vated Linde Molecular Sieve 4A. The NMR spectrum of benzyl alcohol in this solvent is shown in Figure 1C and is in agreement with the results reported by Chapman and King (1). The hydroxyl and methylene groups are again split; however, no evidence of the prescan be seen. ence of Ph-CH2-OD The HDO peak has almost vanished. The relative integrals in each of the three systems are compared in Table I.
After essentially complete removal of labile deuterium from the DMSO-dc, further traces of HzO absorbed in the solvent from the atmosphere or introduced with the solute will not adversely affect the integrals of exchangeable protons in the system. This technique has been used routinely to monitor all DMSO-& received in this laboratory. A S a result we have been able to obtain accurate
NMR integrals of labile protons, and provide valuable information for organic structural determinations. LITERATURE CITED
(1) Chapman, 0. L., King, R. W., J . Am. Chem. SOC.86, 1256 (1964). (2) Giessner-httre, Ann. PhW. 9, 557 (1964); C.A 62, 7269d (1965). (3) TraJrnham, J , &,, Knesel, G. A., J. Am. Chem. SOC.87, 4220 (1965).
c.,
ew Technique for Coating and Packing of Glass Bead Columns for Gas Chromatography 0.E. Wilkinsonl and J. H. Gibson, Department of Chemistry, Colorado State University, Fort Collins, Colo. HE PACKING of glass bead columns T p r e s e n t s a difficult problem, especially when the quantity of the stationary liquid phase exceeds approximately 0.10 to 0.25% by weight (2,3). Beads coated with materials that are “tacky” at room temperature-e.g., Apiezon L, silicone grease, Se 30 gum rubber, etc.-tend to clump and are not capable of being packed into tubular columns by conventional packing techniques which require a free flowing material. In addition to the problem of packing beads coated with liquids or grease-like materials, it has been observed by the author and others (3) that in coating the beads themselves with any stationary phase a significant portion of the coating material is lost to the walls of the vessel in which the beads are contained during solvent evaporation. Using weighed portions of the coating materials is, therefore, not a true measure of the final coating concentration. To the authors’ knowledge, no attempt has been made to overcome the latter problem except to use an amount of coating material in excess of the amount desired and to determine the final coating concentration after the solvent has been evaporated and the beads dried. Several approaches have been proposed to overconie the problem of packing glass beads in tubular columns. “On column” procedures (1,4) have been used in which the solvent containing the desired stationary liquid phase
is passed through the column which contains the beads, which were previously packed in the dry uncoated form. In this method, some of the coating material adheres t o the beads, but control of amount deposited is not possible (3). Other suggestions have involved cooling the beads to a temperature sufficiently low t o solidify the coated phase. With silicone grease, or Apiezon L, this requires dry ice temperatures and necessitates keeping the column, as well as the beads, a t this temperature during the packing procedures. Even though the beads are free flowing under these temperature conditions, this technique has not proved practical because of the difficulty of refrigerating both the beads and the column simulbaneously. 9 less difficult and more practical technique involves using a ramrod and tapping the beads into the column small quantities a t a time ( 2 ) . This is possible in l/4-inch diameter tubing, but becomes difficult with smaller ‘/s-inch diameter tubes. Also, it is difficult to assure that no voids are formed which would result in poor column efficiency. Of particular interest in work in this laboratory was the coating of glass beads with such stationary liquid phases as Apiezone L, silicone grease, and Se 30, all of which cause the beads to adhere to one another when the coating phase is in excess of approximately 0.25%. TO facilitate the packing of beads coated with these materials into l/s-inch col-
umns, a procedure was developed which involved the flowing of the beads into the column as in conventional techniques for other supports. This is accomplished by filling the column with a water solution containing a small amount of nonionic surfacant which prevents the beads from adhering to one another. The coated beads, after being mixed and separated in a similar water surfactant solution, are then poured into the column with accompanying vibration. This procedure is analogous to the method normally used with the exception of the presence of the water-surfactant solution which acts to reduce the surface tension between the individual beads, and, therefore, prevents sticking. During the development of this packing technique several attempts were also made to eliminate the problem of the adherence of a substantial portion of the liquid phase material on the walls of the vessel used to contain the beads during the coating procedure. It was found that loss of the coating phase during this sbep could be essentially prevented by carrying out the solvent evaporation step in equipment made of Teflon (Du Pont). (See Tables I and 11) It will be noted that better than 90% of the calculated liquid phase concentration is actually found on the bead surface when using the Teflon beakers. Comparable results are listed for glass equipment in which the loss is approximately 2570 of the liquid phase. EXPERIMENTAL
Table 1.
Recovery of Liquid Phase (Apiezon L) on Glass Beads Using Teflon and Glass Coating Vessels
yo Liq. phase Coating vessel
Wt. beads used
Wt. liquid phase
Theo.
Found
Teflon beaker Glass R. B. flask
77.01 g. 76.54 g.
0.7701 g. 0.7654 g.
0.99 0.99
0.92 0.78
‘1972
e
ANALYTICAL CHEMISTRY
Preparation of the Coated Beads. I n the development of the technique for coating and packing of the glass beads, three stationary phases were studied: Apiezon L, Dow Corning silicone grease, and Se 30 gum rubber. These materials were deposited on the 1 Present address, hlcoa Research Labs. New Kensington, Pa.
,Id SWAGELOK "L" COLUMN
I/;
SWAGELOK
6 " TRANSPARENT TUBING
;/I
TO
'/e
SWAGELOK
Figure 1. Diagram of apparatus used in washing surfactant solution from packed columns
surface of the beads in concentrations ranging from o,5y0to 2% by weight. A weighed portion of the liquid phase was dissolved in a suitable solvent (in this case chloroform). The beads were then weighed into a Teflon beaker and covered with the solvent containing the coating phase. The Teflon beaker was then transferred to a shaker and heat was applied to completely remove the solvent. The shaker was used in this step rather than a rotary evaporator as only beakers of Teflon were available. After all visible solvent was removed in this step, the beads were further dried in a vacuuni oven. I n experiments designed to demonstrate the efficiency of coating that can be obtained when using Teflon beakers, the beads were stripped of the liquid phase and both the beads and amount of liquid were weighed to determine the per cent by weight of the coating material. Column Packing. The surfactant solution used to separate the coated beads was prepared by adding one drop of Dowfax nonionic surfactant No. 9N4 (Dow Chemical Co.) to approximately 100 ml. of water. This concentration results in a saturated solution of the surfactant which has a cloudy appearance. The dried coated beads are then transferred to this solution and thoroughly agitated with a glass rod, until the individual beads has-e separated from one another and no further clumping is observed. The column is prepared for packing by selecting the proper length tubing inch stainless steel used throughout) and bending into a U configuration. A funnel is attached to both ends of the column by means of plastic tubing. Surfactant solution, prepared as previously described, is then poured into the column until all air is removed and both funnels are approximately 1/4 full. The beads are then transferred from the surfactant solution used in the separation step to the funnels. While small amounts of the beads are alternately added to each of the funnels, vibration is provided t o the bottom of the column by means of a vibrator. (If, during this
step, clogging takes place a t the mouth of the tube, a small wire can be used to break up the obstruction.) This process is continued until both ends of the column are filled. At this point, the funnels are removed and both ends of the column plugged with glass wool. It is helpful a t this point to crimp slightly one of the column ends to prevent the glass wool plug from being dislodged during the removal of the surfactant solution which is retained in the column, To remove the surfactant solution after the column is packed, an aspirator or vacuum pump with satisfactory trap is placed in the crimped end of the column. The other end of the column is attached to a supply of compressed gas (helium), and approximately 50 lbs. of gas pressure is applied to the column, If the evacuating system is attached by means of a clear plastic tube, it can visibly be determined when the liquid solution has been purged by appearance of bubbles and foaming. At this point, approximately 10 ml. of a dioxane-water solution (1:1 mixture) is placed in a tube attached between the compressed gas supply and the column (See Figure 1). The pressure and vacuum are again applied and this material is rinsed through the column. This step is designed to remove any of the surfactant which might adhere to the beads and thus alter the characteristics of the packed column. The compressed gas is then allowed to flow through the column until no further evidence of liquid is observed a t the outlet. The column is then bent to the necessary configuration and fittings are attached if nut already provided. The column is then inserted in the gas chromatograph and preconditioned in the normal manner. DISCUSSION
By using this packing technique, it has been possible to pack glass bead columns with tacky liquid phases of concentrations up to 2y0. Larger per cent liquid phase coatings were not at-
Table II. Results Obtained with Various Liquid Phases When Using a Teflon Coating Vessel
Liquid phase
Theo., yo
Found, Yo
SE30 Polyethylene hpiezon L
1.0% 2.570 1.0%
0.97 2.28 0.93
tempted since microscopic examinations and column separating characteristics indicated that, even at 2Y0,excess liquid phase was present. To determine whether or not this method was capable of preparing a column which was evenly packed and contained no voids, the procedure was used in the packing of glass tubing columns of approximately the same internal diameter as i/s-inch stainless steel tubing. In no case were voids observed. In the lower concentration range (0.10% to 0.25%) columns packed by this technique were prepared and compared with columns of the same liquid phase loading packed by conventional methods. No differences in separating characteristics were noted between columns packed by the two procedures. It was also experimentally determined that the nonionic surfactant solution had no solvent effect on the liquid phase when used with the -4piezon L, silicon grease, Se 30, or Silicone fluid 710R. Its solubility effect on other possible liquid phases was not determined. It is felt, however, because the surfactant is nonionic in character, that liquid phases which have no significant solubility in water can be handled by this method. It is proposed, therefore, that columns can be very satisfactorily packed by this method when conventional techniques are not applicable, due to the self-adherence of glass beads. Also, the coating of glass beads with liquid phases of any desired concentration can be greatly facilitated by the use of Teflon equipment as determination of the liquid concentration is often not necessary after the solvent evaporation step. LITERATURE CITED
(1) Averill, W.,J . Gas Chromatog. 1 No. 1, 34 (1963). (2) Frederick, D. H., hIiranda, B. T., Cooke, D., ANAL. CHEM. 34, 1521 (1962). (3) Hawkes, S. J., Russell, C. P., Giddings, J. C., Ibid., 37, 1523 (1965). (4) Lysiyj, I., Newton, P. R., Ibul., 36, 949 (1964).
w.
WORKreported taken in part from M.S. Thesis of 0. E. Wilkinson, Colorado State University, 1965. Work supported by funds from Faculty Research Grant KO.237, Colorado State University and Kational Science Foundation under Grant NSF G-P5095.
VOL. 38, NO. 13, DECEMBER 1966
1973
