Method for Winding Long Capillary Columns J. G. Valenta and Eldon A. Trame Rockhurst College, 5225 Troost Avenue, Kansas City, Mo. 64 110
There is a need for a simple, easily applied method for winding long capillary columns to produce a uniform, compact coil rigidly held in a low-mass support with open spacing between the coils of tubing. Spacing is necessary t o allow rapid air flow around the tubing to facilitate heat transfer during temperature programming ( I , 2). We have found it difficult to apply the method of McEwen ( 3 ) , which spaces the coils of tubing on a mandrel bearing narrow strips of steel sheet perforated with %&-inchholes and cut along the centers of adjacent rows of holes. The strips of steel must stand on edge to function as spacers, but they capsize easily as the tubing is wound around them. The method of Warden and Schoenig ( 2 ) avoids some of the problems of McEwen's method, but a t the cost of silver brazing the steel strips to supports on the mandrel to hold them upright, and the brazing must be done during the winding process. We report a simple procedure for easily obtaining the desiderata expressed above with stainless steel capillary tubing t o lengths far exceeding 1000 feet. As in the methods cited, the technique of spacing the successive loops of tubing is the crucial feature. The spacers used are fabricated from a stainless steel sieve material, Ty-Rod screen (W. S. Tyler, Inc., 8200 Tyler Blvd., Mentor, Ohio 44060), Figure 1. Ty-Rod No. 9425, having 0.062-inch openings between 0.063-inch wire and 2inch long slots has been used in this laboratory to wind columns of 0.0625-inch 0.d. tubing. Ty-Rod No. 9900 screen, having 0.032-inch openings between 0.035-inch wire and 1inch long slots would appear suitable for winding columns of 0.0312-inch 0.d. tubing. This screen is cut and bent a t the places indicated (Figure 1)to produce the spacers. The manufacturer will cut and bend the screen. A sketch showing pertinent dimensions is required for this service. If spacer fabrication is to be done locally, the piece of screen ordered must have the direction of the slots specified to avoid appreciable wastage: if the length of the slot is to be parallel to the long dimension of the piece ordered, it is specified as "Slots L"; if parallel to the short dimension, "Slots S." The length of the spacers is determined by the desired height of the final column. The depth of the slots must accommodate the number of coiled layers in the finished column. Excess tine length protruding beyond the outermost coiled layer can easily be reduced by tapping on the ends of the tines to drive the spacers back into the hollow central core of the columns. The mandrel on which the spacers are placed for the winding operation is made of wooden disks aligned on a length of Ya-inch all-thread rod. Three %-inch wood disks are cut with a diameter equal to the blower intake a t the bottom of the oven, and 3/a-inch holes bored in their centers. These disks are placed on the rod as shown (Figure 2) and the spacers are held, about 1%inches apart, around the periphery of the disks by rubber bands (Figure 2). Winding should begin with, of course, enough excess tubing left unwound so as to reach the injector or detector fitting. The tubing is then guided into the first slot a t the end (1) L. S. Ettre, "Open Tubular Columns in Gas Chromatography," Plenum Press, New York, N.Y., 1965, pp 120-121. (2) T.Warden and D. Schoenig, J. Chromatogr. Sci., 10, 727 (1972). (3) D.J. McEwen, Anal. Chem., 35, 1636 (1963).
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RIGHT ANGLE BEND
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ORIGINAL SCREEN
SPACER
Figure 1. Fabrication of capillary tubing spacer from Ty-Rod screen
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Figure 2. Use of spacer on mandrel (1) Spacer: only one spacer is shown in place, (2) wooden disk, (3) rubber band, (4) 3/8-inchall-thread rod, (5, 6) handles at right angles to each other; 12 X 1y4 X '/&inch wood, (7) nut
of the spacers and the mandrel rotated. The spacers are held very securely in place on the mandrel after a few turns. The rubber bands that originally held them to the mandrel are easily removed through the open central core of the completed column after the mandrel is removed. To separate one coiled layer from the next, lengths of l&-inch aluminum or stainless steel wire are laid parallel to each other a t right angles to the column tubing on the layer just completed. A sufficient number of these wires, 3 or 4 between each spacer, are used to prevent tubing in the layer being wound from touching the layer just completed. These wires are held in place against the layer beneath them by a rubber band stretched completely around the circumference of the column. The wires are arranged under the rubber band, a few turns of the next layer are wound over the wires, the rubber band is removed, and the layer completed. Winding need not be done on a lathe. The ends of the all-thread rod can be slipped into the hollow extension arms of ordinary laboratory extension clamps, which are held with the usual clamp-holders to large ring stands, clamped securely to a work table. The mandrel is then
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Figure 3. TWO '&nch o d. X 500-tt long capillary columns wound on spacers made from No. 9425 Ty-Rod screen
pulled around with the light wooden handles (Figure 2) screwed onto the outside disks. T o facilitate tight winding, it is well to create a drag on the tubing. One way of doing this is to weave the tubing between three horizontally clamped in a plane a few fe bur inches above it. If dual columns are aesirea, rwo ierig~iixut ruuing well in excess of 500 feet each can he wound simultaneously on the mandrel. In this case, an even number of spacer slots must be employed; otherwise the last odd turn will not he properly supported by the aluminum wires bearing against the layer beneath, and the winding a t the end of the column will not he uniform.
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After the column is wound, the outer nuts (Figure 2) are removed and the disks are easily withdrawn by tapping the ends of the all-thread rod with a mallet. Note that the inner disk must not he held in place by nuts, but simply slipped over the rod to support the spacers a t midpoint; it too is removed from the central opening of the finished column without difficulty. Using the procedure described, we have wound two single 500-foot columns and two dual 500-foot (total 1000 feet of tube) columns (Figure 3). We have also wound one 500foot column by this method for use in the tall, narrow oven of a biomedical gas chromatograph. For this application, the column is put into the oven with the open central core oriented horizontally. The length of the spacers is so chosen that the height X diameter of the finished column forms a rectangular cross section that just fits the depth X width of the oven. The column thus completely fills the cross section of the oven, providing a uniform path for the air from the blower over the coils of column tubing. Since this method of winding produces a column which is about 50% open space, there is no significant obstruction to air circulation in the oven in this particular application.
ACKNOWLEDGMENT We thank hAarilyn K. Rigby for assistance. .Received for review January 28, 1974. Accepted May 17 ,. ..> researcn sup1974. This W O ~ Kwas aone in conneczion wim ported by the US. Army Research Office-Durham, and bj the Rockhurst College Faculty Research Fund.
* ANALYTICAL CHEMISTRY, VOL. 46. NO, 9. AUGUST 1974
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