Gas-solid chromatography with salt-modified porous silica beads

Abstract

The differential enthalpies, entropies, and free energies of adsorption for the functional groups of substituted hydrocarbons on salt-modified porous silica beads have been determined using elution gas chromatography. The effect of adsorbent surface area and of surface modification on these thermodynamic parameters has been studied to establish optimum conditions for selective separations. Various coating salts are compared and data are presented for the functional group contributions to adsorption on Porasil C modified with Na2S04, NaCI, LiBr, Na3P04, Na2Mo04, NiS04, C0SO4, AI2(S04)3, and Cr2(S04)3. Surface treatment of the porous silica with hexamethyldisilazane eliminates the specific interactions due to olefinic and aromatic pi electron systems. This provides a basis for evaluation of substituent contributions to aromatic pi electron density. Examples of optimized separations of difficult mixtures are presented.Use of salt-modified activated aluminas in gas-solid chromatography, which was discussed initially by Scott (/), has been the subject of several detailed studies (2, 3). Recent investigations (4-7) have established that the interaction between a sórbate molecule and a salt-modified alumina is a combination of nonspecific and specific contributions. This previous work has shown that the overall adsorbentadsorbate interaction is dependent upon the nature of the modifying salt and the adsorbent. As a part of this earlier work, salt-modified porous silica beads have been compared with modified aluminas. The porous silica beads have desirable properties for gas-solid chromatography and provide selective interactions that are different from those for aluminas.

Gas-solid chromatographic properties of alkali-metal modified silica

“…Thus, contributions due to the three bonds of the benzene ring could be evaluated by measuring the vertical distance between the point for n-hexane on the normal alkane line and the point for benzene. Similar measurements have been made with regard to functional group contributions to the thermodynamic properties of a wide variety of solutes with saltcoated adsorbents by Sawyer and co-workers (7)(8)(9)(10)(11)(12); however, this approach was not warranted in this initial work because of the small number of solutes employed. We hope soon to report data for a much larger number of adsorbates for which such correlations will be attempted.…”

Electrochemistry of molybdenum(VI,V)-8-quinolinol complexes in dimethyl sulfoxide

“…The gas chromatographic analysis for ethylene was performed on a 10% Na3PC>4-Porasil C column at 60°using a Varían Aerograph Series 1200 gas chromatograph. 19 The system was calibrated with CP grade ethylene (Matheson Co.).…”

Nature of nonspecific interactions in gas-solid chromatography

“…The apparent retention volume, VR', was then calculated from the relation Vs' = tB'-(TcITA)-f-Fa (9) where Tc and TA are the column and flowmeter temperatures (°K), respectively, Fa is the volume flow-rate at ambient temperature and pressure, and/is the James-Martin gas compressibility correction factor. The apparent retention volumes were converted to corrected retention volumes, VR, by VR = VR' -Va (10) (16) W. L. Jolly, "Synthetic Inorganic Chemistry," Prentice-Hall, Englewood Cliffs, N.J., 1960, pp 182-3. where V¿ is the system dead volume (void space) as determined by injection of neon at the column temperature.…”