Evaluation of Porous Silica Beads as Packing Material for Chromatographic Columns Application in Gas-Solid Chromatography C. L. Guillemin, Madeleine LePage, R. Beau, and A. J, de Vries Produits Chimiques PPchiney-Saint-Gobain, Centre deRecherches, 92, Anton y , France A new support-porous silica beads with controlled texture-allows effective separations in gas-solid chromatography not only of permanent gases but also of complex mixtures of various chemical compounds. The effect of the characteristic parameters of the packing material, in particular pore size distribution and specific surface area, has been studied on the basis of separation efficiency in isothermal or programmed temperature o eration. Good separations have been achieved for Eght hydrocarbons: normal and isobutanes, normal and isobutenes, aromatics, high boiling normal hydrocarbons, halogenated hydrocarbons, and alcohols. In some cases it is advantageous to add slight amounts of a modifier (Carbowax 20 M) to suppress peaktailing.
ical nature of the surface, allow the separation not only of permanent gases but also of nonvolatile compounds. Recently a new packing material has been developed which has been employed in gel permeation chromatography. This is in the form of material, described by de Vries et al. perfectly spherical beads of porous silica. These beads are available in different particle sizes, and the pore size distribution can be chosen in a wide range, depending on the application considered. This packing material can also be employed for the separation of molecules of various chemical nature by means of gas-solid chromatography.
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EXPERZMENTAL
DURING THE PAST FEW YEARS, a number of investigations have been published on the modifications of solid adsorbents used in gas-solid chromatography in order to perform separations comparable to those currently obtained in gas-liquid chromatography. Some authors, in particular Kiselev (1-3) and Scott (4, 5), have shown that appropriate treatments, resulting in a modification of the internal texture or the chem(1) A. V. Kiselev, “Gas Chromatography, 1962,” M. Van Swaay, ed., p. 34, Butterworths, London, 1963. (2) Y. I. Yaschin, S. P. Zhdanov, and A. V. Kiselev, “Gas Chromatography, 1963,” H. P. Angele and G. H. Struppe, eds., p. 402, Akademie Verlag, Berlin, 1963. (3) A. V. Kiselev, “Gas Chromatography, 1964,” A. Golup, ed., p. 238, Institute of Petroleum, London, 1965.
Gas chromatography experiments were performed with a Carlo Erba, Model C apparatus, equipped with a flame ionization detector and operated under either isothermal or linear programmed temperature conditions. Columns of 4-mm internal diameter and 1 to 3 meters in length were chosen. After filling the column, the silica beads of particle size
(4) C. G. Scott, “Gas Chromatography, 1962,” M. Van Swaay, ed., p. 36, Butterworths, London, 1963. ( 5 ) C. G. Scott and C. G. S. Phillips, “Gas Chromatography, 1964,” A. Goldup, ed., p. 266, Institute of Petroleum, London, 1965. (6) A. J. de Vries, M. LePage, R. Beau, and C. L. Guillemin, ANAL. CHEM.,39,935 (1967).
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Figure 1. Pore size distribution of five samples of silica beads 0.30
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ANALYTICAL CHEMISTRY
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Figure 2. Separation of 50 % mixture by weight of pentane-hexane on silica beads 60 to 80 mesh (175 tjs 250 microns) were heated in situ at 200" C for one hour. The carrier gas was nitrogen, and the flow rate was 1.8 liters per hour. Gaseous or liquid iamples were injected by means of a Hamilton syringe. Figure 1 shows the pore size distribution of five samples of silica beads used in our investigations. Pore size distribution was determined by means of a Carlo Erba mercury intrusion porosimeter.
RESULTS AND DISCUSSION
Column Efficiency. Figure 2 and Table I show the separation of a 50% mixture by weight of pentane and hexane, obtained with six samples of silica beads of different specific surface areas. Tests have been made under the following conditions: column length 1 meter at 60" C, sample injection 1 pl. The other conditions were the same as above. The number of theoretical plates per meter, N , and the peak resolution have been determined for the hexane peak by applying the well-known formulas:
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Figure 3. Separation of ethylene, n-butane, and isobutane
Figure 4. Separation of butenes
1-meter column. Silica ,beads, 480 sq meters per gram. Temperature 50" C
3-meter columns. Silica beads, 25 sq meters per gram. Temperature 50" C VOL. 39,
NO. 8, JULY 1967
941
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3-meter column. Silica beads, 0.9 sq meter per gram. Initial temperature 100 C. Programmed temperature 25 O C per minute
Table I.
Column Efficiency for Pentane-Hexane Separation
Support characteristics Type of Specific silica surface Pore beads area, sq m/g radius, A A 480
