L. B. Rogers

Improved Chromatographic Resolution from Pressure-Induced Changes in Liquid—Solid Distribution Ratios

Abstract A high-pressure liquid chromatograph is described which will deliver eluent under pressures up to 60000 lb/in.2 This instrument is compared to other common liquid chromatographic methods using Methyl and Ethyl Orange on silica. High pressures had a marked effect upon each distribution ratio and improved the separation.

Investigation of Pressure-Induced Changes in the Chromatographic Selectivity of Methyl and Ethyl Orange on Silica Gel

Abstract With water as the solvent and two azo dyes as the exemplary solutes, the modification of selectivity through pressure-induced changes in column equilibria has been shown to be significant using a chromatograph capable of going to 4000 kg/cm2. Data from high-pressure conductance, spectroscopy, adsorption chromatography, and steric-exclusion chromatography indicated that the primary contribution to the pressure shifts in selectivity was occurring in the bulk solution. An explanation correlating the various experimental observations is offered.

Gel Chromatographic Behavior of Aqueous Ferric Nitrate

Abstract Ferric nitrate solutions with different degrees of hydrolysis were investigated on polydextran gels having various exclusion limits. Typically chromatograms exhibited two well-resolved peaks, one at the void volume and the other at the total liquid volume of the gel. The respective peaks corresponded to higher and lower molecular weight fractions of the iron in the injected sample. Similar behavior was observed in “negative-peak” investigations where the positions of sample and eluent were reversed. Frontal analysis of the iron solution showed two breakthroughs corresponding to excluded iron moving in the void volume and admitted iron moving near the total liquid volume of the gel. The molecular size distribution of the ferric nitrate samples was studied as a function of OH-Fe ratio by noting changes in the percentage of iron in the respective fractions for gels having known exclusion limits.

Nuclear Magnetic Resonance Measurements of Line Width, Chemical Shift, and Intensity for Molecules Adsorbed on Silica

Abstract High-resolution NMR spectra were taken of molecules adsorbed on silica to determine the effects of specific surface interactions on line widths, chemical shifts, equilibria, and freezing points. Line widths were measured for cyclohexane, benzene, acetone, and methanol adsorbed at monolayer coverage. Hydrogen bonding to the surface was evident for the latter two compounds from the decrease in line width when the silica was silanized. In addition, the hydroxyl hydrogen of methanol was found to undergo exchange with the surface. After silanization, chemical-shift changes were noted for cyclohexane, p-xylene, mesitylene, acetone, and methyl acetate. Attempts were made to explain the magnitude of the changes by comparison with data from infrared spectroscopy and gas-solid chromatography. Chemical shifts of mixtures of adsorbates were studied to gain additional information on relative adsorption strengths. The tautomeric equilibrium of adsorbed acetylacetone was measured from the relative integrated in...

Effects of Slow Mass Transfer When Using Microporous Adsorbents in Gas-- Solid Chromatography.

Abstract The elution behaviors of CH4, C2H6, n-C3H8, iso-C4H10, Ar. O2, N2, and SF6 were studied in A-type zeolites containing K+, Na+, Li+, Sr2+, Ca2+, and Mg2+ and on a 10X zeolite. Temperature- and flow-dependent tailing of peaks and changes in retention volume with flow rate were found for those adsorbates able only to partially penetrate the pores. When diffusivities were large enough to allow total access to the pores, molecular size and the degree of adsorption for the adsorbate had significant effects — on HETP values.

Effect of an Electric Field on Gas Chromatographic Retentions by Liquid Crystals

Abstract Reversible changes in gas-chromatographic peak shape and retention time were produced by applying an electric field across a capillary column that employed a liquid crystal as a stationary phase. In general, applied potential caused peaks to be retained longer and to be more nearly symmetrical in shape. The behavior of a variety of substances has been studied over a range of temperatures.

Effect of Loading on Separation Efficiency Using Steric Exclusion Chromatography

Abstract Resolution and resolution-per-unit-time have been studied for columns from 4 to 21 mm i.d. The effects of sample size, particle diameter, and linear flow rate were determined. Greatest resolution was obtained for the largest diameter column, and it was attributed to a loading effect. In a related study, efficiency was examined as a function of column diameter for a constant amount of gel and a constant retention time. The narrower columns gave more plates, but their HETP values were also greater.

Effects of Adsorbent Properties on Nuclear Magnetic Resonance Line Widths of Adsorbates

Abstract An analytical NMR spectrometer has been used to measure line widths of molecules adsorbed on silica so as to investigate the capabilities and limitations of such measurements. Comparisons of line widths with transverse relaxation times (T 2) for the same samples showed that the observed resonance lines were inhomogeneously broadened. Consequently, line widths are not a reliable way of obtaining T 2 values or activation energies. The porosity of silica appeared to be an important factor governing adsorbate line widths, the narrowest lines being observed with adsorbents having the largest pore diameters. The narrow resonance lines observed for molecules adsorbed at low coverages on pyrogenic silica have been attributed to the nonporous surface, small particle size, and high purity of that adsorbent. Broadening of lines at high surface coverages on pyrogenic silica appeared to be due to slow exchange of molecules between surface and bulk states having different chemical shifts. Potential application...

Enrichment and Fractionation by Foaming

Abstract In a binary mixture of surface-active sodium salts of dodecylsulfate, benzenesulfonate and dodecylbenzenesulfonate, each substance appeared to act independently over the range of concentrations examined. There was no evidence of competition like that reported earlier for a system that involved ion-pairing. In cases such as those in the present study, degradation of the separation may result when the less surface-active species is initially much lower in concentration. Measurements of the volume of solution in the flask during a foaming experiment confirmed the expectation that faster gas flows and higher concentrations of surface-active species lead to higher holdup and longer time to reach a steady state.

Gas-Chromatographic Behavior of Pretreated Silica Gels

Abstract Silica gels were prepared by acid precipitation and dehydrated by refluxing in the presence of various aromatic solvents. The pretreatment was found to change the surface area and packing density of the gels. The chromatographic behavior of these gels toward organic adsorbates showed the treated gels to give better separations and resolution under time-normalized conditions. The columns were found to be thermally stable up to 200°C for long periods of time.