomolybic acid were separated by the use of liquid thermal diffusion.

ISSN:0037-2366    

DOI:10.1080/00372367508058043

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The anion exchange behavior of a negatively charged complex of thorium is studied on Dowex-21 K. Various eluants were tried. Hydrochloric, sulfuric, and nitric acid, as well as chlorides, nitrates, and acetates of sodium and ammonium, were tested as eluants. The efficiency of various eluants was determined. Novel methods were developed for the separation of thorium from a large number of elements by the processes of selective sorption, selective elution, and gradient elution. The method was found to be applicable for the separation of thorium from fission product elements.

ISSN:0037-2366    

DOI:10.1080/00372367508058044

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The adsorption of uranium from a dilute aqueous solution by a large number of inorganic adsorbents has been investigated. A mixture of aluminum hydroxide, ferric hydroxide, and activated carbon in the weight ratio 1:3:4 has shown a high adsorbability for uranium. The separation of uranium from a dilute aqueous solution by this mixed adsorbent under various temperatures and pH values has been studied. The adsorbability was found to exhibit a maximum at pH 4.0 to 5.5 and to decrease with increasing temperature. A number of eluting solutions for the desorption of uranium from the mixed adsorbent were also tested; 1N(NH4)2CO3was found to be the most suitable eluting solution (93% recovery of uranium).

ISSN:0037-2366    

DOI:10.1080/00372367508058045

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Thorium phosphate papers have been prepared by treatment with thorium nitrate and phosphoric acid solutions. Several metal ions have been chromatographed on thorium phosphate paper. The effect of pH onRFvalues has been investigated. Some useful analytical separations of metal ions have been achieved by using only dilute mineral acid and a mixed solvent system.

ISSN:0037-2366    

DOI:10.1080/00372367508058046

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0037-2366    

DOI:10.1080/00372367508058038

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor